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Introduction  Terminology  Presbyopia  Anatomy  Muscle Imbalances  Refractive Errors  Unequal refractive errors  Spherical Correction  Visualizing the Rx  Cylindrical Correction

By Diane F. Drake, LDO, ABOM, NCLEM, FNAO

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Visual Angle and Minimum Visual Angle Subtend Minimum Visual Angle  To extend under or to be opposite to  The angle which is opposite the object being observed

Visual Angle

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Resolution Minimum Detail  The ability to detect  The detail that must be detected on an object to minimum detail positively identify or distinguish the object  The resolving power of the normal is a minimum E visual angle of 1 minute  The minimum visual angle of the letter is 1 minute Minimum Detail  The visual angle of the letter is 5 minutes E Minimum Detail

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Visual Acuity Snell’s Law of Refraction

 The measure of the angle subtended by the outer  n1 sin i = n2 sin r limits of rays of light coming from the minimum detail of an object as they enter the eye

 20/20 or 6/6

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The Snellen Fraction Snellen Letters  The distance at which the test is made divided by the distance at which the smallest letter read subtends an angle of 5 minutes

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Snellen Letters Minimum Angle of Resolution

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Landolt Ring (C) and the Illiterate E

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Contrast Sensitivity

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Terminology Terminology  Astigmatism  Simple myopic  Emmetropia  Corneal astigmatism astigmatism  Ametropia  Lenticular astigmatism  Compound myopic  Myopia  Regular astigmatism astigmatism   Hyperopia  Irregular astigmatism Simple hyperopic astigmatism  Compound hyperopic astigmatism

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Terminology Anatomy  Presbyopia

Aqueous humor  Greek  Presby = Old  Opia = Sight

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Four Refractive Mediums of the Eye Anatomy  The  The aqueous humor  The crystalline lens  The vitreous humor Cornea Aqueous humor Crystalline lens

Vitreous humor

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Index of Refraction Dioptric Power  Cornea = 1.37  Cornea  Aqueous humor = 1.33  +42.00D to +45.00D  Performs about 80% of the refraction or bending of light  Crystalline lens = 1.42 rays within the eye  Vitreous humor = 1.33  Crystalline Lens  +12.00 to +15.00D  +20.00 D

 Depending on textbook

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Refraction  The “bending” of light as it passes obliquely between Emmetropia two different refractive mediums

 A beam of light that enters a refractive medium perpendicularly is not refracted, but merely slowed down and the path of the beam is unchanged

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Ametropia Myopia ‐ Near Sighted ‐ Short Sight

•Myopia •Hyperopia or Hypermetropia •Astigmatism

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Myopia ‐ Near Sighted ‐ Short Sight Myopia ‐ Near Sighted ‐ Short Sight

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Hyperopia ‐ Farsighted ‐ Long sight Hyperopia ‐ Farsighted ‐ Long sight

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Hyperopia ‐ Farsighted ‐ Long sight Astigmatism

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Astigmatism Astigmatism  Corneal astigmatism  Simple myopic  Lenticular astigmatism astigmatism  Regular astigmatism  Compound myopic  Irregular astigmatism astigmatism  Simple hyperopic astigmatism  Compound hyperopic astigmatism  Mixed astigmatism

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Corneal Astigmatism Lenticular Astigmatism

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Regular Astigmatism Types of Regular Astigmatism  Simple myopic astigmatism  Compound myopic astigmatism  Simple hyperopic astigmatism  Compound hyperopic astigmatism  Mixed astigmatism

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Simple Myopic Astigmatism Compound Myopic Astigmatism

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Simple Hyperopic Astigmatism Compound Hyperopic Astigmatism

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Mixed Astigmatism Irregular Astigmatism

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Astigmatism Astigmatism

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Cylindrical Lenses Terminology  Cylinder Lenses  Presbyopia  Toric Lenses  Sphero‐Cylindrical Lenses  Greek  Flat and Toric Transposition  Presby = Old  Spherical Equivalent  Opia = Sight  Contact Lenses

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Presbyopia Understanding Presbyopia  Causes  Age‐Related Vision Changes  Treatment As we age, our visual system undergoes major changes  Spectacles  Contact Lenses  Decline of accommodation  Senile miosis  Loss of visual acuity  Lowered contrast sensitivity  Increased lighting sensitivity  Slower speed of visual processing

