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What visually impaired people perceive

Looking, seeing, perceiving: three functions of vision, automatically integrated by sighted people. But these three sub-senses can be altered differently depending on the disease. Indeed, whether they are of embryonic, genetic, metabolic, parasitic, tumoral or age-related origin, all eye diseases do not affect the eye in the same way, and their consequences on the autonomy of sufferers can be opposite. Some diseases alter the peripheral visual field, affecting the perception of the environment but leaving the ability to look intact. Others, on the contrary, affect the central visual field, but have little deleterious impact on the peripheral visual field. Others degrade the entire visual field. Finally, some lead to total blindness with no light perception.

How does the eye work?

The lens in the eye allows light rays to be focused on the retina at the back of the eyeball. The retina transforms the light rays into signals sent to the brain by the optic nerve. The brain receives this signal and interprets it as the images we see. The slightest problem with any of these organs or processes can affect our vision.

The physical impacts of visual impairment

Depending on the disease and therefore on the type of impairment, the consequences on the autonomy and quality of life of the affected person will be very different. According to the different visual deficits, here is what they perceive:

Blurred vision:

The alteration of transparency plunges the person into a fog in which the contours of perceived objects are not very distinct. The vision of details is not very precise and colours are blurred. The person suffers from glare in the presence of light sources, although he or she needs the activity he or she is performing to be illuminated.

Central vision:

Central vision disorder is the most common type of visual impairment. This is where the visual impairment is in the central part of the retina. Shapes, colours, but especially the vision of details are affected. This makes it difficult to perform certain tasks, which can be important, such as reading, writing, precision work or recognising faces. On the other hand, the perception of space, large shapes and movements remains good. People with central vision impairment see more or less of a task, depending on the degree of impairment. These cases are often cases of AMD (Age-related Macular Degeneration) which mostly occur with age.

Peripheral vision:

In contrast to central vision, when peripheral vision is affected, it is the peripheral fields that are impaired. People can only see what they are looking at, like looking through a tube. They are still able to read, but the characters should preferably be small, so that they do not leave the field of vision. Also, they need more light to be able to see effectively. Movement is the main problem with this disability. It becomes difficult to maintain full independence. In this case, it is often glaucoma (associated with an increase in pressure inside the eye, which leads to an alteration of the visual field) or retinitis pigmentosa (progressive loss of peripheral vision) that are the causes of this disability.

Contrast sensitivity:

This is our ability to tell the difference between colours of a similar tone. For example, it is our ability to identify a white plate on a white tablecloth, or the features of a face. All eye impairments can lead to a decrease in contrast sensitivity.

Depth perception:

This is our ability to judge the distance to an object. Impairment in one eye can result in the loss of depth perception. This can make it difficult to grasp an object, or to perceive the height of a staircase.