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Contrast sensitivity, Clinical assessment of intra-ocular light scatter, recovery from glare (macular photo stress test)


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  • Multiple sclerosis (MS) is a chronic autoimmune disorder affecting movement, ensation, and bodily functions. It is caused by destruction of the myelin insulation covering nerve fibers (neurons) in the central nervous system (brain and spinal cord)
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    • 1. Contrast sensitivity, Clinical assessment of intra-ocular light scatter, Dark adaptation, recovery from glare (macular photo stress test) Mohammad Arman Bin Aziz Optometry Officer ICO, CU March 20, 2014
    • 2. Contrast • The ratio of the difference of maximum luminance and minimum luminance to the sum of max and min luminance • Contrast /modulation = L max – L min L max + L min • E.g. White stimulus in white background, contrast= 0% • Black in white background = 100 % • Expressed in percentage Luminance - The intensity of light per unit area of its source
    • 3. Contrast threshold • Object with the lowest contrast that a patient can recognize • The minimum contrast required to be able to see a target. • Contrast sensitivity : reciprocal of contrast threshold • CS = 1 / CT • Increase in CT = Decrease in CS • An object with the lowest contrast that a patient can recognize. • Expressed as percentage. • CS= reciprocal of CT • Maximum CT = 100% • CT depends on size of object
    • 4. Contrast sensitivity Ability to perceive slight change in luminance between regions which are not separated by definite borders. Photopic system is more sensitivity to contrast than the scotopic system • Snellen VA measures patients high frequency cut-off. • Normal high frequency cut off = 60 cycles/degree. • Snellen letter - not represent visual function in reality. • Refractive errors – decrease visual performance at mid & high SF. Contrast in VA letters
    • 5. Contrast Sensitivity •CS measurement for •To detect abnormal visual performance •To diagnose ocular disease & monitor its states •To predict performance on specific visual tasks •VA normal but CS of low & medium SF decrease in •Amblyopia, astigmatic error, cataract, diabetes, glaucoma, keratoconus, multiple sclerosis, ocular hypertension, optic neuritis & papilledema.
    • 6. Why to measure CS?
    • 7. Contrast Sensitivity Function (CSF) • Identical Snellen acuities can yield substantially different visual capabilities • Predicts the outcome of ophthalmic aids. e.g. the final reading speed with a magnifying device (Leat & Woodhouse) • Monitors the course of ocular disorders that result in contrast sensitivity reduction, such as cataracts or ARM • Monitors a variety of conditions that result in visual impairment • E.g. Multiple sclerosis - Snellen acuity within normal range, hidden losses in the mid and low spatial frequency domains (Pace & Woo, 1984)
    • 8. Example
    • 9. Contrast sensitivity of the human eye Modulation transfer function for a human eye at various pupil diameters. Curves for 2.0 and 2.8mm pupils cross over at about 27c/d.
    • 10. Contrast sensitivity Charts Pelli-Robson Chart Regan Low Contrast Chart Bailey Lovie Low Contrast Chart (10%) University of Waterloo Low Contrast Chart Cambridge Gratings Vistech Chart Lea Low contrast Chart Melbourne Edge Test Hieding Hiedi
    • 11. Pelli-Robson chart Score 2.0 = normal Score < 1.5 = visual impairment Score < 1 = visual disability
    • 12. Bailey-Lovie 10% low contrast chart100% contrast chart
    • 13. LEA low contrast chart
    • 14. Vistech chart • 6 rows • 3 inch diameter sine wave gratings • Each row a sample grating and a • series of test grating fixed spatial • frequency but varying contrast. • S.F 1, 2,4,8,16,24 c/d • Vertical ,slanted 15 deg to R, 15 deg to L
    • 15. Melbourne edge test •Use of boundary between light and dark background •20 circular stimuli each 2.5mm in diameter •Subject shown a key card vertically, horizontally and obliquely oriented
    • 16. Hiding heidi < 5% contrast cannot recognize face
    • 17. Cambridge low-contrast gratings Square wave gratings Spatial frequency: 4 c/d Varying contrast • Vector vision CSV-1000
    • 18. Addressing Reduced contrast Needs adequate magnification felt-tipped pens good lighting on object or print bold lined paper writing guide
