NACOR Bridging Course Series
Dispensing Contact Lenses - 1
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CONTACT LENS DISPENSING 1
Objectives
Upon completion of this course the student will be able to:
1. Demonstrate knowledge of the importance of obtaining a relevant medical and optical health history from the patient in order to complete an initial contact lens fitting and to provide organized ongoing care of the patient. 2. Develop a detailed patient file. 3. Understand the importance of taking measurements and performing assessment relative to the patient’s ocular status and suitability for contact lens wear. 4. Demonstrate knowledge of the use of ophthalmic instruments and devices to perform ocular measurements for contact lens fitting. 5. Identify anomalies in prescriptions that are indicators for contact lens fitting decisions. 6. Interpret readings, consider assessment data and apply knowledge to inform and support decisions. 7. Demonstrate an understanding of the affect of prescription and non- prescription drugs on contact lens wear.
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The Patient History Record
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Patient History Record A carefully kept patient record is the basis for successful contact lens fitting and aftercare. The record provides pertinent medical history plus a baseline of what measurements and observations represent ‘normal’ for the patient. The baseline measurements and observations allow the contact lens fitter to assess the impact of the contact lens on the cornea at all future patient appointments and to troubleshoot any contact lens related symptoms that emerge.
The Patient Record takes the contact lens fitter from: • initial intake of personal information of a new patient to • the initial assessment, • keratometer readings, • slit lamp evaluation, • trial lens fittings and • through to the contact lens follow-up.
Follow-up measurements and observations are recorded and added to the patient file. An organized protocol such as this is essential to providing the contact lens fitter with ability to best address the patient’s visual needs.
The Medical History
Why do we develop a detailed medical history including diseases and conditions of immediate relatives? Families have many factors in common, including their genes, environment, and lifestyle. Together, these factors can give clues to medical conditions that may run in a family. The specifics of medical history collected through the patient record determine the suitability for contact lens wear (for the new patient) and for continued contact lens wear (for the returning patient).
When the accumulated intake medical history data is considered in conjunction with the observations and measurements the contact lens fitter takes such as keratometer readings, slit lamp observations, visual acuity notations, tear flow and tear break-up time assessments the contact lens fitter can make best practice clinical decisions.
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Some contraindications for contact lens wear may be discovered in studying the medical history. For example: • Active eye disease or injury or any abnormal state of the cornea, conjunctiva or eyelids. • Use of any medications that are contraindicated with contact lenses or contact lens caring products including any and all eye medications. o Certain medications such as antihistamines, decongestants, diuretics, muscle relaxants, tranquilizers, and those in motion sickness may cause eye dryness, increased contact lens awareness or blurred vision.
The Patient Record Includes
In addition to the patient’s medical history, and in order to establish a baseline of what is considered ‘normal’ for the patient the contact lens fitter will note in the patient record: • Current prescription • Visual Acuity o Monocular for both distance and reading without and with eyeglasses/contact lenses • Tear Volume /Tear Break-up Time (TBUT) • Horizontal Visible Iris Diameter (HVID) measurement • Vertical Palpebral Aperture measurement (VPA) • Pupil diameter measurement – performed in both light and dim conditions • ‘K’ Readings • Slit Lamp readings and observations – for example, any pre-fitting anomalies present on the cornea and sclera. • Lid Position/Lid Tension – particularly important in fitting RGP lenses. The lids play an important role in positioning the contact lens especially in a translating design multifocal lens. • Lid Eversion notations – examine the superior tarsal plate for signs that may indicate signs of allergy or, if the patient is a current contact lens wearer evidence of mechanical irritation from the contact lens.
The fitting record will include: • Trial Lens specifications • Final Lens specifications 5 | P a g e
Contact Lens Follow-up Manifest Over-refraction (MOR) calculations
Samples of both a comprehensive medical history record and a patient contact lens fitting record appear in the resource tab in the Interactive version of this course.
Subjective and Objective Assessment At each patient visit the contact lens fitter must record subjective and objective assessments and symptoms. Subjective assessments and symptoms are those reported by the patient. For example, “My eyes seem very dry.” Objective assessments and symptoms are those observed by the contact lens fitter. For example, on slit lamp inspection the contact lens fitter may notice that the tear break-up time has been severely reduced since the patient’s last visit.
What is Considered ‘Normal’? It is beyond the scope of practice of Opticians to diagnose conditions. However, the initial intake assessment establishes baseline measurements and observations prior to performing a contact lens fit and this becomes a record of what is ‘normal’ for that patient. Any changes in those initial measurements and observations are considered ‘other than normal’.
Some symptoms a patient may experience upon being fit with contact lenses are considered ‘normal’. It is normal for the patient to have blurry vision upon initial insertion of the trial lenses. It is normal for the new patient to feel uncomfortable after a few hours of contact lens wear when he/she is building up his/her wearing time.
Contact lens fitters must educate patients about ‘normal’ adaptive symptoms and ‘normal’ wearing expectations so that the patient will know when to report symptoms that are ‘other than normal’. For example, you would say to the patient, “It is ‘other than normal’ to experience intense sharp pain when wearing contact lenses. If you experience this symptom immediately remove your contact lenses and see a vision care professional.”
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Conducting a Comprehensive Assessment
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Assessing Visual Acuity Assessing visual acuity (VA) prior to fitting contact lenses is critical to success because you need a basis for comparison once the contact lenses have been fit.
VA must be performed both monocularly and binocularly plus with and without eyeglasses/contact lenses.
When performing a new fit and assuming that the prescription is new, you can expect that myopes will see the same with their contact lenses as with their eyeglasses or one line better on the Snellen chart (or its equivalent). The reason for this is that the vertex distance has been eliminated because the contact lens sits on the cornea which increases the retinal image size.
The opposite is true for the hyperope. You can expect that hyperopes will see equal to or one line less on the Snellen chart with the contact lenses. The reason for this is that with eyeglasses the retinal images are magnified. When we fit the hyperope we eliminate the vertex distance and reduce the retinal image size. This leaves the hyperope with the initial impression that contact lens vision will not be as good as eyeglass vision. However once adaptation has taken place the patient will accept the contact lens vision as being ‘normal’.
A visual acuity assessment is performed at every follow up visit to make sure the VA does not change over time. Unless the patient needs a new eye examination, reduced VA is a sign to the Optician that the contact lens fitting should be re-assessed.
Tear and Lid Assessment The contact lens fitter will never achieve optimum fit and the patient will never experience expected comfort and wear time if the tear layer and the lids aren’t functioning efficiently. However, the contact lens fitter might be able to balance inefficiencies by careful selection of fitting parameters, lens
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modalities and appropriate solutions recommendations. But it’s best practice to start the fitting process with knowledge of any tear/lid anomalies rather than waiting until problems arise.
The Tear Volume Observing the pre-corneal film is known as a quantitative test. The Optician must assess whether or not the patient has sufficient tears to support successful contact lens wear. One way of doing this is to assess that volume of tears in the tear meniscus – also referred to as the lacrimal lake. A normal tear meniscus (located along the lower lid) is .25 mm. This is observed using the slit lamp with the cobalt blue filter and fluorescein. This information is placed in the patient health record and monitored over at each contact lens follow-up visit.
Another method of assessing tear volume is by using the Schirmer Tear Test. The Optician everts the lower lids and tucks the top of a Schirmer test strip beneath each lid. This is a timed test and the tear volume is indicated by how much of the test strip has been wet by the tears within the prescribed time. The scale below is an indicator of how dry eye issues can be detected using this test.
Normal is ≥15 mm wetting of the paper after 5 minutes. Mild is 14-9 mm wetting of the paper after 5 minutes. Moderate is 8-4 mm wetting of the paper after 5 minutes. Severe is <4 mm wetting of the paper after 5 minutes
Follow the link below for detailed instructions on how to perform a Schirmer test as reported on the website of the National Centre for Biotechnological Information (NCBI). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3284761
Years of wearing contact lenses can induce C.L.I.D.E. – Contact Lens Induced Dry Eye. CLIDE will cause a change in the normal lacrimal lake. The Optician might resolve this condition by changing the contact lens material or the modality of wear. 9 | P a g e
Information gathered from the patient during the collection of data for the medical and fitting history can provide the first clues of potential dry eye problems. A questionnaire format may not trigger the needed responses from the patient so the contact lens fitter will need to prompt by asking focused questions.
