What is contrast sensitivity?
When someone is capable of seeing details at a large distance or reading very small letters, we say he or she has good sight. In ophthalmologic check-ups we are often asked to distinguish letters or symbols of decreasing size. This capacity is called visual acuity and it is the most common way of evaluating our visual system.
However, it is not the only way. Contrast sensitivity is the ability to distinguish shapes that have a luminosity similar to that of the background in which they are placed, that is, with little contrast. For example: the edge of a black step can be difficult to see if everything around it is also black, in a foggy day it is difficult to get your bearings because there are no contrasts, traffic regulations state that letters and numbers in license plates must be very dark with respect to the background (i.e. that they have high contrast) so that they are easily visible. In all those examples, the visual system must make use of the contrast, independently from stimuli size.
There are visual problems that especially affect contrast sensitivity, more than or sooner than visual acuity. This may happen in certain types of cataracts, optic nerve disorders or retinal disorders. For that reason, it is advisable to explore contrast sensitivity along with visual acuity in order to have a more accurate assessment of the visual function of a person.
Traditional methods to examine contrast sensitivity are not common at the ophthalmologist’s office. Some devices are expensive, and others gradually lose intensity and become useless after some time. Besides, they require the patients to have a certain degree of understanding and communication abilities. That is why very young children or patients with neurological disabilities are not able to use the most common contrast sensitivity tests.
DIVE includes a contrast sensitivity test that can be used with children from six months of age. Circles with black and white stripes appear on the screen and they gradually become gray, with progressively lower contrast, as the patient is able to detect them. When we see a striped pattern, we direct our sight towards the stimulus in a natural way, even the youngest children do it. Therefore, to perform the test the patient just needs to direct his gaze towards the circle with stripes, which he only look at if he is able to notice the difference in contrast.
The contrast sensitivity test in DIVE is an easy and fast mechanism that can be used in any type of patients, offering a more comprehensive assessment of the visual system.