In order to explain what are the most common vision problems, it is essential to understand the anatomy and functions of the human eye and the visual system in general.
Broadly speaking, we can say that the visual system consists of: GLOBE EYE-WAY OPTICAL and Annexes.
The GLOBE consists of three layers and three cameras.
The layers are: sclerocornea, uvea and RETINA.
Cameras: The front, rear and vitreous.
The sclerocornea is the outermost layer and consists of SCLERA & CORNEA.
The sclera is the fibrous part that forms the "white of the eye", and has a protective function. In the outdoor area is covered by a mucous membrane called the conjunctiva transparent, which causes irritation to the familiar and frequent conjunctivitis. The very well known "nails" are also conjunctival problems.
The CORNEA is the transparent part of the outer layer is the "optical window" of the eye, and its function is, logically optics.
The uvea is the middle layer, and has three parts: the CHOROID, which is in the back, and is a function of both nutritious as pigmentary screen (to prevent light into the eye through which "should not"). The ciliary body in the middle, formed by the ciliary processes (responsible for the secretion of fluid that fills the anterior chamber and called AQUEOUS HUMOR) and the ciliary muscle, responsible for changing the curvature of the lens to focus at different distances. And the third part is the IRIS, which is in the anterior (the colored part of the eye) and whose function is to regulate the amount of light that enters the interior of the eye, which varies in size according to the light intnsidad.
Immediately behind the iris and ciliary muscles attached to is the CRYSTAL, the lens of the eye for excellence. Convex lens-shaped and is able to vary its curvature and hence its dioptric power by the action of the ciliary muscles. This is what allows to focus at different distances.
The RETINA is the area "sensible" of the visual apparatus. It's where you should form the images we see in order to "see" them clearly. Its front is blind, and sensitivity will increase as one moves away from the previous area. The point of maximum sensitivity is a small indentation called FOVEA, where there is a higher concentration of the cells responsible for the sensitivity of the retina: rods and cones. At the back is a blind part, where the optic nerve and connects called PAPILA.
The camera as part of the eyeball are three: the front, rear and VITREOUS.
PREVIOUS chamber is the area between the cornea and iris. Is filled with aqueous humor transparent liquid produced by the ciliary processes and is drained by the angle between iris and cornea. This drainage problems occur, of course, increased intraocular pressure and glaucoma resulting in the dreaded.
The camera BACK, also filled aqueous humor is the area between the iris and lens, and is where the ciliary processes.
The vitreous chamber is the area between the lens and retina, and is filled with a transparent gel called vitreous avascular.
The WAY OPTICAL constitute the transmission of nerve impulses from the retina to the cerebral cortex via the optic nerve. The receptor cells are those named rods and cones that convert the received images into nerve impulses that are transmitted to the brain via the nerve cited.
ANNEXES of the visual apparatus Loa are eye-MOTOR SYSTEM, consisting of six external muscles that cause mobility of the eyeball. The PROTECTION SYSTEM EFFECTS composed of ORBIT, LIDS, conjunctiva, TEAR, TEAR WAY AND TEAR GLANDS.
VISUAL ACT consists of 4 stages:
A normal eye, focused at infinity (from about 5 meters) is at rest. Apart from the possible contraction of the iris to control the amount of light (as in a camera with the diaphragm), the other part of the optical system dynamics, ie the lens is resting. In other words, that the human eye for distance does not need extra effort.
Logically, one eye focused at infinity, if something does not change its optical system, will blur a close distance, like if we focus a camera and photographed at a distance closer to another, the picture will be blurred.
And what varies is the thickness of the lens. When we need to focus at a close distance, the ciliary muscles into action and cause an increase in thickness of said lens, thereby increasing its power (the end of the day is a convex lens) and getting the right approach. This mechanism is called accommodation, and their decision is what causes presbyopia, which we commonly call "VISTA TIRED" and we see in another section of this website.