    • 19. Types of contrast sensitivity loss Type 1 CS loss at high frequency Normal at low frequency E.g. early cataract, ARMD Type 2  CS loss at all spatial frequency Type 3  High frequency CS normal  Reduced CS at low frequency e.g. optic neuritis multiple sclerosis, POAG, Papilledema, Diabetes (Leguire and Regan 1991)
    • 20. Clinical Significance CS measurement for……….. • To detect abnormal visual performance • To predict performance on specific visual task driving ability good/ disable reading capacity mobility face recognition sports etc. • Contrast provides critical information about Edges borders and variations in brightness
    • 21. VA normal but CS of low & medium SF decrease o Amblyopia o Astigmatic error o Cataract o Diabetes o Glaucoma o Keratoconus o Multiple sclerosis o Ocular hypertension o optic neuritis o Papilloedema o Contact lens wearing Patient
    • 22. Factors Affecting CS •Age •Refractive Error •Lenticular Opacities •Pupil Size •Ocular Diseases •Systemic Diseases To diagnose ocular disease & monitorTo diagnose ocular disease & monitor its statesits states • Predicts the outcome of ophthalmic aids. e.g. the final reading speed with a magnifying device (Leat & Woodhouse) • Monitors the course of ocular disorders that result in contrast sensitivity reduction - cataracts - ARMD - RP
    • 23. Ocular Diseases Glaucoma  Advanced diabetic retinopathy Multiple sclerosis Media opacities Neurological problem Cataract Retinal disease Optic nerve disease Retrobulbar neuritis Corneal edema Multiple Sclerosis- DM Pituitary Adenoma Systemic diseases
    • 24. Addressing Reduced contrast
    • 25. Cont.
    • 26. CCTV Adjustable illumination, contrast & magnification system
    • 27. Glare • Refers to the presence of one or more areas in the field of vision that are of sufficient brightness to cause discomfort in vision. • Visual perception created by external light • Glare source : Axial / Peripheral • Reduces the quality of the image • an unpleasant sensation • a temporary blurring of vision • a feeling of ocular fatigue Classification • Veiling or disability glare • Discomfort glare • Specular reflection glare
    • 28. Veiling or disability glare Arises from stray light falling on the retina, usually from scatter by the media of the eye. Scattered light falls as a patch of veiling illuminance on the fovea and reduces the contrast of the retinal image. Reduces the contrast of the retinal image. Reduces visibility and visual performance. E.g. sky, sand, brightly illuminated walls etc.- the reflected images are large in angular sub tense leading to reduction in contrast observed in the visual field.
    • 29. Glare in Cataract Normal Cataract
    • 30. Discomfort glare Occurs when the illumination in a part of the visual field is much greater than the level of illumination for which the retina is adapted. Occurs when the ratio between the highest level of illumination in the visual field and background illumination exceeds a ratio of 3 to 1. An extreme case of glare often occurs during night driving- causes extreme discomfort.
    • 31. Specular reflection glare Occurs when patches of bright light are reflected form smooth, shiny surface into the eye. Typical reflecting surfaces include expanses of water, snowfields, roadways etc. Reflections are not only annoying but interfere with visibility, at times seriously. Can be well controlled by using polaroid glasses.
    • 32. Glare testing • Objective : • quantify the deleterious effects of light scatter on visual performance • Reduce the effect on impairment of vision • When? • Corneal opacities • Corneal dystrophies/ Degeneration • Cataract
    • 33. Pre& post-operative indications for glare testing Pre-operative Post-operative Cornea Cornea • Infectious scarring -PK • Traumatic scarring -Epikeratophakia • Degenerative scarring -Keratomileusis • Dystrophic scarring -Repaired laceration Lens Lens • Age-related cataract -PCO following ECCE,IOL • Traumatic cataract • Drug-induced cataract • Disease-induced cataract
    • 34. Glare Testers • Instrumentation • A glare source when introduced in an eye with media opacity causes some degree of visual disability. • Current glare testing devices gives this extent of disability in the form of reduced contrast sensitivity or visual acuity. • Brightness Acuity Tester (BAT) • Optec 1500 Glare Tester • Miller-Nadler Glare Tester • Terry Vision Analyzer (TVA)
    • 35. Assessment of Glare Brightness Acuity Tester Miller-Nadler Glare Tester
    • 36. Photostress test
    • 37. References • Clinical procedure of Primary Eye Care • Clinical Procedure of Optometry • Internet