Here are some examples of the types of questions that need to be asked. • Do you ever have sore, scratchy, dry, gritty or burning eyes? • How often do your eyes have these symptoms? • Have you ever had drops prescribed or other treatments for dry eye? • Are your eyes unusually sensitive to cigarette smoke, smog, air conditioning or central heating? • Are you known to sleep with your eyes partly open? • Are your eyes irritated as you wake from sleep? • Do your eyes easily become very red and irritated when swimming in chlorinated OR FRESH WATER? • Are your eyes dry and irritated the day after drinking alcohol?
Follow the link below to read a Contact Lens Spectrum article on “What You Can Learn from the Tear Meniscus”.
https://www.clspectrum.com/issues/2006/january-2006/reader-s-forum
Tear Breakup Time The tear break-up time (TBUT) test is a qualitative test. This information is used by the Optician to determine modality and material of contact lens wear.
The Optician instills fluorescein using the cobalt blue filter on the slit lamp biomicroscope. The patient is asked to blink a couple of times to uniformly spread the pre-corneal film over the corneal surface and then asked to stare. The Optician counts quietly in seconds until the fluorescein dissipates showing areas of darkness.
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TBUT SCALE 15-20 seconds is normal 10-15 marginal 5 -10 dry Below 5 very dry
Follow the link below to view a video demonstrating TBUT as observed using fluorescein.
https://www.youtube.com/watch?v=qYx1lDUB6YU
Pre-corneal Film Function The function of the pre-corneal tear film is:
• Lubricates the ocular surface including lids and globe • Provides a quality optical surface • Flushes debris • Limites anti-microbial and nutritional function
Factors That Affect the Pre-corneal Film and Contact Lens Wear
Health History and Medications
Some health conditions and the treatments patients are receiving for those treatments can have an impact on the stability and integrity of the pre- corneal film plus the success of contact lens wear and good visual acuity. This is why it is so important to do a thorough health history interview.
The following are health conditions that have an impact on successful contact lens wear.
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Diabetes
An estimated 285 million people worldwide are affected by diabetes. More than 3 million Canadians have diabetes and this number is expected to reach 3.7 million by 2020
The most serious eye condition associated with Diabetes is diabetic retinopathy. It occurs when the tiny blood vessels at the back of your eye become blocked and leak.
How Diabetes Affects Contact Lens Wear
There are structural and functional changes to the corneal epithelium, endothelium and nerves in the diabetic patient. One of the functions of the epithelium is to provide a protective barrier for the interior layers of the cornea. The epithelium becomes more fragile consequently providing less protection against micro-organisms. It has been found that corneal lesions appear in ½ of the patients with diabetes mellitus. i
The endothelium has no ability to self-repair and it is the ultimate barrier and protection for the interior structures of the eye. It has been found that:
“In patients with diabetes, endothelial dysfunction appears to be a consistent finding; indeed, there is general agreement that hyperglycemia and diabetes lead to an impairment of NO production and activity.ii
This is a clear indicator that diabetic patients could more easily develop ocular complications during contact lens wear.
Pathological Conditions Related to the Eyelids
Any pathological condition related to the eyelids is a contraindication for contact lens wear. Even if the patient has an adequate tear volume if the lids can’t perform their function of spreading the tears over the cornea/contact lens the patient will experience wearing and visual acuity problems.
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Blepharitis is an inflammation of the eyelids and is the most common cause of dry eyes. It can result from:
• An excess growth of bacteria that’s normally found on the skin
• A blocked oil gland on the eyelid
• A hormone imbalance
• Allergies
How Blepharitis Affects Contact Lens Wear
Blepharitis is also called Meibomian Gland Dysfunction (MGD). Because blepharitis causes the eyelids to be red, itchy and a little swollen the contact lenses aren’t going to be comfortable. The patient will have a tendency to rub his/her eyes thus dislodging the contact lenses or worse – causing damage to the epithelium. The lid margins may be crusty and the tears may be oily causing the contact lenses to become dirty which will in turn have a negative impact on the fit and comfort of the lenses.
Blepharitis is also associated with dry eye syndrome which is another contraindication to comfortable contact lens wear and best vision. If the patient has chronic blepharitis his/her ability to wear contact lenses will be severely limited. If the patient has periodic episodes of blepharitis he/she should seek treatment from a physician and discontinue wear until the condition has been cleared.
Hyperthyroidism
This condition results lagophthalmos (improper closure of the eyelids upon a blink) which affects centration of the lens. It also results in proptosis (bulging of the eye) which contributes to the inability of the lids to properly close and which also leads to dry eyes since the lids aren’t able to refresh the tear layer upon blink.
How Hyperthyroidism Affects Contact Lens Wear
Ocular Symptoms:
• Double vision
• Photophobia (light sensitivity) 13 | P a g e
• Reduced vision in severe cases
• Dry eyes
It is easy to see why contact lenses may not be the first and best choice for vision correction with the patient who suffers from hyperthyroidism.
Inflammatory Arthritis
Ocular Symptoms:
• Dry eyes
• Eye redness
• Eye inflammation
• Gritty feeling in the eyes
How Arthritis Affects Contact Lens Wear
Patients with dry eyes are always a challenge for the contact lens fitter. In addition to dry eyes the arthritic patient may experience:
A patient who suffers from arthritis needs to be educated about the limited expectations of comfort and wear before moving forward with a new fitting. Patients who are already contact lens wearers and who develop arthritis must also be educated and retrained regarding reporting the signs and symptoms listed above AND further must be seen more frequently than he/she has been prior to becoming arthritic.
Pregnancy and Contact Lens Wear
Changes in hormone levels, fluid retention, and blood volume, can all distort vision during pregnancy. Thus, contacts prescribed before pregnancy should be used throughout pregnancy; new prescriptions should only be obtained after giving birth.
Cold Sores and Herpes
Cold sores are usually caused by the herpes simplex virus (HSV) type 1.
Cold Sores Herpes and Contact Lens Wear
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There is a risk of infecting the eyes with the cold sore virus if contact lenses become contaminated. The best course of action is to wait until the patient has been cleared of the virus before dispensing contact lenses. If for some reason (such as work or lifestyle) the patient must wear contact lenses during their treatment for the virus, he/she should be strongly advised to wash their hands thoroughly before touching their contact lenses and if possible use daily disposables until the virus treatment has been completed.
Contact Lens Wear and Dry Eyes
Contact Lens Induced Dry Eye (CLIDE) symptoms are the leading cause of patients discontinuing contact lens wear. There are new technologies and approaches to fitting that can assist in these cases.
Contact Lenses Recommended for Patients with Dry Eye
Daily contact lenses are thrown away every day. They usually have higher water content and higher oxygen permeability. They are not worn long enough for the material to collect deposits making the lenses more comfortable for this category of patient.
Rigid Gas Permeable and Scleral lenses are oxygen permeable but they do not draw moisture from the tear system. Instead they depend on the tears to provide a cushion (a tear layer) on which the lens rides. Tears are important to the successful wearing of these lens materials but they do not make an existing dry eye problem worse as regular soft lenses do.
Silicone Hydrogel lenses have a number of features that may contribute to the reduction in sensations of dryness. They can therefore increase the wearing time. In addition to high oxygen transmissibility they also have improved wetting qualities, a medium to high water content, and have a low dehydration tendency.
Measuring the HVID and the VPA Using a P.D. ruler, a topographer, a slit lamp or a loupe the Optician measures the horizontal visible iris diameter (HVID). This gives the fitter an approximate idea of the diameter of the cornea. It has been found that on average the cornea is 1.5 mm larger than the iris 15 | P a g e
diameter but the approximation is a good starting point for selecting a trial lens.
The Optician then measures the distance between the upper and lower eyelid known as the Vertical Palpebral Aperture (VPA). If the VPA is smaller than average the fitter might choose a smaller diameter lens so that the patient won’t have a difficult time inserting and removing the lens. The VPA can range in measurement from 7.9 mm – 12.3 mm. The VPA is particularly significant when fitting rigid gas permeable lenses.
