The human eye is a light-sensitive organ that has achieved a high degree of specialization, distinguishing many nuances such as colors, contrasts or different degrees of sharpness and blurriness. Today we will study the parts of the eye human.

human eye

How do we see?

El visual process It is both a sensory and motor process that allows us to interpret information from the world around us. In this process we can distinguish three stages.

The first consists of a physical stage in which the light that is reflected by an object enters our eye and once inside, go through the different transparent structures (cornea, aqueous humor, crystalline y vitreous humor) until you get to focus on the retina.

In the second stage, this light stimulus that has been received turns into nerve impulse and goes through the optic nerve to the occipital lobe of the brain.

In the third stage the nerve impulse is interpreted that had been received.

Parts of the eye

To achieve all this basic visual process, it is necessary that the anatomy of the eye and its complementary structures develop perfectly from childhood and there is no alteration that hinders the maturation process of the visual system.

The ocular anatomy is formed by different ocular structures:

Each of these structures is made up of different components, but we will only focus on those that may have more relevance when light enters the eye, either because they serve as a filter or because they are structures that are more sensitive to the effects of this light. For this reason, within the eyeball we will highlight four components:

  • The cornea
  • El iris
  • The lens
  • The retina

The cornea

The cornea is located at the front of the eye in front of the iris. It has an optical function (refracting the light that passes through it to be able to focus on the retina) and a protection function. On the front it is in contact with the tear film and borders the eyelids, while the posterior part is hydrated and nourished by the aqueous humor existing in the anterior chamber.

It is composed of five layers, of which we highlight the thickest layer, called corneal stroma and representing the 90% of the total corneal thickness, and the innermost layer, the endothelium, where there are cells with little capacity for regeneration but of great importance for the maintenance of this corneal structure. The regular arrangement of the fibrils, the cells of all the layers and the fact that it is an avascular structure allow it to be transparent.

parts of the eye

The cornea is the first natural filter of the eye, since it absorbs light with a wavelength approximately less than 295 nm, such as part of the ultraviolet radiation. 

the iris

The iris is located behind the cornea and is made up of pigment cells and muscle cells that delimit a central opening known as pupil.

The dilation of this pupil (mydriasis) or contraction (myosis) is achieved by the action of the iris dilator muscle and by the iris sphincter, thus controlling and regulating the amount of light entering the eye.

The lens

The lens is the second diopter or lens of the eye. It is a biconvex lens that is transparent, without vascularization or nerves. It is previously limited by the iris (without coming into contact with it) and subsequently with aqueous humor. By means of the Zinn zonula filaments that attach it to the ciliary muscle and thanks to the elasticity of the lens, we are able to focus at different distances. As the years go by, this structure loses elasticity and transparency, leading to presbyopia or senile cataracts.

The lens is also the eye's second natural filter, as it absorbs wavelengths between 320 and 400nm, protecting the retina from near ultraviolet radiation. It also partially protects the retina from blue light, although it is also necessary for proper visual function and other physiological cycles.

This filter does not have the same efficiency throughout life, since younger eyes have a higher transmittance for short wavelengths. With age, the number of chromophores in the lens increases, increasing its absorption power and, with this, also increasing the protection of the retina against ultraviolet radiation. On the contrary, the possibility of photochemical reactions in the lens due to the effect of this light, increases the probability of suffering Cataracts.

The retina

The retina It is located covering the innermost part of the eyeball and is responsible for receiving the light stimulus from the external environment, transforming it into a nerve impulse so that it is later transmitted to the occipital area of ​​the brain to be interpreted. It consists of 10 layers, among which we will highlight the layer of photoreceptors and the layer of pigmentary epithelium of the retina

There are two types of photoreceptors: cones and canes. The former are responsible for the finest discrimination and color. The sticks are more sensitive to the perception of light and therefore are the most used in scotopic conditions (night vision). When the light hits the photopigment of the photoreceptors, a chain of chemical reactions is initiated, which causes this luminous stimulus to transform into a nervous impulse in the pigmentary epithelium of the retina.

Among the functions of the retinal pigment epithelium we find the regeneration of photopigments and the phagocytosis or elimination of waste material. Some of this material can not be completely eliminated and accumulates in the form of lipofuscin in the retina. This accumulation of material increases as the years pass and can affect the functions of the pigment epithelium. This function of eliminating this material can be altered by light toxicity and chemical reactions of oxygen metabolism.

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Parts of the eye
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Parts of the eye
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We explain the parts of the eye in detail. If you want to know what the human eye is like, go here to find out. We are a specialist ophthalmology center.
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Área Oftalmológica Avanzada
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