What pigment deficiency affects the development of "night blindness"?

Hemeralopia is an ophthalmic pathology characterized by impaired adaptation of the visual analyzer in low light conditions. There is a popular name for hemeralopia - "night blindness", derived from the similarity of vision of chickens, which, due to the characteristics of the visual analyzer, do not see well in the dark and in low light conditions. Why do people develop hemeralopia? What structures of the retina are responsible for twilight vision? The main causes and mechanism of development of "night blindness", read on estet-portal.com.

What structures of the retina does the development of "night blindness" depend on?

The retina contains the receptor apparatus of the eye, which consists of light-sensitive cells. These cells include rod-shaped and cone-shaped cells. "Sticks" provide twilight and night black and white vision. "Cones" contribute to the perception of the color palette in the daytime. The ratio of rod-shaped to cone-shaped cells is normally 18:1. Therefore, vision at night and twilight depends precisely on rod-shaped light-sensitive cells, on their presence, as well as on their quality. The quality of rod-shaped cells is determined by the content of some pigment. Thus, the development of "night blindness" associated with rod cell function.

What pigment deficiency affects the development of "night blindness"?

The retinal rod cells contain the visual pigment rhodopsin. It provides dark adaptation of vision. The peculiarity of this pigment is that rhodopsin breaks down in the light, and in the dark with the participation of vitamin A it is restored. During the synthesis of the pigment rhodopsin, energy is formed, which is converted into electrical impulses and enters the brain through the optic nerve. Thanks to this mechanism, night vision and the normal activity of rod-shaped cells in general are ensured.

Changing the ratio of "cones" and "sticks", as well as a violation of the synthesis of rhodopsin contributes to the development of "night blindness". Its main manifestation is a decrease in visual acuity in low light, in daylight vision remains normal. There are 3 types of hemeralopia: symptomatic, congenital and essential.

For the development of "night blindness" triggers are needed, which are some states:

• past viral infections (measles, chickenpox, rubella, herpes);
• menopause in women;
• vegetarian diets.

The main causes of the development of "night blindness"

Symptomatic hemeralopia develops against the background of other pathologies of the visual analyzer. These are retinopathy, cataracts, high myopia, glaucoma, retinal detachment, chorioretinitis, siderosis, optic nerve atrophy and radiation burns of the eye. Congenital hemeralopia develops in the presence of genetic factors and is hereditary - family in nature. Hereditary "night blindness" common in Usher syndrome and hereditary retinitis pigmentosa.

Functional or essential hemeralopia develops in the presence of an acute deficiency or complete absence of vitamins PP, B2 and A in the body. Hypo- and beriberi develop with diabetes mellitus, liver pathologies, anemia, with severe exhaustion, with treatment with retinol antagonists (quinine), pathologies of the gastrointestinal tract, alcoholism and diseases that are accompanied by impaired absorption of nutrients.

From the moment of hypovitaminosis to the development of "night blindness"; it may take about 2 years, since the reserves of vitamin A in the body, when replenishment is stopped, last for a year. Different forms of hemeralopia develop according to the same mechanism – violation in the rod-shaped cells of the retina of the synthesis of the pigment rhodopsin.

About the symptoms and methods of treatment of "night blindness" read our next article.