Structure, Functions And Diseases of The Human Eye

The human organ of sight is the eye which is spherical in shape and
structured with visual receptor such as the rods for bright light and
the cones for bright light. The eye is so important to human because
without the eyes we cannot see and when we cannot see we cannot enjoy
the essence of life.

The following structures make up the human eyes

The sclerotic layer
This is a thick and fibrous tissue forming the white eye. Therefore
the sclera is the ' white eye ' and it gives shape and fitness to the
eye as well as protecting and supporting the inner parts of the eye.

Cornea
It is that part of the sclerotic layer which burges out in front of
the eye. The cornea is transparent thus admits light into the eyes.
This it does by bending the light rays in order to bring them to a
focus on the retina.

Optic nerve
This is located at the back of the sclera. It helps in transmitting
sensory impulses to and from the brain.
Conjunctiva
It allows the passage of light into the eyes and protects the
innermost delicate parts of the eyes.
Iris
This serves as a measure device for the amount of light entering the
eyes. It helps to protect the eyes from damage as a result of too much
light entering the eyes.
Choroid
This is the brownish or reddish part of the eyes that house that black
pigment in the eyes. It is highly vascularised, pigmented and
providing oxygen and food to the cells of the eyes. It also absorbs
light rays and prevents reflection of light in the eyes through the
pigment .
Pupil
This is the opening through the iris. The light enters the eyes
through the pupil and it also control the amount of light entering the
eyes.
Lens
The lens is transparent in nature, elastic, held in position by the
ciliary muscle and is biconvex in shape. It makes fine adjustment of
focusing image on the retina through the refraction of light entering
the eyes.

Ciliary muscle
The ciliary muscle helps to hold the lens in place through the
suspensory ligaments attached to it. The cliary muscle changes the
focal length thus making proper accommodation of the eye to be
possible.

Retina
The retina is the innermost and sensitive part of the eyeball. Images
are formed on the retina. Light rays come to a focus on the retina.
Detection of color is possible through the retina and is so sensible
to light.
The retina have sensory cells such as the rods and the cones.
The most sensible part where image is fully formed and transferred
from the retina to the brain is the yellow spot. The blind spot as the
name implies is not sensitive to light. The optic nerves connect to
the brain through the blind spot.
The aqueous humour is a transparent and waxy liquid filling the space
between the lens and the cornea. While the vitreous humour is also a
transparent but jelly-like liquid filling the space between the lens
and the retina.

The two major function of the eye are image formation and accommodation.

Accommodation is the ability of the eye to focus both near and distant
object on the retina.
Image formation is possible by the passage of light through the
conjunctiva, cornea, aqueous humour, lens and the vitreous humour
finally to the retina. Though, the image is smaller and inverted on
the retina but all these will be corrected by the brain.

General care of the eye

Avoid irritating the eye with dust or smoke

Use clean cloth such as clean handkerchief to clean the eyes

Avoid habitual rubbing of your eyes with dirty finger

Read books under correct lighting conditions e.g avoid the use of
candle to read book

Don't clean your eyes with dirty water

Consult physician before taking any antibiotic eye drops

Consult a doctor in case you feel the symptoms of any of the following
eye defects

Major type of eye defects and their correction

1. Long-sightedness
Also called hypermetropia is an eye defect in which parallel light
rays from near objects are focus behind the retina instead of focusing
on the retina.
Correction
Wearing of convex or converging lenses.

2. Short-sightedness
Also called myopia is an eye defect whereby the parallel light rays
from a distant object are made to focus in front of the retina instead
of focusing on the retina.
Correction
Wearing spectacles made with concave or diverging lenses.

3. Presbyopia
This is a condition of losing the elasticity of the lens and the
ciliary muscles as a result of old age.

4. Astigmatism
This kind of eye defect is caused by unequal curvature of the cornea or lens.
Correction
Wearing of spectacle made of cylindrical lenses.

Conclusion
The eye is the light of the body. If your eye is clear, your whole
body will clear. Take proper care of your eye. Avoid play or job that
can cause premature defection of your eye. Don't be afraid or
reluctant to wear prescribed spectacle to improve or support your eye.
Avoid using over the counter medicine for the eye but consult a
qualified physician before using any eye drop or spectacle.

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