Contrast Sensitivity Test
Does glare from oncoming traffic make it extremely difficult for you to see? Do conditions of fog or snow make it almost impossible for you to see? Have you been diagnosed with a Cataract? You may need to have a Contrast Sensitivity Test.
What does a Contrast Sensitivity Test check?
A Contrast Sensitivity Test measures how low contrast situations such as glare, fog, rain, or snow conditions can affect your vision. Even though you may have 20/20 Vision in high contrast situations, your vision may be seriously decreased in low contrast situations.
See the simulation below of the same scene.
What are some reasons why your vision can be markedly decreased in low contrast situations?
Optical or Media (i.e., involving the transparent Cornea and/or Lens of your eye) conditions such as:
High Order Aberrations
Eye Problems or Neurological Problems such as:Early Glaucoma
Environmental or Personal Stressors such as:NightSmokeAltitudeWeather (fog, snow, rain)
As you can see, you may have 20/20 Vision in normal situations, but suffer from poor functional vision in low contrast situations resulting in loss of detail when driving at night, for example. Any of the conditions listed above can do this to your vision.
Why does a Sensitivity Test give you more information than a regular Eye Test Chart?
Eye Test Chart
consists of a number of high contrast, black-on-white letters, numbers, or figures of progressively smaller size. The smallest size that you can read denotes your visual acuity.
But in the real world, objects and their surroundings are of varying contrast.
Thus, the relationship between visual acuity and contrast allows a more detailed understanding of your real world visual perception and how that perception can change with time.
Contrast Sensitivity measures two variables, size and contrast while visual acuity measures only size. Contrast Sensitivity determines the lowest contrast level which you can detect for a given target size.
A range of target sizes are used to measure the lowest contrast level for each size and these findings can then be plotted on a graph.
What can you expect from a Contrast Sensitivity Test?
Examples of commercially available tests for Contrast Sensitivity:
Arden Contrast Sensitivity System: Consists of six photographic plates of gratings, with the first being a demonstration plate and the other five having varying spatial frequencies and contrast. Each grating is oriented vertically, with the contrast varying from the top to the bottom. For each plate, a card is moved downward over the page (the card masks the grating) until the point is reached at which the grating is seen. The examiner records the contrast from a scale provided with the grating.
Vistech VCTS 6500 Contrast Sensitivity System: Consists of three wall posters. Each chart contains five horizontal rows of nine circular sinusoidal grating patches oriented vertically or tilted 15 degrees to the right or to the left.Spatial frequency changes from row to row and the contrast level of each of the nine patches decreases progressively from left to right. You have to tell the examiner if you see the gratings and which direction are they going.
Contrast Sensitivity testing has many applications besides discovering optical/media disorders and/or eye diseases. For example, in the military, it can help to better predict real-world visual performance.
In order to standardize the illumination, and thus the contrast level, on these types of letter charts of varying contrast, the charts may have their own illuminator cabinets. See below:
Contrast Sensitivity testing can also help determine the visual function outcome of refractive surgery. If done before surgery, this testing can help communicate to you concerning your expectations for the quality of vision following surgery. In other words, if you already have low contrast difficulties before the procedure, then after surgery these may worsen.
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