Follow the link below to read an article on how to measure HVID. https://specialeyesqc.com/how-to-measure-hvid.php
Pupil Size Measuring pupil size is particularly important when fitting multifocal contact lenses. Because the contact lens floats on the cornea upon blink the power zones of the lenses will be displaced. If the distance power zone is smaller than the size of the pupil the patient will experience intermittent blurriness of vision.
A second consideration is that pupils will dilate and constrict according to lighting conditions. Consequently, when considering the multifocal contact lens design the contact lens fitter must measure pupil size in both light and darkened conditions.
Follow the link below and read the paragraph on “The Role of the Pupil”.
http://www.reviewofcontactlenses.com/content/c/23463
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The Keratometer
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The Keratometer
An important key to the success in fitting contact lenses is accurately taking corneal curvature readings and using that information along with the patient’s prescription and vocational/avocational needs to determine the final lens material and design.
The keratometer is also referred to as an ophthalmometer. Three sets of keratometer (“K”) readings should be taken per eye. The mean (middle of the three) reading for each eye should be recorded on the patient history file. These will be used later along with the patient’s prescription to determine the type of contact lens.
The mean reading must be recorded to the nearest 0.13D. The horizontal and vertical reading must be within +/- 0.25D.
The following is a guideline of tolerances for measurements of corneal toricity:
Corneal Toricity Tolerance up to 0.88D +/- 015 from 1.00 to 2.50D +/- 010 2.63 or greater +/- 005
Classification of Type of Astigmatism
It is also important to determine the classification of astigmatism. • If the axis of the flattest “K” reading falls between 0-020 or 160–180 the patient has with the rule astigmatism WTR. For example: 42.25 @ 180 / 45.25 @ 090 42.00 @ 180 / 45.00 @ 090 42.00 @ 180 / 45.00 @ 090 THE MEAN 42.00 @180 / 45.00 @090
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• If the axis of the flattest “K’ reading falls between 070-090 or 090 – 110 the astigmatism is classified as against the rule ATR. For Example: 42.25 @ 180 / 45.25 @ 090 42.00 @ 180 / 45.00 @ 090 42.00 @ 180 / 45.00 @ 090 THE MEAN 42.00 @180 / 45.00 @090
• If the axis of the flattest “K” falls between 021 -069 or 111 – 159 the classification on the astigmatism is oblique
For example: 42.25 @ 045 / 44.00 @ 135 42.00 @ 045 / 44.00 @ 135 42.00 @ 045 / 44.00 @ 135 THE MEAN 42.00 @045 / 44.00 @ 135
A keratometer is also used to monitor the “k” readings at every follow–up visit to make sure there is no change in corneal curvature. If there is a change the Optician must determine the cause and make the necessary changes to the contact lens fitting.
Follow the link below and read an article called “The Importance of Keratometer Readings”. Embedded in this article is an instructional video on the structure and uses of the keratometer.
https://www.optometrytimes.com/editors-choice-opt/why-keratometry-important
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The Slit Lamp Biomicroscope
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Slit Lamp Biomicroscopy
The overall eye health must be assessed prior to fitting contact lenses. Careful observation of the pre-corneal film, ocular surface and other adnexa measurements are made and findings recorded in the patient history file. The contact lens fitter uses the slit lamp biomicroscope and employs various methods of illumination in order to view the eye from different angles and using different magnifications. There are three basic types of illumination: Diffuse, Direct and Indirect. These are used in combination with specific positions and widths of the illumination along with varying angles of separation between the ocular and the source of the illumination.
Diffuse illumination is typically the first method of illumination used to determine general ocular health. • Lighting is arranged so that the eye being viewed is illuminated from many different directions • Used for general observation of the eye prior and post contact lens fitting • Lamp house and oculars are set 045° apart • Magnification is low 10X • Open the slit completely horizontally and vertically
Direct Focal Illumination: • Used for viewing the front structures of the eye • Lamp house and oculars are set 045° apart • Magnification is increased to 16-25X • The slit beam and the microscope are both focused sharply on the structure being observed. It is used for observing: . The tear layer . Thinning and thickening of the corneal surface . The depth of foreign bodies . The crystalline lens . Estimate the depth of the anterior chamber
Other uses for Direct Focal Illumination • Observation of the pre-corneal film. 21 | P a g e
• Depth of a corneal scar. • Depth of an embedded foreign body. • Detect changes in corneal thickness. • Lids, eyelashes, caruncle are easily observed with this method of illumination • The entire extent of a corneal scar can be observed • Neovascularization • Infiltration • Edema
Direct Focal Illumination: Optic Section: This method of illumination can view the layers of the cornea. • This shows the layers of the cornea. • The bright outer layer is the tear layer. • The dark line right after the bright layer is epithelium • Bowmans layer bright line • The stroma as the main body • The dark line at the end is the endothelium
Follow the link below to see a demonstration of the slit lamp technique used to observe and optic section. https://www.jnjvisioncare.ae/slit-lamp-techniques/optical-section
Conical Beam Illumination A conical beam is a small round circle. This is achieved by adjusting the vertical to a minimum and adjusting the horizontal to a minimum. It is used for observing: • Aqueous flare and cells • To observe debris floating in the anterior chamber
Specular Reflection Illumination
The oculars and light source are positioned so that when light reflects from the corneal surface it passes through one of the oculars. The angle of incidence is equal to the angle of reflection. Magnification is set at 15/16X. The angle of the light source 045- 060 and set a parallelpiped beam width.
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This method of illumination is used to observe:
• Details of the pre-corneal film
• Lipids
Tangential Illumination
The oculars are in front of the eyes. The light source is set at 070 - 090. Starts at 10X magnification.
This method of illumination is used to observe:
• the iris and the cornea
• Striae lines and nerve fibres in the cornea
• With a blue filter to observe Fleisher’s ring in Keratoconus
• Pathology of the Iris
• Floaters in the anterior chamber
Parallelpiped Illumination uses a narrow beam of 1 - 2 mm in width.
This method of illumination is used to observe:
• Layers of the cornea and lens to assess depth and extent of corneal abrasions
• Scarring and foreign bodies
Follow the link below to watch a demonstration of the use of parallelpiped illumination. https://www.youtube.com/watch?v=riUS0nMy7P8
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Indirect Focal Illumination
The lamp house is focused on a structure located adjacent to the structure being observed. The lamp house and oculars are set 45°apart. Magnification is set at 16-25X.
This method of illumination is used to observe:
• The Iris
• The corneal epithelium
Sclerotic Scatter
This method of illumination relies on the principle of total internal reflection creating a halo like effect around the limbus. The eyepieces are not used. The surface of the cornea is viewed with the naked eye.
A broad beam of light is focused sharply at the limbus and the oculars are focused on the cornea. The oculars are directly in front of the eye. Start with low magnification. The angle between the oculars and the light source is 045.
This method of illumination is used to observe:
• very subtle corneal changes such as corneal scarring, and corneal edema
• The position and movement of the contact lens.
Retro Illumination
Retro illumination from the iris is created by making a moderately thin slit beam and directing the beam to any internal structure, either the iris, crystalline lens or the retina, at a 45 degree angle and keeping the plane of focus on the cornea. The soft reflected beam from the iris will enhance transparent corneal irregularities that are too subtle to be observed with other lighting situations. Details of corneal changes are best observed in the line between light and dark coming from the unfocused iris surface.
