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Visual contrast sensitivity is the ability to distinguish between an object and the background behind it. Contrast sensitivity is different from visual acuity, which measures how clear your vision is at a given distance.
High spatial frequencies make up detailed features such as sharp edges, facial features, and similar. Low spatial frequencies are more like coarse images, where you can see the overall shape of something but not detailed features.
Visual acuity is measured when you read the eye chart during an exam. This is considered a high contrast test (black letters on a white background). You can have excellent visual acuity, but reduced contrast sensitivity and vice versa.
A contrast sensitivity test measures how well you can tell the difference between light and dark. For this, your doctor will use a different type of chart where the characters fade from black to gray gradually.
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Contrast sensitivity allows you to tell the difference between the foreground and background. It's an important aspect of your visual function, especially in low-light situations. Foggy conditions and situations with high glare require good contrast sensitivity for clear vision.
Common situations that require contrast sensitivity include:
Contrast sensitivity is essential to have in many low contrast situations. Patients with reduced contrast sensitivity may experience:
Contrast sensitivity is an essential measure of visual function. It is necessary to have good contrast sensitivity for safety when driving in low-vision conditions, such as rain, low light, glare, or fog. Numerous studies have shown that contrast sensitivity is a better predictor of driver visual performance than visual acuity.
Contrast sensitivity helps you see road signs, pedestrians, curves in the road, and the difference between the street and sidewalks. Having a contrast sensitivity deficit significantly increases your chance of getting in an accident.
According to a 2001 study, "Drivers with a history of crash involvement were 8 times more likely to have a serious contrast sensitivity deficit in the worse eye (defined as a Pelli-Robson score of 1.25 or less) than those who were crash-free...""Visual Risk Factors for Crash Involvement in Older Drivers With Cataract"
A routine eye exam does not include contrast sensitivity testing. If your eye doctor suspects you have a contrast sensitivity problem, the most common way to check for this is using a Pelli-Robson contrast sensitivity chart.
The chart features horizontal lines of uppercase letters in the same size. This type of vision test is usually performed while you are wearing your eyeglasses or contact lenses (if you need them).
As you go from left to right, the contrast of each letter will decrease. The patient starts from the top of the chart and reads each row until they can no longer see any letters against the white background.
The Mars Letter contrast sensitivity test uses a similar chart as the Pelli-Robson test, except that the chart is smaller and viewed at a closer distance.
A more sophisticated way of taking contrast sensitivity measurements uses sine-wave grating targets. Sine-wave gratings look like fuzzy lines of alternating light and dark shades of grey. Sometimes the lines are thicker, and sometimes they are thinner. The patient views multiple gratings on a computer screen or a wall chart.
This information tells the doctor how well you can see under low, medium, and high contrast situations. Your doctor can then plot a graph of these results, which is called contrast sensitivity function (CSF). CSF is more informative than visual acuity in determining an individual's spatial vision abilities.
A Snellen chart is different from a Pelli-Robson chart. Most ophthalmologists use the Snellen eye chart to measure visual acuity during an eye exam (visual acuity test). When you view the letter chart, you may notice that different letter sizes correspond to varying levels of visual acuity.
Then, they perform a refraction to see what your visual acuity is with your eyeglass prescription, which is your corrected visual acuity. Common refractive errors include astigmatism, myopia (nearsightedness), and hyperopia (farsightedness).
The lower the score, the poorer the contrast sensitivity.
Many factors contribute to loss of spatial contrast sensitivity, including some eye diseases.
These eye conditions include:
If you suffer from poor contrast sensitivity due to underlying eye disease, talk to your eye doctor about treatment options.
Potential treatments for certain eye conditions/diseases include:
Besides treating the underlying disease, wearing corrective lenses can improve contrast sensitivity. Schedule an eye exam to make sure you are wearing the correct eyeglass prescription, which helps with your overall vision.
Yellow-tinted lenses can help improve contrast sensitivity by increasing sharpness perception during the day. It is not recommended to wear yellow filter lenses while driving at night because they provide no additional benefits.
Also, ask your eye doctor to recommend the appropriate type of lenses. An anti-reflective coating reduces glare and helps you see better in dim conditions. Yellow or copper tinted lenses enhance contrast and work in low light environments.
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