The human eye is the most complex organ with which we receive and process information about the world around us. It consists of the eyeball, which has a spherical shape and auxiliary apparatus: eyelids, eyelashes, lacrimal glands and muscles.
The structure and structure of the eye
In order, we will analyze the structure and structure of the eye, consisting of three layers:
- Outer. The top layer is a thin transparent membrane (conjunctiva) that covers the inside of the eye and eyelids. The outer part of the eye is the cornea, which transmits and refracts light rays. The posterior part of the shell of the eye is an opaque sclera, which is penetrated by blood vessels. The organ is filled with intraocular fluid, which is under pressure, and the shell helps to maintain its shape, and also protects against mechanical damage. The anterior chamber of the eye is the space that is limited by the cornea and iris;
- Average. Under the fibrous layer is part of the choroid choroid , which saturates the tissues of the eyes with oxygen and ensures the outflow of fluid. Its front part is the iris, in the center of which is the pupil, the ciliary (ciliary) body, the lens. The iris, with the help of muscles, controls the pupil, letting in more or less light, depending on the conditions, like the diaphragm of a camera;
- Interior. Behind the vitreous body, which is filled with a gel-like fluid, is the retina. She is responsible for the perception of the image that enters through the cornea and lens. The retina consists of nerve cells and photoreceptors – cones and rods. Receptor cells distinguish color, light, convert this information into a nerve impulse. Then the optic nerve, like a wire, transmits this information to the brain.
How does the optical system of the eye work?
Cameras, telescopes, binoculars have lenses, just like the human eye. If you close your eyelid, and then gently run your finger over it, you will feel a bump – this is the cornea – the convex lens of our eye. In order for a person to see something, light is needed. The pupil is nothing but a hole. Through it, the light that emits or reflects objects enters the lens. It is a transparent biconcave lens and collects all the rays at one point and forms an exact inverted copy of the object we are looking at. In other words, the lens reduces the image and transmits it to the retina.
About 7 million cones, sensitive to red, blue and green, send signals along the optic nerve to the brain, and the visual analyzer converts them into colors. When it gets dark, the less sensitive cones become powerless. But we must see something. Rods are responsible for the perception of light, and there are many more of them: about 100 million. At dusk, the pupils dilate to let in the smallest rays of light and navigate in space without distinguishing colors. By the way, it is precisely because of genetic or acquired problems with cones that color blindness arises – the inability to correctly distinguish colors.
The rods are predominantly located along the periphery, and the cones are concentrated in the place of maximum visual acuity – in the center (in the region of the macula, or macula). Light information falling on this part of the retina is the most clear, bright and complete. Also, everyone has a blind spot on the retina. This is normal, it’s just that there are no photoreceptors in this place, because the optic nerve is attached to it.
Even in such a cunning and almost perfect system, something can fail. Fortunately, many visual impairments are reversible, and even the development of serious diseases can be slowed down or stopped if you consult an ophthalmologist in time. Even if there are no complaints, a routine eye examination should be done at least once a year.
The standard examination includes:
- Visometry – checking visual acuity according to the table;
- Computer refractometry to assess refractive errors;
- Perimetry – assessment of changes in peripheral vision;
- Ocular tonometry – measurement of intraocular pressure (IOP);
- Biomicroscopy on a slit lamp;
- Ophthalmoscopy – examination of the fundus of the eye.
What symptoms should not postpone a visit to the ophthalmologist?
- Decreased visual functions;
- Narrowing of the visual fields;
- The appearance of spots (cattle), veils or rainbow circles before the eyes;
- Pain and discomfort with eye movements;
- Problems with color perception and adaptation to changes in lighting;
- Frequently recurrent eye infections.