This method of illumination is used for:
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• Studying deposits on Descemet’s membrane
• Vascularization
• Opacities on the crystalline lens
• Epithelial edema
• Delicate scars
Follow the link below to view fluorescein patterns of flat and steep fitting contact lenses. http://www.gpli.info/fluorescein-id-guide
Follow the link below to view the Haag-Streit photo guide of different types of slit lamp illumination. Although this document was created to support the Haag-Streit biomicroscope the techniques used are common to all brands of biomicroscopes.
https://innovamed.com/sites/default/files/downloads/BX900-Photo-guide.pdf
Follow the link below to view an article from the American Academy of Ophthalmology on “How to Use a Slit Lamp”.
https://www.aao.org/young-ophthalmologists/yo-info/article/how-to-use-slit-lamp Follow the link below to view the Efron scale which illustrates the symptoms the contact lens fitter would see with the slit lamp biomicroscope. https://coopervision.com/practitioner/tools-and-calculators/efron-grading-scale#corneal- staining
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Spectacle Magnification/Contact Lens Magnification
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Anisometropia, Anitmetropia and Aniseikonia
• Binocular vision issues caused by the presence of nystagmus, aniseikonia and anisometropia, as well as glare and light sensitivity resulting from aniridia and anisocoria. • High myopic or hyperopic prescriptions if visual improvement (as defined using Snellen acuity) with contact lenses surpasses that which is possible with spectacle wear.
Binocular vision occurs when two eyes with overlapping fields of view work together to form a three-dimensional image on the retina. Sometimes binocular vision cannot be achieved using eyeglasses because of refractive conditions such as Anisometropia or Antimetropia in which different sized images are simultaneously received by the brain and the images cannot be fused into a single image. In the case of Anisometropia both eyes are either hyperopic or myopic but there is a difference in power between the two eyes of 1.50 – 2.00 D. In the case of Antimetropia one eye is hyperopic and the other myopica. The resulting difference in image size is referred to as Aniseikonia.
In these cases when eyeglasses are used as a corrective device the patient experiences an exaggeration of the difference in size due to the phenomenon of Spectacle Magnification. Spectacle Magnification occurs because of the vertex distance from the back of the spectacle lenses to the cornea. Contact lenses are the corrective mode of choice because the vertex distance is eliminated.
Here are examples of Anisometropia.
Example 1 O.D. –2.00
O.S. –4.00
Example 2 O.D +6.00
O.S. +1.00
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If we look at the Example 1:
O.D. -2.00 D
O.S. -4.00 D
The prescription in the O.S. is stronger and based on optics the retinal image produced would be smaller or more minified than the image in the O.D. This is a good example of aniseikonia as there would be a difference in retinal image sizes. The key to a patient obtaining binocular vision is there MUST NOT BE MORE THAN 10% difference between the two images or the brain will be unable to fuse the two images into to one.
Example 2:
O.D. +6.00 D
O.S. +1.00 D
The prescription in the O.D. is stronger and would produce a more magnified or larger image than the O.S. The patient will be unable to obtain binocular vision.
Here is an example of Antimetropia.
For example:
O.D. -6.00 D
O.S. +3.00 D
• The retinal image in the O.D. will be minified.
• The retinal image in the O.S. will be magnified.
Managing Aniseikonia
Only mathematical calculations will allow the Optician to determine if the difference in retinal image sizes is greater than 10%. If that is the case then the Optician must fabricate a pair of aniseikonic eyeglasses or fit contact lenses.
When contact lenses are fitted the elimination of the vertex distance has a profound effect on the retinal image sizes. 28 | P a g e
• Minified images become larger closer to normal size.
• Magnified images become smaller closer to normal size and in most cases, reduce the amount of aniseikonia that affects binocular fusion.
The Spectacle Magnification Formula proves, contact lenses provide better overall vision, and better binocular vision because of less aniseikonia.
Spectacle Magnification Formula
S.M. = 1
1 – aFBVP
a = stands for where corrective lens sits + distance to the entrance pupil (our calculations are in meters).
Note: The entrance pupil distance is calculated from the back surface of the cornea to where the light enters the eye and according to Gullstrand’s schematic eye it is a standard 3mm.
FBVP = power of the lens x Back Vertex Power of the lens.
Note: For accuracy, we always use 4 decimal places for the magnification calculations and the unit of measurement is X’s. For example the result might be expressed as ‘3 X’s magnification’.
EXAMPLE 1 – to use the formula in Eyeglasses vs Contact Lenses
O.D. + 19.50
O.S. + 14.00
Sitting @ 8mm/refracted @ 8 mm
Which would provide better binocular vision for this patient - eyeglasses or contact lenses?
Step 1:
First determine the value for a.
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a = 8 + 3 = 11 mm
The fitted vertex distance provided in the question plus 3 mm to the entrance pupil.
Note: This figure must be converted to metres when inserting into the formula.
Step 2:
Apply the formula.
O.D. O.S.
SM = 1 SM = 1
Glasses 1 – aFBVP Glasses 1 – aFBVP
= 1 = 1
1 – (.011) (+19.50) 1 – (.011) (+14.00)
SM = 1.2731 SM = 1.1820
Step 3:
We want to express the image size as a percentage so we use the percentage formula.
X / Y x 100 = percentage increase.
X = the amount the image is larger than the original (.2731)
Y = the original size (1)
1 / 1.2731 x 100 = 27% 1 / 1.1820 x 100 = 18% 30 | P a g e
We can see the difference in spectacle magnification between the two eyes.
NOTE: You can shorten the calculation by taking the result of the Spectacle Magnification formula, subtracting 1 from that number and then multiplying by 100.
1.2731 -1 x 100 = 27% 1.820 - 1 x 100 = 18%
Step 4:
Next calculate the magnification of retinal image sizes for contact lenses. To do this we must follow the rules of compensative power. We return to the original prescription and note that the eyes were tested at a distance of 8 mm. Using the compensative power formula, we calculate the power of the contact lens on the corneal plane. Remember to convert millimetres to metres.
Fc = F Fc = Compensated Power
1 – dF F = Power stated on the prescription
d = Change in vertex distance expressed in metres
Step 5:
Now that we have calculated the contact lens powers we use the same formula we used to calculate Spectacle Magnification to calculate the magnification of images on the retina if we use contact lenses.
Note: The distance to the entrance pupil for contact lenses is always 3 mm and the contact lens sits on the corneal surface and the corneal surface is only .5 mm thick according to Gulstrand
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CLM = Contact Lens Magnification
O.D. O.S.
CLM = 1 CLM = 1
1 – aFBVP 1 – aFBVP
= 1 = 1
1 – (.003)(+23.00) 1 – (.003) (+15.75)
= ______1______= ______1______
1 - .069 1 - .04725
= ______1______= ______1______
.0931 0.95275
CLM = 1.0741 X’s CLM = 1.0496 X’s
1.0741 -1 x 100 = 7% 1.0496 -1 x 100 = 5%
Step 6:
Now that we’ve worked out the percentage magnification for both spectacles and contact lens we can compare.
The spectacle magnification theory PROVES in cases of refractive error like anisometropia and antimetropia contacts provide better VISION, better binocular vision because of less aniseikonia.
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O.D. O.S.
Retinal Image Size Difference 27 18 (eyeglasses)
Retinal Image Size Difference 7 5 (Contacts)
The difference in magnification between the two eyes in eyeglasses is 9%
(27 – 18). Any difference in image size under 10% is considered acceptable.
BUT contact lenses are much better in terms of providing binocular vision because there is only 2% (7 – 5) difference in image size.
This proves that in cases of anisometropia contact lenses would provide better binocular vision.
For further examples and to practice these calculations go to the Appendix.
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Medications That Affect Contact Lens Wear
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The Effect of Medications on Vision
Opticians are not expected to be medication experts however because certain medications can have a direct impact on the patient’s quality of vision it is useful to know which medications can cause a patients described visual symptoms. For example:
Diuretics can disrupt your normal blood sugar levels. They are taken for a variety of reasons including as part of the drug cocktail for controlling blood pressure. As we have discussed fluctuating blood sugar levels can cause fluctuating vision. Antihistamines are taken to control allergies but can also cause dry eye symptoms leading to blurry or inconsistent vision. Antidepressants are taken to control mood shifts and can cause temporary blurriness. Tetracycline is often prescribed for acne conditions. It too can lead to blurry vision but the patient may also report stinging or redness of the eyes. Birth control pills can lead to dry eye and blurry vision. Corticosteroids are taken for many conditions such as asthma, allergies, arthritis, and skin conditions. The visual symptoms might be light sensitivity, decreased visual acuity and if taken long term can lead to glaucoma or cataracts.
