Download Functions of the eye parts

Functions of Eye Parts
Aqueous Humor -
Between the iris and the cornea is a space filled with a
watery fluid called the aqueous humor. This has a
refractive index of 1.336. The aqueous humor bathes both
the cornea and the lens.
Cornea -
The front portion of the sclera has a section that is
transparent. This transparent window known as the cornea
is attached to the sclera and is a major refractive power of
the eye. The refractive index is 1.376. The cornea acts as
the eye's outermost lens. It functions like a window that
controls and focuses the entry of light into the eye.
Iris -
The iris is a muscular and pigmented tissue forming a
circular curtain with a hole in the centre. The hole in the
centre of the iris is called the pupil. The iris controls the
amount of light which enters the eye by changing the pupil's
diameter.
Optic Nerve
The optic nerve connects the retina to the lateral geniculate
nucleus, which is in the middle of the brain. This is the first
connection made by the visual system in the brain.
Retina -
The retina is made up of transparent, sensory and nervous
tissue carrying blood vessels, nerve cells and nerve fibers. At
the back of the retina, the nerve fibers all come together
and emerge as the optic nerve.
The nerve endings on the inside of the wall of the retina
terminate in light-sensitive cells of two types, rods and
cones. Rods are used for peripheral vision and night vision.
Cones require bright light and provide fine detail and color
vision. The point on the retina where the nerve fibers leave
to form the optic nerve is called the optic disc or blind spot.
Sclera -
The outside covering of the eye is a protective envelope of
leathery connective tissue known as the sclera. This is the
white coating on the outside of the eyeball, commonly
known as the white of the eye. It completely envelops the
globe except at the front of the eye and maintains the shape
of the globe. It also provides a firm anchorage for the extra
ocular muscles that control the eye's movement.
Lens -
provides a clear medium through which light rays from an
object can reach the retina
focuses a sharp image of an object on the retina
varies its refractive power, thus providing clear images of
objects over a wide range of distances
flatter = longer focal length and vision for distance
rounder = shorter focal length and vision for close up
creates a functional barrier between the anterior
and posterior segments of the eye
the refractive index of the lens is 1.376 – 1.406
Tapetum -
A reflective layer under the retina which serves to intensify
vision in dim light. The "mirror" effect of the tapetum
results in the "eye shine" observed when an animal looks
into a car's headlights. While dim light vision is enhanced by
the tapetum, scattering of the reflected light may result in
reduced acuity.
Vitreous Humor -
A jelly-like transparent fluid fills the inner chamber of the
eye. This fluid is called the vitreous humor, and it is
contained in a thin membranous sac called the hyaloid
membrane. The fluid of the vitreous humor has a refractive
index of 1.337.
Note
For you to see clearly, light rays must be focused by the
cornea and lens to fall precisely on the retina. The retina
converts the light rays into impulses that are sent through
the optic nerve to the brain, which interprets them as
images.