Light perception - the ability to perceive light in the range of solar radiation and adapt to the perception of visual images at different levels of illumination. The process of light perception begins in the rods and cones. Under the influence of the energy of light in rods and cones disintegrate special substance called visual purple. In the sticks of a substance - rhodopsin, which is formed from protein and vitamin A, and the cones - iodopsin, which included a iodine. Under the influence of light and rhodopsin ydopsin split, forming positive and negative ions and induce the appearance of the nerve impulse.
Color vision can take more than two thousand of shades of color depending on the wavelength of light. It is believed that the retina has three components that are configured on the perception of three primary colors of the spectrum: red, blue and green. Normal color perception is trihromaziya. In poor perception of one, two or three components arise tsvetoanomalii (protanopia, deuteranopia, acyanoblepsia).
Central and object vision - the ability to distinguish the size and shape of objects of the environment. Performed this function of the central fovea of the retina, where there are the best conditions for a function object vision. In the fovea contains only cones are densely packed and their processes form the optic nerve separate bundle called papilo-macular. Object vision depends on the ability to perceive the separate points. Each point is seen separately, if its image is projected onto each of two cones, between which is still at least one cone. That is, the size of the cones and determine visual acuity. It is believed that the minimum angle defined by the size of the cones is about 1 minute. Explore the visual acuity with all known tables Golovin-Sivceva.
Peripheral vision - the perception of space around a fixed point. When you commit a glance at some point, this point is seen the central fovea of the retina, and the space surrounding it is perceived by the rest of the retina. Space, which is perceived by one eye, called the field of view. Peripheral vision is important for orientation in the environment. For various diseases of the eye field of view may be narrowed, or fall out of certain areas (scotomata).
Stereoscopic vision - the ability to perceive the distance between the objects of the environment, the volume of these items, the ability to observe objects in motion. Stereoscopic vision is possible, if people perceive objects with both eyes - binocular vision. When violations of stereoscopic vision difficult orientation in the environment.
Normal visual acuity is provided by the optical apparatus of the eye. With the help of the optical media of the eye onto the retina is projected opposite the thumbnail of the object. For optical or refractive apparatus of the eye include:
They work as collecting lenses.
The refractive power of the optical apparatus of the eye is called refraction. She is 60 diopters (1 diopter - is the optical power of the lens with a focal distance of 1 meter, ie, collecting lens focuses the rays of 1dptr at a distance of 1 meter behind him.) In a normal refraction gives a projection image of an object on the retina. Clarity of images on the retina than the refracting apparatus of an eye depending on the size of the eyeball. This gives rise to various types of clinical refraction.
Emmetropia or commensurate refraction - a state of vision, when the focus of the optical system of the eye coincides with the retina.
Disproportionate refraction is called ametropia. By ametropia include:
If the focus of the optical system is the eye behind the retina, ie, a clear image is not formed on the retina, but behind the retina, a condition called a refractive error hypermetropia or hyperopia.
If the focus of the optical system in front of the eye retina and a clear image is formed before the rays reach the retina, such refraction is called myopia or nearsightedness.
In normal refractive errors in 60 diopters, parallel rays converge in the fovea of the retina. Parallel rays enter the eye from infinity. But at closer distances they change their course. It is believed that the parallel rays enter the eye from a distance of not more than 5 meters. If the object under consideration is less than 5 meters, then the image on the retina will be blurred. Then there is a need for a process of accommodation. The accommodation is due to increase refractive power lens.
The refractive ability of the lens increases with the transverse size of the lens. The lens is attached to the ciliary muscle, with a special circular tsinnovoy ligament. With the reduction of the ciliary muscle, which has the shape of a ring, the diameter of the ring decreases tsinnova ligament is weakened, diminished tension of the lens capsule and the lens becomes more convex shape, increasing its refractive power. In this eye sees better at short distances. The closer the distance, the greater the strain should ciliary muscle.
Simultaneously with accommodation are converging - the reduction of the visual axes of both eyes on one object. The nearest point of clear vision depends on the amount of accommodation. Accommodation volume depends on what size lens can increase its refractive power and is determined by the elasticity of the crystalline lens and ciliary muscle force.
With age, the elasticity of the lens is reduced - there is an age of change - presbyopia. In this case the eye is unable to adapt to the vision of close objects. It is believed that to 10 years in the lens can increase its refractive power of 14 diopters, and for fifty years has only 2 diopters. For the correction of presbyopia by wearing glasses is assigned to a collective lens. Points are selected in the office of an ophthalmologist.