Effect of Grouping on Lightness
Week 3: Contrast Sensitivity and Color Perception in Low Vision
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Refractive errors
Impact of reduced contrast sensitivity in low vision
Color-vision deficits in low vision
Cataract, U.S. and Nepal
Achromatopsia
ViaOpta Simulator
https://apps.apple.com/us/app/viaopta-simulator/id778653985
ViaOpta Simulator is a vision simulator app for the iPad and iPhone designed to help health care professionals educate patients about visual impairment due to the following eye diseases:
•Wet age-related macular degeneration
•Dry age-related macular degeneration
•Myopic choroidal neovascularization
•Diabetic retinopathy
•Diabetic macular edema
•Central retinal vein occlusion
•Branch retinal vein occlusion
•Vitreomacular traction/macular hole
Types of Refractive Errors
Myopia (nearsightedness/ short-sighted)
Difficulty seeing far away
Hyperopia (farsightedness/ long-sighted)
Difficulty seeing close up
Astigmatism
Blur due to an irregularly shaped cornea
Presbyopia (> 40 years old)
Difficulty seeing close up (for near objects)
Myopia (short-sighted)
Hyperopia (long-sighted)
Astigmatism
Presbyopia
Effective Contrast
Examples of Contrast Magnitude and Contrast Polarity
Definition of
Definition of CM:
CM = (Lmax – Lmin) / (Lmax + Lmin)
Michelson contrast ranges from 0 to 1.0
Demo of Pelli-Robson chart
Pelli- Sensitivity Chart
Contrast, Contrast Threshold, and Contrast Sensitivity
Contrast refers to a visual feature (especially light intensity) that distinguishes an object from its background.
Michelson contrast ranges from 0 (no difference in light intensity between an object and its background to 1.0 (maximum black on white or white on black), and is sometimes expressed as a percentage from 0 to 100%.
A Person’s contrast threshold refers to the lowest contrast they can see, such as the letters with lowest contrast visible on the Pelli-Robson chart.
A person’s contrast sensitivity is the reciprocal of their contrast threshold:
Contrast Sensitivity = 1 / Contrast Threshold.
A person with high contrast sensitivity can see very low contrast; they have a low contrast threshold.
Normal vision
Cataract removal by Phacoemul-sification
Artificial lens implant
Small Incision
Vision with cataract
Contrast reduction and Glare
Impediment to vision
S, M and L Cones
Butchart Gardens
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