This is by no means an exhaustive list of the effects of drugs on vision but it illustrates why history taking is so important with every patient. And why it’s equally as important that the patient’s medical history continues to be updated at each visit.
Opticians are part of the circle of vision care for their patients. As such Opticians have a responsibility to educate patients and refer to other vision care professionals within the circle of vision care. This places additional emphasis on the importance of having knowledge of vision symptoms that suggest origins related to medications and pathologies of the eye.
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Alcohol Affects on the Eye
Alcohol is not a drug strictly speaking, but it nevertheless does have an impact on vision and contact lens wear. An Optician would use this knowledge if, for example a contact lens patient who had never had such complaints previously reported the following symptoms:
• Oncoming headlights are suddenly more bothersome. Alcohol consumption causes a slower pupil reaction. As a result, light adaptation is slower.
• Contrast sensitivity and depth perception are not as good as they were. The patient is uncertain of how far away the oncoming cars are at dusk.
• The patient complains of eyelid twitching
• The patient complains of having to more frequently use artificial tears to maintain a comfort level. Even a small amount of alcohol can cause or increase dry eye symptoms.
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Environmental Affects on Contact Lens Wear
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Why is Environment Important to the Contact Lens Patient?
It has already been demonstrated in this course that dry eye syndrome is the greatest challenge for the contact lens wearer and for the contact lens fitter. We have examined the physiological factors that are part of the patient’s own ocular system but equally as important are issues such as the climate the patient lives in, where the patient works and the patient’s lifestyle outside of working hours.
Climate and Indoor Conditions
• Contact lens wear is adversely affected by cigarette smoke. Even if the patient is not him/herself a smoker the smoke generated by others is equally as problematic. Cumulative exposure to cigarette smoke can cause damage to the tear surface impacting TBUT.
• Winter weather causes the air to be typically drier than in the summer months. Contact lens fitters must take a different approach to the selection of contact lens modality when fitting patients who live in northern climates. The often high winds associated with winter weather also creates challenges for contact lens wearers.
• Air circulation in homes and workplaces is a contributing factor to contact lens discomfort. That’s true whether it’s air conditioning in summer to keep us cool or warm air circulated by a furnace or fireplace in winter. For example, the patient will be more likely to experience dry eye problems if his/her work station is located directly under the heating/cooling vent.
Digital Eye Fatigue
The abundant use of computer, smart phones and other digital devices leads to Digital Eye Fatigue. This is due to the reduced blink rate that patients experience when they are staring at the device. The symptoms are:
Blurred vision
Tired eyes
Sore eyes
Headaches 38 | P a g e
It’s been found that the average person blinks 18 times per minute under ordinary circumstance but when staring at a computer or digital device that blink rate reduces to 4 times per minute which means the tears are not being flushed over the contact lens and cornea in sufficient volume to keep the environment hydrated.
Digital Eye Fatigue and indoor/outdoor air conditions are just two examples of environmental circumstances that might have to be factored in to the contact lens fitter’s choice of lens modality and fit. For example, the fitter might take a different fitting approach if the patient spends his/her spare time snowboarding or refinishes furniture as a hobby. Unless the patient history includes details of all circumstances under which the patient will be using the contact lenses the contact lens fitter can expect to do some creative problem-solving as he/she continues to care for the patient over time.
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Prescription Interpretation and Ordering
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Prescription Interpretation
Having gathered detailed measurements, assessed comprehensive observations and factored in subjective data provided by the patient the contact lens fitter must make a fitting decision.
The following is a list of helpful hints when analyzing and interpreting a prescription preparatory to fitting a contact lens.
HELPFUL HINTS
1. Refracted cylinders 0.75D or more consider a soft toric or some form of R.G.P.
2. Physiological residual astigmatism (astigmatism remaining after refractive correction has been introduced) or induced residual astigmatism (created by the contact lens/cornea fitting relationship) 0.75D or greater needs to be corrected with either a soft toric or front toric R.G.P.
3. Corneal cylinders up to 2.00D are best corrected with a spherical R.G.P. if the fit is stable or with a soft toric.
4. Corneal cylinders 2.00D or greater are best corrected with a back toric R.G.P. for stability reasons or with a soft toric.
5. Corneal cylinders greater than 2.00D and physiological or induced residual astigmatism 0.75D or greater are better corrected with a bi-toric R.G.P. or a soft toric.
6. The prescription needs to be with-the-rule (WTR) and the “K”s need to be WTR to fit a spherical R.G.P. If not then the only option would be a soft toric.
7. The prescription needs to be against-the-rule (AGT) and the “K”s need to be ATR to fit a spherical R.G.P. If not the only option would be a soft toric.
8. If either the prescription or the “K”s are mixed the only option is a soft toric. 41 | P a g e
9. A spherical prescription and “K” readings that indicate corneal astigmatism present can only be fit with a soft contact lens (ultra thin) to maintain the balance between the corneal and residual astigmatism so that no refracted cylinder is created.
10. Oblique cylinders are best corrected with some form of R.G.P. or soft toric
Follow the link below and read the Contact Lens Spectrum Article called “Correcting Residual Astigmatism”.
https://www.clspectrum.com/issues/2005/april-2005/prescribing-for-astigmatism
Selection of Base Curves
The Optician has now recorded objective and subjective data regarding the patient’s eyes. Now it is time to look at the patient’s prescription and mean “K” readings to determine the correct contact lens for the patient.
For the selection of base curves for soft spherical contact lenses we follow the general rule based on the experience of many contact lens fitters. This is called a ‘rule of thumb’.
• If the mean set of “K” readings is between 42.50 and 44.50, select an average base curve. Either an 8.6/8.7mm depending on the base curve increments determined by the manufacturer. • If the mean set of “K” readings are 44.75mm and greater, select a steep base curve of 8.4/8.3mm • If the mean set of “K” readings are 42.25 and less, select a flat base curve of 8.8/8.9mm
An average set of “K “readings based on the above rule of thumb are just a starting point. The goal is to achieve a good fitting soft contact lens. If the lenses selected using the ‘rule of thumb’ method achieve the goal - no problem. If not then the Optician must re-fit accordingly.
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The criteria of a good fit are: • Good corneal coverage • Good movement • Good corneal integrity • Good visual acuity • Good centration
If the contact lens is fitting too flat then select a steeper base curve If the contact lens is fitting too steep then select a flatter base curve
The determination of whether too flat or too steep is determined by observation through the slit lamp biomicroscope which we will study in another chapter of this course. To observe a soft contact lens the fitter would not use fluorescein since it would absorb into the lens and cause discoloration of the lens. However, fluorescein would be used in assessing the fit of a rigid gas permeable lens.
Signs of a flat soft lens are: • Excessive movement on blink • Lens pops out when performing the ‘push up test’ • Bubbles at the periphery of the lens • Unstable lens rotation Signs of a steep soft lens are: • Limited lens movement on blink • Limited lens movement when performing the ‘push up’ test • Bubbles in the centre of the lens • Vision clears on blink and then gets blurry in between blinks
The ‘push up’ test consists of the contact lens fitter using his/her fingers to push the lower eyelid margin against the lower part of the lens enough to move the lens upward. The contact lens fitter then observes the time it takes for the lens to return to its original position. 43 | P a g e
When adjusting the base curve of a lens to flatten or steepen a lens the contact lens fitter must be careful to consider the refractive power of the modified tear lens.
Base Curve Selection of Other Types of Lenses
Soft toric contact lenses • Base curve selection follows the same rule of thumb fitting as a soft spherical contact lens.
Rigid gas permeable contact lenses • In order to fit these contact lenses the Optician needs to follow the nomogram (fitting chart) recommended by the manufacturer and evaluate the fitting with fluorescein.
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Final Lens Selection
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Final Lens Order
The Optician is responsible for ordering the contact lenses specifications unless it is a complicated contact lens fitting and then the lens can be ordered empirically and then those contact lenses become the trial contact lens that may or may not exhibit the criteria of a good fitting contact lens.
