The outer layer of the eye consists of 8 eye parts.
1. Tear Layer
The Tear Layer is the first layer of the eye that light strikes. Its purpose is to keep the eye smooth and moist.
2. Cornea
The Cornea is the second structure that light strikes. It is the clear, transparent front part of the eye that covers the iris, pupil and anterior chamber and provides most of an eye’s optical power. It needs to be smooth, round, clear, and tough. It is like a protective window. The function of the cornea is to let light rays enter the eye and converge the light rays.
3. Anterior Chamber
The Anterior Chamber is filled with Aqueous Humor. Aqueous Humour is a clear, watery fluid that fills the space between the back surface of the cornea and the front surface of the vitreous, bathing the lens.The eye receives oxygen through the aqueous. Its function is to nourish the cornea, iris, and lens by carrying nutrients, it removes waste products excreted from the lens, and maintain intraocular pressure and thus maintains the shape of the eye. This gives the eye its shape. It must be clear to function properly.
4. Iris
The iris is pigmented tissue lying behind the cornea that gives color to the eye and controls the amount of light entering the eye by varying the size of the papillary opening. It functions like a camera. The color of the iris affects how much light gets in. The iris controls light constantly, adapts to lighting changes, and is responsible for near point reading (to see close, pupils must constrict)
5. Lens
The lens is the natural lens of the eye (chrystaline lens). Transparent, biconvex intraocular tissue that helps bring rays of light to focus on the retina (It bends light, but not as much as the cornea). Suspended by fine ligaments (zonules) attached between ciliary processes. It has to be clear, has to have a power of about +16, and has to be pliable so it can control refraction (This becomes less pliable as you age leading to presbiopia).
Ciliary Body. The circumferential tissue (a ring of tissue between the end of the choroids and the beginning of the iris) inside the eye composed of the ciliary muscle (involved in lens accommodation and control of intraocular pressure and thus the shape of the lens) and 70 ciliary processes that produce aqueous fluid.
6. Vitreous Humour (Chamber)
Vitreous Humour (Chamber) is the transparent, colorless gelatinous mass that fills rear two-thirds of the eyeball, between the lens and the retina. It has to be clear so light can pass through it and it has to be there or eye would collapse.
7. Retina
The retina is the light sensitive nerve tissue in the eye that converts images from the eye’s optical system into electrical impulses that are sent along the optic nerve to the brain, to interpret as vision. Forms a thin membranous lining of the rear two-thirds of the globe; consists of layers that include two types of cells: rods and cones. There is no retina over the optic nerve which causes a blind spot (This is the sightless area within the visual field of a normal eye. It is caused by absence of light sensitive photoreceptors where the optic nerve enters the eye.)
Cones The cones are the light-sensitive retinal receptor cell that provides the sharp visual acuity (detail vision) and color discrimination; most numerous in macular area. Function under bright lighting.Rods The light-sensitive, specialized retinal receptor cell that works at low light levels (night vision). The rods function with movement and provide light/dark contrast. It makes up peripheral vision.Macula It is the “yellow spot” in the small (3 °) central area of the retina surrounding the fovea. It is the area of acute central vision (used for reading and discriminating fine detail and color). Within this area is the largest concentration of conesFovea The fovea is the central pit in the macula that produces the sharpest vision. It contains a high concentration of cones within the macula and no retinal blood vessels.
8. Choroid
The vascular (major blood vessel), central layer of the eye lying between the retina and sclera. Its function is to provide nourishment to the outer layers of the retina through blood vessels. It is part of the uveal tract.
