Glaucoma is among the many factors that can cause changes in contrast sensitivity. Other conditions affecting contrast sensitivity include cataracts, age-related macular degeneration, myopia, optic neuritis, and retinal disorders.
When glaucoma affects your vision, it makes it harder for your brain to detect differences in luminance. In other words, glaucoma makes the contrast between an object and its background more challenging to detect.
What Is Contrast Sensitivity?
Contrast sensitivity is the eyes’ ability to identify an object not clearly defined from its background. Contrast refers to the difference in the luminance or colour that makes it possible to distinguish an object. It enables us to see well in different conditions, like foggy or rainy days, and allows us to identify road signs when driving during the night. Contrast sensitivity is vital to your visual function, especially in low-light situations.
Everyday situations that rely on contrast sensitivity include:
• Driving at night and in rainy or foggy conditions
• Reading materials with poor contrast, like a newspaper
• Navigating steps or curbs
• Locating an object against a similarly coloured background
• Distinguishing facial features of others
How Is Contrast Sensitivity Measured?
Contrast sensitivity isn’t measured in a routine eye exam but rather by using a Pelli-Robson contrast sensitivity chart, a Mars Letter contrast sensitivity test, or sine-wave grating targets.
• The Pelli-Robson chart features horizontal lines of uppercase letters in a uniform size. You start from the top of the chart and read each row until you can no longer see any letters against the white background.
• The Mars-Letter contrast sensitivity test features a similar chart, but the chart is smaller and viewed at a closer distance.
• Sine-wave gratings resemble fuzzy lines of alternating light and dark shades of gray. The thickness of the lines varies as you view them on a computer screen or a wall chart. It signals your doctor how well you can see under low, medium, and high-contrast situations.
How Does Contrast Sensitivity Differ From Visual Acuity?
Contrast sensitivity is sometimes confused with visual acuity, but they measure two different eye capabilities. Visual acuity refers to how sharp your vision is from a distance. Unlike contrast sensitivity, your visual acuity is tested during a routine eye exam.
Symptoms of Reduced Contrast Sensitivity
People with reduced contrast sensitivity may experience the following:
• Poor vision while driving at night and in rainy or foggy weather
• Difficulty gauging curbs and steps
• Eye strain from watching TV or reading
• Images that appear washed out
• Problems reading materials, like newspapers, where the print contrast against the paper background is poor
• Distinguishing objects that are similar in colour to their background, like finding a black wallet in a black purse; determining when your coffee is near the top when pouring it into a black mug, or picking out black socks in a shadowy drawer
• An inability to identify the food on your plate
If you experience any of the above symptoms, talk to your doctor and get tested for contrast sensitivity. The test is painless, requires no advanced preparation, and takes only a few minutes.
There is currently no cure for glaucoma. Therefore, it’s critical to be examined regularly by your doctor to detect glaucoma. The earlier glaucoma is detected, the more effectively your doctor can treat it. Glaucoma treatments can minimize or prevent vision loss and blindness in most cases.