Prescription Interpretation Examples
Example 1:
Patient presents with the following prescription: • O.D. -6.00 -4.00 X 180 “K” readings 42.00@ 180 / 43.00@ 090 • O.S. -3.50 -2.00 x 180 “K” readings 43.00@ 180 / 44.00@ 090
Based on your review of the Helpful Hints document, what type of contact lens would you recommend for this patient?
Here is the thinking process and analysis of the information.
Check first to make sure the prescription and mean “K’s are with the rule (WTR) or against the rule (ATR). A prescription in minus cylinder form will have its axis at 180° (– cyl x 180). If the patient is a myope the greatest refractive power lies in the 090° meridian. The opposite is true for the hyperope.
In our example: O.D. Rx: -6.00 -4.00 x 180 This is an example of WTR as it is minus cylinder axis 180 and the power is the greatest in the 090° meridian. (-10.00)
“K”: 42.00 @180 / 43.00 @ 090
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This is an example of WTR “K”s as the flattest meridian is in the 180 meridian.
Therefore both the prescription and “K”s are WTR.
O.S. Rx: -3.50 -2.00 x 180 “K”s: 43.00 @ 180 / 44.00 @ 090 T
The prescription is WTR The “K”s are WTR
Next step is to look at the refracted cylinder (which is in the prescription from the refractionist) and determine whether it is due to physiological or lenticular astigmatism.
Physiological astigmatism can only come from two places within the eye: Either the cornea, the crystalline lens (called lenticular astigmatism) or a combination of both. When the astigmatism comes from the cornea it will show up in the difference in “K” readings. The rest of the astigmatism has to come from inside the eye. When the astigmatism comes from inside the eye we always assume it is lenticular but just to note that it could also come from the back surface of the cornea or misalignment of the optical axis of the eye from the macula fovea.
In our example: • O.D. has a refracted cyl of 4.00 D, the difference in “K”s indicate that 1.00 D came from the corneal surface and a remaining 3.00 D came from inside the eye. • O.S. has a refracted cyl of 2.00 D, the “K”s indicate that 1.00 D came from the corneal surface and the remaining 1.00 D came from inside the eye
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Now we are ready to select our first choice of lens
O.D. Selection: FRONT TORIC R.G.P. As the tear layer will correct the one dioptre of corneal cylinder and the cylinder on the front will take care or the astigmatism inside the eye. This is the first choice based on providing the patient with the best visual acuity
O.S. Selection: FRONT TORIC R.G.P. As the tear layer will correct the one dioptre of corneal cylinder and the cylinder on the front will take care of the astigmatism inside the eye. This is the first choice based on providing the patient with the best visual acuity.
As a second choice, you could also fit this patient with a soft toric contact lens.
Example 2: A patient presents with the following prescription and “K” readings: NOTE: Use “HELPFUL HINTS” to work out your answer.
O.D.
RX: plano -1.00 x 090
“K”s 43.00 @ 180 / 42.00 @ 090
RX and “K”s are against the rule
Refracted cylinder of 1.00 D comes from the corneal surface
O.S.
Rx: -2.00 -2.75 x 060
“K”s 43.75 @ 150 / 41.50 @060
2.25 D of the refracted cylinder comes from the corneal surface. 48 | P a g e The remaining 0.50 D comes from inside the eye. (It is less than 0.75 D
and will not affect patient’s V.A.) What type of contact lens would be your first choice for this patient?
Explanation: This is a classic case that lends itself to fitting an R.G.P. contact lens.
In the O.D. both the prescription and “K”s are A.T.R. which means the tear lens will be created in the correct meridian. The O.S. has a prescription and “K”s that are oblique and the best method of contact lens correction is an R.G.P.
Two soft torics would be a second choice but noting that stability is sometimes an issue on oblique cylinders.
Example 3 A patient presents with the following prescription and “K” readings: NOTE: Use “HELPFUL HINTS” to work out your answer.
O.D.
Rx: +3.00 +2.00 x 090
“K”s 42.00 @180 / 44.00 @ 0090 RX needs to be transposed:
+5.00 -2.00 x 180
Rx and “K”s are with the rule All refracted cylinder is corneal
O.S.
Rx: +6.00
“K”s 43.00 @180 / 47.00 @ 090
No refracted cylinder
4.00 D of with the rule corneal astigmatism
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What type of contact lens would be your first choice for this patient?
Explanation: The O.D. has a refracted cylinder of 2.00D and it must be corrected. The O.S. has no refracted cylinder but a large amount of corneal cylinder. But we must maintain that balance so a thin spherical lens is needed. An R.G.P. cannot be fit on this patient. Therefore the O.D. is a soft toric and the O.S. is a thin soft contact lens.
Example 4:
A patient presents with the following prescription and “K” readings: NOTE: Use “HELPFUL HINTS” to work out your answer
O.D.
Rx: -10.00 -1.50 x 180
“K”s 42.50 @ 180 / 44.00 @ 090
Both Rx and “K”s are with the rule
Refracted cylinder comes from the
O.S.
RX: -6.50
“K”s: 42.00 @ 180 / 44.00 @ 090
No refracted cylinder
2.00 D of corneal cylinder
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What type of contact lens would be your first choice for this patient?
Explanation: The O.D. exhibits the ‘four to one rule’ and has a 1.50 D refracted cylinder which should be corrected. So, there are several choices for this example. The O.S. needs a thin soft contact lens in order to maintain the balance that naturally was created. The first choice is O.D. soft toric contact lens and O.S. soft thin spherical contact lens Second choice is O.D. a spherical equivalent contact lens and O.S. a soft thin spherical contact lens.
Example 5:
O.D. Rx: -6.00 -4.00 x 180 “K”s: 44.00 @ 180 / 48.00 @ 090
O.S. Rx: -3.50 -2.00 X 180 “K”s: 44.00 @ 180 / 46.00 @ 090
What type of contact lens would be your first choice for this patient? Then if applicable what would be your second choice?
Explanation: First choice O.D. Back toric rigid gas permeable contact lens , perhaps even a bi-toric rigid gas permeable O.S. Spherical rigid gas permeable contact lens.
Second choice O.D. Soft toric contact lens O.S. Soft toric contact lens
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Example 6: O.D. Rx: -4.50 -4.00 X 180 “K”S: 43.00 @ 180 / 43.00 @ 090
O.S. Rx: -2.00 -1.00 X 180 “K”s: 42.00 @ 180 / 43.00 @ 090
What type of contact lens would be your first choice for this patient? Then if applicable what would be your second choice?
Explanation: First choice O.D. Front toric rigid gas permeable contact lens O.S. Spherical rigid gas permeable contact lens
Second choice O.D. Soft toric contact lens O.S. Soft toric contact lens
Example 7:
O.D. Rx: -2.50 “K”s: 43.00 @ 180 / 46.00 @ 090
O.S. Rx: -7.25 “K”s: 43.00 @ 180 / 47.00 @ 090
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What type of contact lens would be your first choice for this patient? Then if applicable what would be your second choice?
The first and only choice in this case is • O.D. Thin soft contact lens • O.S. Thin soft contact lens
Example 8: O.D. Rx: + 3.50 + 2.00 x 090 “k”s: 41.00 @ 180 / 43.00 @ 090
O.S. Rx: +2.50 +1.00 x 090 “ 41.00 @ 180 / 42.00 @ 090
What type of contact lens would be your first choice for this patient? Then if applicable what would be your second choice?
Explanation: First choice O.D. Spherical rigid gas permeable contact lens O.S. Spherical rigid gas permeable contact lens Second choice O.D. Soft toric contact lens O.S. Soft toric contact lens
Manifest Over-Refraction
The final procedure before making a final lens selection/order is to perform a manifest over-refraction.
Manifest over-refraction is a process of using lenses from an optical trial set or using a phoropter to evaluate visual acuity with corrective lenses in place on the patient. Once a trial lens has been inserted and equilibration has taken place the
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contact lens fitter confirms the accuracy of the fit of the lens and then performs an over-refraction to determine if additional power is required.
The procedure is performed both monocularly and binocularly using +/- spheres in the case of spherical corrections and sphero-cylindrical corrections where the difference in ‘K’s of 0.35 mm or more. Where the difference in ‘K’ readings is greater than 0.35 mm a toric over-refraction must be performed.
