Contrast sensitivity testing measures the eye's ability to distinguish an object from the background behind it. (CONTRAST SENSITIVITY)
In general, contrast sensitivity is affected by lighting, target size, motion, and shape.
This test is not done routinely like a visual acuity test, which checks the size of the letter that the eye can see, on a standard viewing plate and at a standard distance.
Despite this, this is A very important test and provides information about Quality of vision And on the capabilities of the visual system even more than the standard Snellen test.
A person can see 6/6 – this is the best vision in terms of sharpness but may have difficulty seeing when driving at night, or in twilight. In conditions of glare or fog, and when reading without good lighting due to low contrast sensitivity.
Signs of decreased contrast sensitivity
The first sign will be difficulty driving at night.
Difficulty identifying pedestrians walking in a dark area on the side of the road, rapid eye fatigue while watching television or reading a book, difficulty seeing stains on clothing and utensils, difficulty seeing a step or a step down from the sidewalk, which exposes the person suffering from this to the risk of falling.
Low contrast sensitivity when driving
Low contrast sensitivity – descending stairs
Low contrast sensitivity – in a ball game
How to test contrast sensitivity
As mentioned, this inspection is not done routinely, except when there are complaints indicating a specific problem.
The most common test is done using a tablet. PELLI-ROBSON and tests the patient's ability to distinguish letters when their size remains the same and the context gradually decreases. Each row has 6 letters whose contrast gradually decreases. The patient reads the letters until he or she is unable to recognize them. The test ends with a row in which the patient has read 2-3 digits/letters and no more. Using a computational formula, the result is given if the patient has decreased sensitivity to contrast.
Another test that is used is called FSC – CONTRAST SENSITIVITY FUNCTION (SIN-WAVE grating), This is a subjective test – which tests a patient’s ability to identify patterned stimuli of stripes with blurred borders at varying frequencies. The patient must report whether he sees the direction of the stripes. (Right, left, up) Here too, at the end of the process, the data is summed up in a graph that can provide information about the quality of vision and the ability of the visual system.
Factors affecting contrast sensitivity
- Refractive problem – uncorrected prescription for glasses
- Age and age-related diseases such as retinal degeneration
- cataract
- Contact lenses
- Refractive surgery – to lower the number
- Glaucoma
- Diabetic retinopathy
- Adrenal edema
- Drugs and toxic chemicals and more..
How to improve contrast sensitivity (CONTRAST SENSITIVITY )
If vision is impaired due to one of the above factors, the cause must be treated. For example, cataract surgery to replace the cloudy intraocular lens with a clear lens.
Sometimes the condition is irreversible, such as in glaucoma or retinal degeneration, and then it is necessary to use external factors to increase contrast.
Solutions:
Why a yellow color filter increases contrast?
The yellow filter And sometimes orange increases contrast and visual perception, increasing the ability to see the boundaries of an object better.
Use Anti-reflective lenses that reduce glare in night vision.
Use In lenses FREEFORM Which, using computerized solutions, creates a more precise lens for each area of the eye and prevents distortions by taking into account the angle between the eye and the back surface of the lens, changes in viewing directions, the size of the frame, and the position of the pupil in the frame.