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Change in the Mean Amplitude of Accommodation With Age Corrections for Presbyopia Age (Years) Amplitude (Diopters)  Rx reading  Surgery 10 10.6 ‐ 13.5  OTC readers  Explain limitations to 15 10.1 ‐ 12.5  your patients 20 9.5 ‐ 11.5 PAL’s 30 6.6 ‐ 8.9  Segmented lenses  Others 35 5.8 ‐ 7.3  Contacts (Soft and Rigid) 40 4.4 ‐ 5.9 45 2.5 ‐ 3.7  Mono 50 1.6 ‐ 2.0  Bifocals 55 1.1 ‐ 1.3  Modified 60 0.7 ‐ 1.0 Measured by moving the target toward the subject until first blur is reported (Borish 1970; Turner 1958)

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Muscle Imbalances The bony orbit  Terminology  Quadrilateral pyramid  Muscles of the Eye  Possible Corrections  Influenced by age, trauma, as well as chronic sinus infections.

 Bed ridden, non‐mobile person

 Contain the muscles of the eye

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Extraocular Muscles

Extraocular Muscles  Superior Rectus  Moves the eye up  Medial rectus (MR)—moves the eye toward the nose  Superior Oblique  xternal rectus (ER)—moves the eye away from the nose  Rotates the eye so that the top of eye  Superior rectus (SR)—primarily moves the eye upward and moves toward nose secondarily rotates the top of the eye toward the nose  Medial Rectus  Inferior rectus (IR)—primarily moves the eye downward and  Moves eye toward nose secondarily rotates the top of the eye away from the nose  Lateral Rectus  Moves eye away from nose  Superior oblique (SO)—primarily rotates the top of the eye toward  Inferior Rectus the nose and secondarily moves the eye downward  Moves the eye down  Inferior oblique (IO)—primarily rotates the top of the eye away  Inferior Oblique from the nose and secondarily moves the eye upward  Rotates the eye so that the top of eye moves away from nose

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Muscle Imbalances ‐ Terminology Muscle Imbalances ‐ Terminology Eso‐ Tonicity Exo‐ Fusion Hyper‐ Diplopia Hypo‐ ‐phoria ‐tropia

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Muscle Imbalances ‐ Terminology Treatment Orthophoria  Glasses  Patching  Heterotropia  Surgery  ‐ Can lead to Lazy eye or  Vision Therapy Amblyopia

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Exotropia Esotropia (divergent squint) Eye turned out Wall (convergent squint) Eye turned in Cross‐eyed Boss‐eyed

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Hypertropia Hypotropia (vertical) Eye turned up (vertical) Eye turned down

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Anisometropia Anisometropia  “unequal measure”  Example Rx:  The condition when the two eyes require a OD ‐7.00 D. sphere different degree of correction (1.00 or more) but OS ‐3.00 D. sphere the same kind of correcting lens (+ or ‐)  The condition may cause vertical prism  Example Rx: imbalance at near or cause a difference in the OD +7.25 sphere retinal image sizes between the two eyes OS +5.25 sphere

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Antimetropia Antimetropia  “opposite measure”  Example Rx:  The condition when the two eyes require opposite OD +1.75 sphere kinds of corrective lenses (+ or ‐) OS ‐1.00 sphere  The condition may cause vertical prism imbalance at near or cause a difference in the retinal image  Example Rx; sizes between the two eyes OD ‐2.25 sphere OS +1.50 sphere

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Aniseikonia Iseikonic lenses  “unequal images”  Anisometropia or antimetropia may result  A lens or pair of lenses used to correct aniseikonia in the condition whereby two unequal images are sent by the eyes to the brain  The following variables are used:  More prevalent due to refractive surgeries  Base curve

 Meridional Aniseikonia  Thickness  Normal or less aniseikonia in one meridian and more  Vertex distance in another due to high astigmatism in that meridian  Index of refraction

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Analyzing and Interpreting the Rx Visualization of Rx  Concave Lenses  What we see  Convex Lenses  Contact Lenses  What the patient sees

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Your Prescription Conclusion

Sphere Cylinder Axis Thank you OD -2.25 -1.50 180 OS +3.75 +1.50 090

ADD OU +2.25

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