Follow the link below for a short article on one practitioner’s use of over-refraction. https://www.clspectrum.com/issues/2007/june-2007/the-contact-lens-exam
Follow the link below to view a video on performing a toric over-refraction. https://www.youtube.com/watch?v=gaD3G3gVO3s
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Training on Insertion, Removal and Continuing Care
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The Importance of Patient Education
Every time the contact lens fitter sees the patient, from the first intake session and continuing through every follow-up visit is an opportunity to provide patient education about ways to protect vision and eye health. Usually the patient will return for follow-up visits and the contact lens fitter will have the opportunity to monitor compliance and assess the impact of the contact lens on the cornea. But we do live in an age where more and more patients turn to the Internet for purchases of replacement lenses. The fitter may not see the patient again until there is a problem to be solved.
As well, there is a limit to how much information the patient can absorb during the fitting process. The contact lens fitter has to make sure all essential insertion, removal, care and handling information is delivered when the contact lenses are dispensed.
The contact lens fitter must also be pro-active about organizing follow-up appointments with the patient. It is during the follow-up appointments that the contact lens fitter, using subjective feedback from the patient and objective assessment of the contact lens, the cornea and adnexa that the contact lens fitter can correct patient misunderstandings and reinforce or change patterns of behaviour.
Training of Insertion and Removal of Contact Lenses
The contact lens fitter must coach the patient in insertion and removal techniques using demonstration techniques as well as providing written material for the patient. Because we live in a multi-cultural country it is important to be aware of the dominant ethnic groups in the catchment area of the dispensary and provide written literature in that language.
This part of the dispensing protocol allows the Optician to teach a skill but – and this is equally important – educate the patient about why it is important to incorporate the correct insertion, removal, wearing schedule and hygiene regimen into his/her routine. The Optician must make sure the patient understands the potential consequences of not up taking this responsibility. 56 | P a g e
It is useful to provide multi-media instructions to patients where possible. Because the use of electronic hand-held devices is so universal the contact lens fitter could save the following links (one on insertion and removal of soft lenses and the other on the insertion and removal of RGP lenses) on his/her smart phone and use them as another training tool. https://coopervision.com/practitioner/build-your-practice/video-library/application- and-removal-contact-lenses https://www.youtube.com/watch?v=1hP44Sr7pU8
Solutions Opticians are responsible to recommend the appropriate contact lens solutions for the patient, modality of contact lens wear and contact lens material. There are many brands of solutions available today but the contact lens fitter must find the solution that is best for a specific patient’s needs. A solution that works well for one patient may not work as well for another.
A Solution Must Have: • A good surfactant cleaner • A good wetting agent • A good disinfectant • A good buffering agent
From the patient’s point of view the solution must be: • Cost effective and • Easy to use
It is best practice to provide the patient with a starter kit of a recommended solution however the effectiveness of the solution and the compatibility of the solution with the patient’s physiological and lifestyle needs must be reviewed at each follow-up visit.
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Follow the link below and read this excellent article “Does One Contact Lens Solution Fit All?” http://www.reviewofcontactlenses.com/content/c/28321
Equilibration and Adaptation
Equilibration and adaptation are two totally different parts or the fitting process. Equilibration is what takes place at the beginning of the fitting process when the contact lens fitter first installs the lens. Adaptation takes places as the patient begins to build up wearing time.
• Equilibration can take from 20/30 minutes with any soft contact lens and is a necessary step in the fitting procedure before evaluation with the slit lamp biomicroscope. The soft contact lens needs to settle and become accustomed first to the change in temperature. (Room temperature when the soft contact lens was stored to the eye which has a higher temperature) and secondly to the amount of tear provided by the eye. When the soft contact lens are stored the lens is usually 100% hydrated but when placed in the eye it dehydrates slightly as it settles and that is why the Optician needs time to let the soft contact equilibrate.
• All types of rigid gas permeable contact lenses must also equilibrate but not necessarily for the same reasons. The patient needs to get accustomed to the feel of the rigid contact lens and that may take 20/30 minutes also. The patient should sit with the eyes looking down until such time they are able to look straight ahead comfortably with reduced tearing then fluorescein can be applied and the fitting assessed using the slit lamp biomicroscope.
• Adaptation is very fast with all types of soft lens materials. If fitting a multifocal soft contact lens neural adaption must take place and it can take up to two weeks for the brain to adapt to multiple overlapping images (simultaneous imagery) on the retina. Rigid lenses will also take weeks to totally adapt.
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Explanation of Normal Adaptive Symptoms
Before leaving the dispensary for the first time with the contact lenses the patient must be made aware of normal adaptive symptoms because they otherwise might stall in building up their wearing time.
Normal adaptive symptoms include the following: • Tearing • Contact lenses feeling uncomfortable at times • Some blurred vision • Some double vision • Some problems reading • Eyes may become red • Eyes may feel itchy • Solutions may sting or burn a little upon insertion of the lens
All normal symptoms should go away as the patient becomes adapted to their contact lenses. If the symptoms do not go away then the Optician needs to problem solve until the symptoms do go away.
Follow the link below. It provides a patient-oriented overview of all things related to insertion, removal, hygiene and includes a section on normal symptoms and symptoms that require urgent care. http://opticians.bc.ca/contact-lens-wear-and-care-soft-lenses
Wearing Schedule
Opinions on recommended wearing schedule may vary slightly from Optician to Optician but at the end of the day the patient must become accustomed to the feel of the contact lens and the cornea accustomed to receiving oxygen at a different rate which must not affect the corneal metabolism. The following are typical recommendations.
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SOFT SPHERICAL AND SOFT TORIC CONTACT LENSES • Wear the contact lenses for four hours the first day • Increase two hours every day until full time wear is achieved, an average of 14 hours per day
RIGID GAS PERMEABLE CONTACT LENSES • Wear the contact lenses for five hours a day for the first week • Increase two hours every day until full time wear is achieved (an average of 14 hours per day).
Follow Up and Aftercare Requirements
1. The patient should bring contact lens solution to the follow-up appointment to make sure the patient is still using the solution that was recommended. The patient should also bring his/her eyeglasses to the appointment in case the contact lens fitter has to instill fluorescein or for some other reason the patient cannot put the lenses back in.
2. Test Visual Acuity with eyeglasses and with contact lenses.
3. The patient should be questioned to determine how the contact lens is fitting from their perspective. These are called subjective responses. Examples of questions would be • How many hours a day do you wear the contact lenses? • Are they comfortable? • When you remove your contact lenses and wear your eyeglasses how is your vision? • Do you have any questions regarding cleaning or looking after your contact lenses? 4. Contact lenses must be worn for at least two to four hours prior to a check up to allow any symptoms to be noticeable to the Optician.
5. Visual acuity assessment must be performed at every check up.
6. Over keratometry can be performed while the patient is wearing soft contact lenses to assess the fitting. 60 | P a g e
7. A Slit lamp evaluation with the lenses in “situ” to verify the fitting stability of the lenses. Perform a second slit lamp evaluation without the lenses using different methods of illumination to verify the maintenance of corneal integrity.
8. Evaluate the position of a toric lens, is it in the same position as the last visit or the trial lens evaluation
9. Ask the patient to demonstrate the insertion and removal of a contact lens
10. Review the solution regime with the patient
11. Review the wearing schedule and aftercare appointments
On average a patient must be seen on a regular basis in order to maintain ocular health
A RECOMMENDED SCHEDULE IS: • After the first week • Second week • One month • Three months • Six months • Once a year • For ever
Conclusion In this course, we have followed the contact fitter through the process of patient intake to final dispensing. We have reviewed the data that must be collected and recorded including:
• The medical and optical history • The relevant environmental and pharmaceutical-related issues 61 | P a g e
• The measurements and assessments • The instruments used • The interpretation of the measurements taken and readings made • The prescription analysis including anomalies that affect fitting decisions • The rationale for fitting decisions made
Best practice for any health care professional is to establish and follow a strict routine. There are many variables at work in achieving a successful contact lens fit. It is easy to overlook some of the detailed tasks unless you follow each step for each patient at every follow-up visit.
