Contrast sensitivity test is an assessment of the patient’s capacity to distinguish between light and dark. CS is the ability to identify subtle differences in patterns and shading or distinguish between similar shades. It is a critical measure of visual function, particularly in conditions of glare, low light, or fog when the contrast between objects and their background is often low.
CS is vital in detecting objects without distinct outlines and distinguishing objects or details from their background. A person needs good contrast sensitivity to detect fine features on people’s faces, to distinguish unmarked curbs and steps, or to see a gray car on a cloudy day.
Low contrast sensitivity may cause the loss of spatial awareness and heighten the risk of accidents. People with low contrast sensitivity can become a danger to themselves and others. Common symptoms of low contrast sensitivity include:
- Difficulty walking down steps
- Problems driving at night or in the rain
- Challenge pouring coffee into a dark mug
- Difficulty seeing people walking in dark streets
- Easier eye fatigue when watching television or reading
Low contrast sensitivity is not an indication of weakening or poor visual acuity. A patient may have 20/20 vision and also experience ocular and neurological disorders, which reduce their capacity to distinguish between an object and its background. Changes in CS can also occur due to aging or after refractive surgery, such as laser vision correction (LASIK) surgery or photorefractive keratectomy (PRK) surgery.
Also Known As
- Lea test
- Melbourne edge test
- Sine-wave grating test
- Pelli-Robson letter chart
- Functional acuity contrast test
- Mars letter contrast sensitivity test
- Hamilton-Veale contrast sensitivity test
Contrast sensitivity tests can be conducted at the eye clinic, hospital, or doctor’s office by:
- An optometrist
- An ophthalmologist
Contrast sensitivity tests are not routine eye exams. The doctor will order the test in exceptional cases to investigate specific complaints or concerns. Low contrast sensitivity is often associated with age, but may also be a symptom of severe health conditions. The doctor can use the contrast sensitivity test to check for a broad range of disorders, including:
- Retinitis pigmentosa
- Retinal detachment
- Diabetic retinopathy
- Optic nerve degeneration
- Age-related macular degeneration (AMD)
The doctor may also use the test for other medical reasons such as evaluating vision after contact lens fitting, sports vision testing and assessing the results of LASIK or cataract surgery.
Preparation & Expectation
The test is conducted after the standard acuity test to check vision. Patients who wear glasses or contact lenses can use them during the test. For patients with an eye disorder, the doctor tests each eye individually.
CS is an assessment of the capacity of the visual system to differentiate objects from the background. Usually, tests involve the presentation of digits or letters that are designed to become similar in brightness to the background until they are no longer visible. Gratings of parallel bars with different spatial frequencies can also be used.
Pelli Robson contrast sensitivity chart is the most commonly used device to test contrast sensitivity. It is the gold standard of contrast sensitivity measurement. It allows a quick, simple and accurate assessment of low spatial frequency CS when the test is done at the standard one meter. The chart consists of different capital letters arranged in parallel lines. The contrast reduces with each line. The patient moves down the chart to check the least level of contrast they can see.
The patient will sit or stand in a well lit room. The doctor will place the chart one meter in front of the patient with the center of the table at eye level. The doctor will block one of the patient’s eyes and instruct them to read the lowest letters they can see. S/he may encourage the patient to guess.
When the patient cannot see further, the doctor will point to the next lower contrast line on the chart and instruct the patient to look at the point for at least 20 seconds. Usually, with enough time at least an additional line of letter becomes visible.
The doctor will repeat the test in the other eye and can also conduct binocular measurement if necessary.
The doctor may also use other more sophisticated tests such as sine-wave gratings to assess the patient’s contrast sensitivity.
Results from the test will establish if the patient’s level of contrast sensitivity is caused by a refractive error or a problem that can be corrected with special glasses. The doctor may suggest or prescribe corrective lenses with a yellow filter because they better support the patient’s ability to notice differences in contrast. S/he may also recommend anti-reflective coating for the glasses. Many patients experience a better sight in low-light conditions when using lenses with an anti-reflective coating.
In severe cases the doctor may recommend surgery.
Risks & Complications
Contrast sensitivity tests are noncontact and non-invasive eye exams that have no risks or complications.