According to the International Statistical Classification of Diseases and Related Health (ICD-10), there are 59 major types of diseases. Conventionally, these diseases can be divided into categories according to the degree of visual acuity, time of occurrence or cause disease. Let us examine closely.
Based on visual acuity ophthalmologists distinguished:
- Blindness. The complete absence of visual sensations or residual vision. When using the lens reaches the maximum visual acuity 0.04 diopters, or just the ability to light perception;
- Absolute blindness. Visual acuity is from 0.005 to 0.04 diopters;
- Visually impaired blindness. Eyes, in principle, operate informative function, but with a visual acuity of 0.2 diopters.
By the time of the appearance of pathology distinguished:
- Born blind. These are people who were born with the disease of view or get it up to 3 years of age;
- Blinded. People who have developed a defect, since the age of 3.
For reasons of illness share:
- Refraction disorder. The subject can not be focused clearly in front of the retina. There are two types of such disorders: ametropia (myopia or hyperopia) and astigmatism;
- Disorder of accommodation. The inability of a person clearly see objects at different distances. Known violations: accommodative asthenopia, spasm of accommodation, paralysis and paresis of accommodation;
- Disorder of peripheral vision. Inability to clearly see objects in motion or are on the sides of the test (hemianopia, scotoma);
- Disorder of adaptive capacity. Vision deteriorates when lighting conditions change (gimeralopiya).