THE CONSTITUTION OF THE EYE
The eye is the organ which enables us to see while optical stimuli coming from the ocjects pass trough the corneal, lentical and vitreal layers of the eye and is transmitted to the brain via photoreceptors and nerves. Eyes remain settled in orbital holes near to each other on the head. This settlemend enables a depht perception. Eyelids enclose the eyes, protect the corneal layer from dryingand other outside influences via tear production. Ten-twenty winkings per minute keep the cornea wet and healthy. The eyelid margins are covered with sebaceous and aqueous glands responsible for tear production. Obstruction of these glands results in hordeolum formation. Lacrimal canals are placed at the upper and down endings of the eyelashes and obstruction of them ends in epiphora.
Six muscles covering the eye make the eye movements.
Sclera is the outer fibrous part of the eye protecting it from outside influences and keeps the eye spherical in shape.
Cornea is the transparent part in front of the eye. It has 75% of the refractive power of the eye, with the crystalline lens it enables a sharp image on the retina.
Choroid is a layer rich in blood vessels draining the ete. It is highly pigmented as well.
Ciliary Corpus is a tissue constituted of thin fibrils that keeps the crystalline lens, it plays a role in producing the aqueous humor and accomodation.
Iris has the eye color and crystalline lens is placed behind it is opening in the middle (pupil). It works as a diaphragm regulating the intensity of the ight entering the eye.
Crystalline lens is a thick elastic round tissue composed of protein fibrils. It is placed behind the iris and pupil. Its shape and therefore refractive power is changed via the muscles around itself.
Vitreus body is a gelatinous liquid covering the eyeball, it helps to maintain the spherical shape of the eye.It does not contain any vessels and nerves.
Retina is the nervous layer that consists rod and cone photoreceptors. These photoreceptors enables us dark and colored vision.Its thickness is 0.3mm.
It has a nervous layer consisting of the nerve axons and photoreceptor layer behind it. The axons constitute the optic nerve passinf through the lamina
Cone photoreceptors are the receptor cells sensing the motion, color and shapes of objects.
Rod photoreceptors are the receptor cells responsible for black&white and dark vision.
Fovea is the pit in the middle of the retina.Here is the visual acquity at a maximum level. Fovea has 145 000 cone photoreceptors.
Papilla: Fibers of the optic nerve unite, pass through the lamina cribrosa out of the eye. Here the fibers get myelinated. The part in the sclera is 1.5 mm thick and 1 mm long. It has a pale pink color and is oval in shape. The hole in the middle of the nerve is a place for arteries and venes of the eye.
Some information about the human eye:
-The diameter of an adult eye is 2.3 mm whereas it is 1.7 mm in a child.
-Tear production begins in the 3th week of the life, 84mg /hour is the production rate a child 38 mg/hour is the rate in adults.
-The optic nerve consists of 1 milion nerve fibers.
-The thickness of the sclera is beetween 0.3 and 1.35 mm.
-The thickness of the cornea is between 0.4 and 0.6 mm.