Eye structure and functions
We don't see by eyes, we see through them. They transfer information through optic nerve, chiasm and visual tract to certain areas of the brain end lobe where the image of the outer world is formed which we see. All these organs are parts of our visual analyzer or the visual system. The two eyes make our vision stereoscopic (form 3D images).
The right side of retina of each eye transfers through the optic nerve the “right part” of the image to the right side of the brain, the left retinal side operates in the similar mode. Then the two parts of the image are merged by the brain creating the final image. Since each eye receives “own” picture, when conjoint movements of the right and the left eye is disturbed the binocular vision can be disturbed as well. In other words you will have double vision or you will see two different pictures simultaneously.
Basic eye function
optic system projecting an image;
system that perceives and “encodes” the received information for the brain;
life supporting “servicing” system.
The human eye is a complex optic instrument. Its main goal is to “transfer” the correct image to the optic nerve.
Cornea is a transparent coat covering the front part of the eye. It has no blood vessels, but its refraction is great. It is part of the eye optic. Cornea borders sclera which is a non-transparent eye coat. See cornea structure.
Anterior chamber is a space between cornea and iris. It is filled with intra-ocular fluid.
Iris looks like a circle with an opening in the middle (pupil). Iris consist of muscles that change pupil size by constricting and relaxing. IT is a part of the eye choroid. Iris is responsible for the colour of the eyes (if it is blue this means it contains few pigment cell, if brown – a lot). Its function is same as of aperture in a camera – to adjust light flow.
Pupil is an aperture in iris. Its size usually depends on the illumination level. The more light the smaller the pupil.
Crystalline lens is the eye “natural lens'. It is transparent, elastic – can change its shape, focusing in almost instantly, therefore one can see well both near and far. It is located in a capsule and is withheld by ciliary zonule. The crystalline lens like cornea is a part of the eye optic.
Vitreous body is a gel-like transparent substance located in the posterior part of the eye. The vitreous body supports the sphere of the eye ball and is part of the intraocular metabolism. It is a part of the optic system.
Retina consists of photoreceptors (light sencing) and nerve (ganglion) cells. There are two types of receptor (transducer) cells in retina: cones and rods. These cells producing rhodopsin enzyme transform light energy (photons) into electric energy of neural tissue, i.e. photochemical reaction takes place.
Rods have high light sensitivity and allow seeing in poor light, they are also responsible for periphery vision. Cones adversely need plenty of light for functioning but allow to distinguish small details (responsible for direct vision) and ensure colour appreciation. Most cones are located in macula which is responsible for the sharpest vision. Retina adjoins choroid but not too snug in some areas. It is here that it may detach under various retina diseases.
Sclera is the non-transparent outer coat of the eye bulb and in the frontal part of the eye it verges into the transparent cornea. 6 eye moving muscles are attached to it. It contains a few nerve terminals and vessels.
Choroid inlays the back part of sclera, it adjoins retina and is closely linked to it. Choroid is responsible for blood supply of intraocular structures. And with retina disorders it is usually involved in the pathology process. Choroid has no nerve terminals therefore when there is a trouble there, there is no pain which usually alarms about a problem.
Optic nerve – transfers signals from nerve terminals to the brain.
Next: corneal structure
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