For normal vision, it is important that the light rays are well focused, that is, they fall exactly on the retina. This is achieved by changing the curvature of the lens. When we look at objects at close range, the lens becomes more convex. If we look into the distance, the lens reduces the curvature.
There are visual acuity disorders: hyperopia and myopia.
Myopia is the inability to clearly see distant objects. With myopia, the rays are focused in front of the retina. Myopia occurs when the eyeball is too long or the lens is too bulging.
To correct myopia, glasses with biconcave lenses are worn.
With farsightedness, a person sees well only distant objects, but indistinctly – close ones. Beams from closely spaced objects are focused behind the retina and a blurry image is formed on the retina. Farsightedness causes: a shortened eyeball or a flat lens.
Glasses with biconvex lenses are used to correct hyperopia.
Hygiene of vision
To preserve vision, you need to follow a few simple rules:
- when reading and writing, the light should fall from the left, there should be good lighting;
- cannot be read in moving vehicles;
- the distance from the eyes to the book should be 30–35 cm;
- after 30-40 minutes of reading, watching TV, working on a computer, you need to take a break;
- eyes should be protected from bright light;
- avoid injury to the eyes, foreign objects falling into them.
A good rest for the eyes is a regular stay in nature.