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# Contrast sensitivity testing
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A contrast sensitivity test measures your ability to distinguish between finer and finer increments of light versus dark (contrast).
This differs from common visual acuity testing in a routine , which measures your ability to recognize smaller and smaller letters on a standard .
Contrast sensitivity is a very important measure of visual function, especially in situations of low light, fog or glare, when the contrast between objects and their background often is reduced. Driving at night is an example of an activity that requires good contrast sensitivity for safety.
Even if you have , you can have eye or health conditions that may diminish your contrast sensitivity and make you feel that you are not seeing well.
## Symptoms of reduced contrast sensitivity
If you have low contrast sensitivity, you may have problems with night driving, including difficulty seeing pedestrians walking alongside poorly lit streets. Or you might notice that your eyes tire more easily while reading or watching television.
Poor contrast sensitivity also can increase your risk of a fall if you fail to see that you need to step down from a curb onto similarly colored pavement.
Low contrast sensitivity can be a symptom of certain eye conditions or diseases such as ,  or .
Changes in contrast sensitivity also can occur after , PRK and other types of refractive surgery.
For example, sometimes a person who has LASIK may be able to see 20/20 after the procedure but complains of poor night vision. This could be caused by a loss of contrast sensitivity from the surgery.
Conversely, some people achieve better contrast sensitivity and night vision after LASIK, compared with their vision with glasses or contact lenses before the procedure.
In most cases, people with cataracts notice a significant improvement in both visual acuity and contrast sensitivity after cataract surgery.
## Contrast sensitivity testing
Contrast sensitivity testing often isn't included in a routine eye exam. Your  might perform the test because of a specific visual complaint you have or because he or she suspects you have a condition that is affecting your ability to discern contrast.
Probably the most widely used device to test contrast sensitivity is the Pelli Robson contrast sensitivity chart.
Like a standard Snellen visual acuity chart, the Pelli Robson chart consists of horizontal lines of capital letters. But instead of the letters getting smaller on each successive line, it is the contrast of the
letters (relative to the chart background) that decreases with each line.
Other, more sophisticated devices also may be used to test your contrast sensitivity. These devices often use targets called sine-wave gratings that consist of a number of fuzzy, parallel bars of
light and dark. These bars can vary in width (spatial frequency) as well as contrast from target to target, to give a more thorough evaluation of how sensitive your eyes are to differences in contrast.
Some sine-wave grating tests include a bright light source that can be directed toward your eyes during the test to simulate glare situations such as oncoming headlights during night-driving.
If your eye doctor determines that you need a contrast sensitivity test, it likely will be administered after a standard visual acuity test and before your .
The testing typically is done while you wear your  or  if you require vision correction.
For evaluation of , contrast sensitivity usually is tested on each eye individually.
For other reasons, such as sports vision testing or to evaluate vision after contact lens fitting, LASIK or cataract surgery, the testing might be done with both eyes open.
## Contrast sensitivity function (CSF)
Detailed contrast sensitivity measurements that include both size (spatial frequency) and contrast are used to plot a person's contrast sensitivity function (CSF).
Sine-wave grating targets with thicker bars represent low spatial frequencies; targets with thinner bars represent higher spatial frequencies. In this regard, determining a person's CSF is much like evaluating the sensitivity of his or her hearing, which involves using tones of low and high pitch as well as variations in volume.
Your contrast sensitivity function essentially is a plotting of the curve that defines the lowest contrast level that you can detect for each spatial frequency tested.
Generally, objects with high spatial frequencies (sine-wave gratings with very thin bars) must have significantly higher contrast than objects with lower spatial frequencies (gratings with medium-width bars) to be detected by the human visual system.
## What can be done about poor contrast sensitivity?
Your contrast sensitivity test results can help your eye doctor determine if you have vision errors known as higher-order aberrations or some other problem that could be corrected with special eyewear or eye surgery.
