Contrast Sensitivity: Meaning, Testing, and Treatment 

Contrast sensitivity is your eyes’ ability to identify an object not clearly defined from its background. It enables us to see well in different conditions, such as foggy or rainy days, and allows you to identify road signs when driving during the night.

How Is Contrast Sensitivity Testing Useful?

Contrast sensitivity testing can supplement other tests during an eye examination. Doctors use the test to look for early symptoms of other ocular diseases, such as cataracts.

The test is also helpful in some jobs, such as flying an aircraft. It tests a pilot’s ability to identify small objects on the ground while airborne. You will need to take the test when applying for a driver’s license. 

Low contrast sensitivity makes it difficult to drive at night, even if you have normal 20/20 vision.

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Contrast Sensitivity vs. Visual Acuity

Contrast sensitivity and visual acuity are not the same thing. Visual acuity determines the sharpness and clarity of your vision from a distance. Contrast sensitivity refers to your ability to differentiate between an object and its background. 

Contrast sensitivity is also more sensitive than visual acuity, which makes monitoring it potentially more important. It can help doctors detect early signs and symptoms of some eye conditions. 

What Does Contrast Sensitivity Measure?

The contrast sensitivity test measures the overall function of your eyes in real-life conditions. It determines the least amount of contrast your eyes need to identify an object from its background. 

Symptoms of Reduced Contrast Sensitivity

If your contrast sensitivity is poor, you might experience these symptoms: 

• Difficulty driving at night
• Difficulty identifying steps on stairway.
• Eye strain while reading

Low contrast sensitivity can also be a symptom of some eye diseases like glaucoma.

What Affects Contrast Sensitivity?

Eye diseases are the most common reason for contrast sensitivity issues. But other factors can also affect contrast sensitivity, including:

• Age: Reduces contrast sensitivity because of the reduction in rods, which are eye structures responsible for vision in low-lit areas.
• Pupil Size: Affects the amount of light entering your eye. A small (mitotic) pupil will cause low contrast sensitivity by diffraction. Large (dilated) pupils cause low contrast sensitivity because of spherical abbreviations.
• Ambient light level: Increasing light in the room decreases contrast sensitivity as the extra light produces a counter effect to the lighting in the background.

Contrast Sensitivity Testing

Ophthalmologists can do contrast sensitivity testing, which they carry out when examining your eyes for any disorders. The test can detect any visual issues that are absent in a visual acuity test. The two types of contrast sensitivity tests are:

• Pella-Robinson test
• Sine-Wave Grating test

Pella-Robinson Test

This test measures contract sensitivity with the use of the Pella-Robinson chart. It has letters of different contrasts that gradually faint as you move down the chart. 

You will stand 1 meter away from the chart, cover one eye, and read from the top of the chart downwards. Continue reading till you can’t distinguish 2 or 3 letter in a row and repeat with the other eye. The doctors will base the results on how faint the letters you read were.

You can also do the computerized version of the Pelli-Robinson test at home without the help of a doctor. Unfortunately, the results are usually less accurate. 

Sine-Wave Grating Test

The sine-wave grating test is suitable for people who cannot read alphabetical letters, like infants. Because it is more refined than the Pelli-Robson test, it is ideal for clinical trials, but there are self-service vision booths. Doctors perform the test using a more subtle sine-wave chart. 

The chart does not have letters but rather alternating dark and white lines known as gratings, which vary in contrast and spatial frequency. Spatial frequency is the number of lines or bars per visual angle. 

Eye doctors will tell you to identify the gratings during the test. They will record the results depending on the contrast of the specified lines.

Understanding the Results of Contrast Sensitivity Testing

Contrast sensitivity scores are in the form of logarithmic values. If your contrast sensitivity is normal (100 percent), you will have a score of 2.0. It means that you can read at least two or three less contrasted letters perfectly.

If you have a visual impairment issue, your score will be 1.5, while those with visual disabilities have a contrast sensitivity score of 1.0. 

Treatment for Poor Contrast Sensitivity

You can improve contrast sensitivity by wearing yellow-filter glasses or by taking a medication called Brimonidine.

Yellow Filter Glasses

They are a special type of glasses that improve contrast sensitivity by reducing the light intensity entering the eye, therefore increasing the contrast of an object. They are especially helpful in foggy or misty conditions. 

Brimonidine Therapy

Brimonidine’s principal function is to relieve eye pressure. The drug can also improve contrast sensitivity that occurs after eye surgery by reducing the size of the pupil. 

FAQS

What is normal contrast sensitivity? 

A person with good vision will have an average contrast sensitivity score of 2.0. 

How do I check my contrast sensitivity? 

By using a Pelli-Robson test by reading letters on a chart. But if you cannot read alphabetical letters, you can use the sine-wave test. 

Why do yellow-tinted glasses help improve contrast sensitivity?

The yellow-tinted glasses reduce short-wavelength light. It thus increases the contrast of objects when you view them against a blue background.

References

1. The Contrast Sensitivity Function. (Retrieved February 2022). University of South Dakota Internet Psychology Laboratory.

2. Contrast sensitivity predicts pilots’ performance in aircraft simulators. (January 1982). National Library of Medicine.

3. Meeting the UK driving vision standards with reduced contrast sensitivity. (January 2016). National Library of Medicine.

4. Contrast sensitivity testing: a complete assessment of vision. (March 1989). National Library of Medicine.

5. Visual Acuity. (January 2022). American Academy of Ophthalmology. 

6. Visual acuity versus letter contrast sensitivity in early cataract. (June 1998). ScienceDirect

7. Factors Affecting Contrast Sensitivity in Healthy Individuals: A Pilot Study. (April 2017). National Center for Biotechnology Information.

8. The Effect of Test Distance on Visual Contrast Sensitivity Measured Using the Pelli-Robson Chart. (February 2021). National Center for Biotechnology Information.

9. How accurate is an LCD screen version of the Pelli-Robson test? (August 2018). National Library of Medicine.

10. Contrast Sensitivity. (Retrieved February 2022). American Academy of Ophthalmology.

11. Improvement of contrast sensitivity with yellow filter glasses. (April 1992). National Library of Medicine.

12. Brimonidine Ophthalmic. (July 2018). MedlinePlus.

13. Effect of brimonidine tartrate 0.15% on night-vision difficulty and contrast testing after refractive surgery. (September 2008). National Library of Medicine.