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Contrast sensitivity

Test per determinar la sensibilitat al contrast

Normally, when a person's vision is studied, he is looking at letters of a minimum size with a high contrast. In real life, we are normalley looking at objects that are not very small or with maximum contrast.

This fact can sometimes lead to people who complain about their vision and, on the other hand, when they have been examined, they have found a maximum visual acuity. Then it is convenient to study their contrast sensitivity, because if not, you can not explain why these complaints.

The images of the outside world are formed in the retina. The information is sent to the brain through many nervous fibers. Each of these nerve fibers specializes in a type of information. Thus, there are those that bring information about space frequencies, time frequencies, orientation, color, ... The image formed in the retina breaks down when sent to the brain and here the components are again joined. There are 4 to 6 channels of space frequency to detect the contrast.

One way to study contrast sensitivity is by presenting a test with a circle with vertical slopes of different inclinations to the right, on the top or left, with decreasing contrast until the patient is unable to distinguish the direction. This circle is presented at various frequencies and the following graph is obtained.

Franges inclinades per a estudiar el contrast
Resultat gràfic d´un estudi de sensibilitat al contrast

There are ocular pathologies that in the initial stages such as cataracts or age macular degeneration where there are losses at high frequencies. When the disease progresses affect the rest of the frequencies.

Optic neuritis, multiple sclerosis, open-angle primary glaucoma, visual lesions, diabetes, parkinson's, papiledema and Alzheimer's disease affect low spatial frequencies.

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