If you are diagnosed with low contrast sensitivity, your eye doctor might advise you to wear corrective lenses with a yellow filter to improve your ability to discern contrast.
If you need prescription eyeglasses, many people find that they see better in low-light conditions when wearing lenses that include , compared with wearing the same prescription lenses without AR coating.
Also, eyeglasses with custom wavefront lenses sometimes can improve contrast sensitivity and night vision.
In some cases, custom or  can reduce higher-order aberrations and improve contrast sensitivity.
Certain premium intraocular lenses (IOLs) that have been designed with wavefront technology also can reduce higher-order aberrations and improve contrast sensitivity after cataract surgery.
Page published on Friday, January 3, 2020
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    - Color blind tests: Do you see colors as they really are?
# Color blind tests: Do you see colors as they really are?
A color blind test checks if you can accurately see colors.  If you cannot pass the test, you have a color vision deficiency — also calledcolor blindness.
Color blind tests can identify children who might have trouble recognizing colors. This could be a factor in certain activities in school and at home.
These tests can also identify people who might struggle at jobs that require perfect color vision.
There are two types of color blind tests:
1. Screening tests that can detect the presence of a color vision problem.
2. More in-depth tests that can detect a color vision deficiency *and* measure how severe it is.
## **Color blind screening tests**
A very popular test for color blindness is the Ishihara Color Vision Test.
Shinobu Ishihara, a Japanese ophthalmologist, developed the test more than 100 years ago. It can quickly detect red-green color blindness (the most common color vision deficiency).
Eye doctors use Ishihara plates to screen patients for color vision problems. Someone with a red-green color deficiency may not see the red number in this example.
The Farnsworth Munsell 100 Hue test identifies and quantifies color vision problems. (Image: Macular Pigment Research Group, Waterford Institute of Technology)
The Ishihara test consists of several circular images (or "plates"). Each image contains many dots of various colors, brightness and sizes.
A person who hasnormal color vision will be able to detect a visible number "hiding" within the array of dots.
But someone with red-green color blindness won't be able to see the number. Instead, they will see:
* A random pattern of dots, or
* A number different than the one seen by a person with normal color vision.
The complete Ishihara color blind test contains 38 plates. A shorter version of the test (with fewer plates) may be used during an  to screen for color blindness.
The screening takes place under normal room lighting. If you need , you will wear them for this test.
If you fail the Ishihara Color Vision Test, your eye doctor will talk to you about what this means for you.
## **In-depth color blind tests**
A screening test may be able to detect color blindness, but a more detailed color blind test is needed to measure how severe the condition is.
The most popular in-depth test is the Farnsworth-Munsell 100 Hue Test.
This test consists of four trays containing many small disks of varying hues. Each tray has a colored reference disk at one end.
You must arrange the disks in each tray to create a continuous sequence of color change.
This test should take place under room lighting that simulates natural daylight.
Each colored disk has a number on the bottom that enables the tester to compare the results against a key.
This comparison determines the type and severity of color blindness.
A shorter version of the Farnsworth-Munsell 100 Hue Test — called the D15 Test — contains 15 colored disks. Like the Ishihara test, the D15 test is for color blindness screening only.
## **Online color blind tests**
Many color blind tests are available online. Most of these tests are versions or variations of the Ishihara screening test.
Be aware that these online versions may be less accurate, based on the color accuracy of your display.
For the most accurate color vision testing, see your eye doctor.
## **Who should take a color blind test?**
Everyone should take a color blind test at least once in their lifetime, especially if their job depends on it.
Excellent color perception is required for certain technical and manufacturing positions. It's even more important for anyone considering a profession that requires *perfect* color vision. Examples include:
* Commercial artist
* Marketing professional
* Designer
* Electrician
Though there's no cure, people with color blindness lead full and rewarding lives. Specially tintedcolor blind glasses can help some people see colors more accurately.
#### Color blind tests: Do you see colors as they really are?