Filters for pathologies
When one person's vision is studied, it is usually measured to what maximum visual acuity reaches. Doing it in this way is enough for most cases.
It can happen that the person presents a bad vision to a cause of a pathological origin. Then, it is advisable to investigate the contrast sensitivity. There are many diseases that are affected. This characteristic of the vision allows us to explain a lot of symptoms.
In any case, in real life, we are not looking at very small letters of high contrast or large letters with little contrast. The line of everyday activities is much more relevant to a person. This line is delimited by maximal visual acuity and maximal contrast sensitivity. In this area of the graph there is the majority of objects, which are neither very small nor very large, neither very nor little contrasted.
This line of activities of daily life, when there is an illness, moves down and to the left. People with little contrast and little vision have difficulties, for example, when they move because they do not distinguish the contours well, they do not differentiate well where a step of a stair begins and ends ...
The filters for pathologies do not improve visual acuity because there is an organic origin. What they do is improve the contrast because they reduce glare. For some pathologies, such as, for example, age macular degeneration, it can be greatly improved. The curve of daily life activities moves to the right.
There are other diseases (diabetic retinopathy, cataracts, retinitis pigmentosa, glaucoma, optic atrophy, albinism, optic neuritis, ...) in which it also improves the quality of life.