For example, the patient may not complain of or be displaying any symptoms of conjunctivitis but if you evert the upper lid you may detect early onset symptoms and be able to prevent further symptoms.
The best contact lens fitters continue to observe, to inquire and to pro- actively seek answers to challenges presented to them by their patients. Careful attention to details, reflection on an accumulation of fitting experiences and making a life-long commitment to learning lead to creating a fulfilling practice dedicated to patient care.
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Appendix
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Here are some examples of the calculations performed in comparing Spectacle Magnification to Contact Lens Magnification in a series of prescriptions
Example #1
O.D. + 11.75 D
O.S. + 19.25 D
Eyeglasses
This prescription was tested and fitted at 12 mm.
O.D. O.S.
SM = 1 SM = 1
Glasses 1 – a FBVP Glasses 1 – aFbvp
= 1 = 1
1 – (.015) (+11.75) 1 – (.015) (+19.25)
SM = 1.2140 X magnification SM = 1.4060 X magnification
1.2140 -1 x 100 = 21% 1.4060- 1 x 100 = 41%
This should create a problem with obtaining binocular vision for the patient with the eyeglasses as there is 20 % difference between the retinal image sizes.
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Contact Lenses
O.D. compensative power O.S. compensative power
Fc = F Fc = F
1 – dF 1 – dF
= + 11.75 = + 19.25
1 – (+.012) (+11.75) 1 – (+.012) (+19.25)
= + 13.68 D = +13.75D = + 25.03 D = +25.00D
SM = 1 SM = 1
Contacts 1 – aFbvp Contacts 1 – aFbvp
= 1 = 1
1 – (.003) (+13.75) 1 – (.003) (+25.00)
CLM = 1.0430 X magnification CLM = 1.0812 X magnification
1.0430 – 1 x 100 = 4% 1.0812 -1 x 100 = 8%
Contacts are better as there is less aniseikonia resulting in a better chance of binocular vision.
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O.D. O.S.
Retinal Image Size Difference 21 41 (Glasses)
Retinal Image Size Difference 4 8 (Contacts)
Aniseikonia with eyeglasses = 20%
Aniseikonia with contact lenses = 4%
The Opticians responsibility is to recognize ametropic conditions that may result in the patient having difficulty obtaining binocular vision and therefore to recommend contact lenses first as well as a back-up pair of aniseikonic eyeglasses.
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Example 2
O.D. +6.00 D
O.S. – 2.00 D
O.D. O.S.
SM = 1 SM = 1
Glasses 1 – aFbvp Glasses 1 – aFbvp
= 1 = 1
1 – (.013) (+6.00) 1 – (.013) (-2.00)
SM = 1.0846 X magnification SM = 0.9747 X magnification
(notice here the magnification is greater (notice here that the minification is less than 1 which is considered normal as all than 1 which is considered normal as all plus lenses create magnified images) minus lenses create minified images.)
1.0846 -1 x 100 = 8% 0 .9747 -1 x 100 = -3%
The tested and fitted distance is 10 mm.
Magnification of the retinal image is happening in the O.D. and minification of the retinal image is happening in the O.S.
Aniseikonia difference equal to 11%.
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Now let’s look at contact lenses.
First, we need to compensate the power in the O.D.
O.D. compensative power O.S. compensative power
Not required
Fc = F
1 – dF
= + 6.00
1 – (+.010) (+6.00)
= + 6.38 D = +6.50 D
SM = 1
Contacts 1 – aFbvp SM = 1
Contacts 1 – aFbvp
= 1
1 – (.003) (+6.50) = 1
1 – (.003) (-2.00)
CLM = 1.0199 X magnification CLM = 0.9940 magnification
1.0199 – 1 x 100 = 2 % 0.9940 -1 x 100 = -1%
Fitting contact lenses on this patient with antimetropia results in a reduction in retinal image size in the O.D. and an increase in size in the retinal image of the O.S.
The aniseikonia is equal to 3% proving again the best correction for this patient would be contact lenses that would provide binocular vision.
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SELF ASSESSMENT
1. Explain why it is possible to dispense a contact lens to a monocular aphake but not a pair of eyeglasses, especially when the other eye has good visual acuity. O.D. +15.00D O.S. Plano
Fitted and tested vertex distance 12 mm (Please explain in the form of a few sentences, as well as mathematical calculations.)
2. A patient has the following prescription:
O.D. + 10.50 O.S. + 11.50 +3.00 X 180
Calculate:
a) The compensative power for a pair of eyeglasses that are refracted at 12 mm and fitted at 8 mm b) Would there be a problem obtaining binocular vision with eyeglasses for this patient. c) Would contact lenses be better for this patient?
In summary and conclusion, it is the Opticians responsibility to recognize potential
problems by analyzing the prescription thoroughly and then by recommending the
correct optical device.
Answer to these self-assessment questions can be found on the following pages.
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Self Assessment Answer Sheet
Question #1
O.D. O.S. Normal vision
SM = 1
Glasses 1 – aFbvp
= 1
1 – (.015) (+15.00)
SM = 1.2903 X magnification
= 1.2903 -1 x 100 = 29 %
Therefore, with eyeglasses there is a difference of 29% in retinal image size.
O.D. Compensative power
Fc = F
1 – dF
= + 15.00
1 – (+.012) (+15.00)
= + 18.29 D = +18.25 D
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SM = 1
Contacts 1 – a FBVP
= 1
1 – (.003) (+18.25)
SM = 1.0579 X magnification
1.0579 – 1 x 100 = 6%
Therefore, with a contact lens the aniseikonia is reduced to 6%
In summary, a monocular aphake would have a better chance of obtaining binocular vision fitted with one contact lens. This is the number one optical correction for this situation.
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Question #2
O. D. Compensative power
Fc = F
1 – dF
= + 10.50
1 – (+.004) (+10.50)
= + 10.96 D = +11.00 D
O.S. Compensative power -
Note: Use meridian of greatest power as it will determine the greatest retinal image size to calculate the induced aniseikonia.
Fc = F
1 – dF
= + 14.50
1 – (+.004) (+14.50)
= + 15.39 D = +15.50 D
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O.D.
SM = 1
Glasses 1 – aFbvp
Remember the eyeglasses are sitting at 8mm
= 1
1 – (.011) (+11.00)
SM = 1.1377 X magnification
1.1377 -1 x 100 =14 %
O.S
SM = 1
Glasses 1 – aFbvp
Remember the eyeglasses are sitting at 8mm
= 1
1 – (.011) (+15.50)
SM = 1.2055 X magnification
1.2055 -1 x 100 =21 %
The aniseikonia induced due to the eyeglasses is 7%. This is still within the tolerance of 10% but contact lenses will prove to be the better choice.
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Typically, as a contact lens fitter to compensate for the contact lens power please return to the original prescription.
O. D. Compensative power
Fc = F
1 – dF
= + 10.50
1 – (+.012) (+10.50)
= + 12.01 D = +12.00 D
O.S . Compensative power
Fc = F
1 – dF
= + 14.50
1 – (+.012) (+14.50)
= + 17.55 D = +17.50 D
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O.D.
SM = 1
Contacts 1 – aFbvp
Note: Remember that contact lenses are on the corneal surface
= 1
1 – (.003) (+12.00)
SM = 1.0373 X magnification
1.0373 -1 x 100 = 4 %
O.S.
SM = 1
Contacts 1 – aFbvp
Remember that contact lenses are on the corneal surface
= 1
1 – (.003) (+17.50)
= 1.0554 X
1.0554 -1 x 100 = 6 %
The aniseikonia induced due to contact lens wear is 2% proving again that the best method of correction for anisometropia or antimetropia is contact lenses because they enhance binocular vision.
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End Notes
i Diabetic corneal neuropathy.
R O Schultz, M A Peters, K Sobocinski, K Nassif, K J Schultz
Trans Am Ophthalmol Soc. 1983; 81: 107–124
ii Corresponding author: Angelo Avogaro, [email protected].
Diabetes Care 2011 May; 34(Supplement 2): S285-S290. https://doi.org/10.2337/dc11-s239
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