The Eye and its structure
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In this article: · Introduction
of topic sentence. · Structure of
eyes. · Layers of
eyes. · Disorders of
eyes. · Related
posts. |
Hay! Guys, Our eyes are
being located in small portions of skull known as the orbits or eye sockets.
Eyelids wipe eye and prevent dehydration. They spread tears on eyes, which
contains substance for fighting against the bacterial infections.
Eyelashes prevent fine particles from entering
eye. The structure of eye can be dividing into three major layers.
The outer layer of eye
ball consists of sclera and cornea. Sclera gives eye, most of its white color.
It consists of dense connective tissues and protects the inner components of
eye and maintains its shape.
In front of, sclera forms the transplant
cornea. Cornea admits light to the interior of eye and bends light rays so that
they can be brought to a focus.
Layers of eye
The middle layer is
called choroid. It contains blood vessels and gives the inner eye a dark colour.
The dark colour prevents disrupted reflections with eye.
Behind cornea, choroid bends to form a muscular
ring called iris. There is a round hole, called pupil, in the centre of iris.
After striking the cornea, light passes through pupil. The size of pupils adjusted
by the muscles of iris. Pupil constricts in bright light when the circular
muscles of iris contrect.smilarly, pupil dilates in dim light when the redial muscles
of iris contract.
Behind the iris, there
is a convex lens, which focuses light on retina. Lens is attached to culinary
muscles of eye via a ring of suspensory ligament. To clearly see an object for
away, cilary muscles are relaxed and the lens become less convex. When cilary
muscles contracts, lens becomes more convex and round.
The inner layer is
sensory and is called as retina. It contains the photosensitive cell called the
rods and cones and associated neurons. Rods are sensitive to dim light and so distinguish
different colours.
Retina has two points. I.e. fovea and optic
disc. Fovea is a dip in retina, directly opposite to lens and is densely packed
with cone cells. It is largely responsible for colour vision and shapness.optic
disc is a point in retina where the optic nerves enter the retina.
There are no rods and
cones at this point that’s why it is also referred to as the blind spot.
The iris divides the
cavity of eye into two chambers. The anterior chamber is in front of iris i.e.
between cornea and iris; whereas the posterior chamber is between iris and
retina.
The anterior chamber
contains a clear fluid known as aqueous humor while the posterior chamber
contains a jelly –like fluid known as vitreous humor. It helps to maintain the
shape of eye and suspends the delicate lens.
Light from objects
enter eye and is refracted when it passes through cornea, aqueous humor, lens
and vitreous humour.lens also focus light on retina. As a result, the image
falls on retina.
Rods and cones generate nerve impulses in the
optic nerves. These impulses are carried to the brain, which makes the
sensation of vision.
Rods contain a pigment,
known as iodeosin. There are three main types of cones and each type has a
specific iodeosin. Each type of cones recognizes one of the three primary
colours i.e. blue, red and green.
If any type of cones is working well, it becomes
difficult to recognize the colour. Such person is also not able to distinguish
different colours. This disease is called colour blindness and it is a genetic
problem.
In human eyes there are
about 12.5 millions of rods and 0.7 millions of cones.
The presence of tappet
behind the eyes of cats and dogs make the eyes shiny when light refract from
their eyes the layer is capable for reflecting light from their eyes.
Too much light being
let in could damage the retina; too little light makes sight difficult.
Some of major eye
disorders are as follow
Disorders of the eye
1. Myopia (short sight).
2. Hypermetropia (long sight).
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