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Introduction Subtend Minimum Detail Resolution 11/4/2019 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 12 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 34 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 eye 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 56 1 11/4/2019 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 78 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 910 Snellen Letters Minimum Angle of Resolution 11 12 2 11/4/2019 Landolt Ring (C) and the Illiterate E 13 14 Contrast Sensitivity 15 16 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 17 18 3 11/4/2019 Terminology Anatomy Presbyopia Aqueous humor Greek Presby = Old Opia = Sight 19 20 Four Refractive Mediums of the Eye Anatomy The cornea The aqueous humor The crystalline lens The vitreous humor Cornea Aqueous humor Crystalline lens Vitreous humor 21 22 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 23 24 4 11/4/2019 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 25 26 Ametropia Myopia ‐ Near Sighted ‐ Short Sight •Myopia •Hyperopia or Hypermetropia •Astigmatism 27 28 Myopia ‐ Near Sighted ‐ Short Sight Myopia ‐ Near Sighted ‐ Short Sight 29 30 5 11/4/2019 Hyperopia ‐ Farsighted ‐ Long sight Hyperopia ‐ Farsighted ‐ Long sight 31 32 Hyperopia ‐ Farsighted ‐ Long sight Astigmatism 33 34 Astigmatism Astigmatism Corneal astigmatism Simple myopic Lenticular astigmatism astigmatism Regular astigmatism Compound myopic Irregular astigmatism astigmatism Simple hyperopic astigmatism Compound hyperopic astigmatism Mixed astigmatism 35 36 6 11/4/2019 Corneal Astigmatism Lenticular Astigmatism 37 38 Regular Astigmatism Types of Regular Astigmatism Simple myopic astigmatism Compound myopic astigmatism Simple hyperopic astigmatism Compound hyperopic astigmatism Mixed astigmatism 39 40 Simple Myopic Astigmatism Compound Myopic Astigmatism 41 42 7 11/4/2019 Simple Hyperopic Astigmatism Compound Hyperopic Astigmatism 43 44 Mixed Astigmatism Irregular Astigmatism 45 46 Astigmatism Astigmatism 47 48 8 11/4/2019 Cylindrical Lenses Terminology Cylinder Lenses Presbyopia Toric Lenses Sphero‐Cylindrical Lenses Greek Flat and Toric Transposition Presby = Old Spherical Equivalent Opia = Sight Contact Lenses 49 50 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 51 52 Change in the Mean Amplitude of Accommodation With Age Corrections for Presbyopia Age (Years) Amplitude (Diopters) Rx reading glasses 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) 53 54 9 11/4/2019 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 55 56 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 57 58 Muscle Imbalances ‐ Terminology Muscle Imbalances ‐ Terminology Eso‐ Tonicity Exo‐ Fusion Hyper‐ Diplopia Hypo‐ ‐phoria ‐tropia 59 60 10 11/4/2019 Muscle Imbalances ‐ Terminology Treatment Orthophoria Glasses Patching Heterotropia Surgery Strabismus ‐ Can lead to Lazy eye or Vision Therapy Amblyopia 61 62 Exotropia Esotropia (divergent squint) Eye turned out Wall eyes (convergent squint) Eye turned in Cross‐eyed Boss‐eyed 63 64 Hypertropia Hypotropia (vertical) Eye turned up (vertical) Eye turned down 65 66 11 11/4/2019 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 67 68 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 69 70 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 71 72 12 11/4/2019 Analyzing and Interpreting the Rx Visualization of Rx Concave Lenses What we see Convex Lenses Contact Lenses What the patient sees 73 74 Your Prescription Conclusion Sphere Cylinder Axis Thank you OD -2.25 -1.50 180 OS +3.75 +1.50 090 ADD OU +2.25 75 76 13.
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