POWERPOINT NOT MINE. CREDITS TO THE RIGHTFUL OWNER. I JUST SHARED IT HERE SO I CAN PUT A LINK TO MY BLOG. I'M TOO LAZY TO TYPE ALL THESE ONE BY ONE LOL

1. The Human Eye
With this presentation, we will tackle
about the following:
a. Parts of the Human Eye
b. Functions of the Parts
c. Defects of the Human Eye

2. Fundamental Parts of the Human
Eye

3. Functions of the Parts of the Human Eye
The human eye is the sense organ which helps us to see the
colorful world around us.
The human eye is like a camera. Its lens system forms an
image on a light sensitive screen called retina. The eye ball is
almost spherical in shape with a diameter of about 2.3cm. Light
enters the eye through a transparent membrane called cornea.
Behind the cornea is a muscular diaphragm called iris which
has an opening called pupil. The pupil controls the amount of
light entering the eye. The eye lens helps to focus the image of
objects on the retina. The ciliary muscles helps to change the
curvature of the lens and to change its focal length.

4. The macula allows us to appreciate detail and
perform tasks that require central vision such
reading. The vitreous humor comprises a large
portion of the eyeball. It is a clear gel that
occupies the space behind the lens and before
the retina at the back of the eye. Because the
eye must process visual data, this liquid must
be clear enough that light can easily pass
through. The optic nerve transmits electrical
impulses from the retina to the brain. It
connects to the back of the eye near the
macula.

5. Human Eye Defects
Myopia (Near Sightedness) is a defect of vision in which a person
can see nearby objects clearly but cannot see distant objects clearly
because the image is formed in front of the retina.
This may be due to :
i) Increase in curvature of the eye lens
ii) Increase in the length of the eye ball
It can be corrected by using suitable concave lens.
Myopic eye
Correction using concave lens

6. Hypermetropia (Far Sightedness) is a defect of vision in which a
person can see distant objects clearly but cannot see nearby objects clearly
because the image is formed behind the retina.
This may be due to:-
i) Decrease in curvature of eye lens
ii) Decrease in the length of the eye ball
It can be corrected by using a suitable convex lens.
Hypermetropic eye
Correction using convex lens

7. Presbyopia is a defect of vision in old people in which they
are not able to see nearby objects clearly due to the
increase in the distance of near point.
This is due to the weakening of the ciliary muscles and
decrease in the flexibility of the eye lens. It can be
corrected by using suitable convex lens.
Sometimes they are not able to see both nearby and
distant objects clearly. It can be corrected by using bifocal
lenses consisting of both concave and convex lenses. The
upper part is concave for correction of distant vision and
the lower part is convex for correction of near vision.

8. Astigmatism is a defect in the eye when the light rays do
not all come to a single focal point on the retina, instead
some focus on the retina and some focus in front of or
behind it. This is usually caused by a non-uniform
curvature of the cornea. A typical symptom of
astigmatism is if you are looking at a pattern of lines
placed at various angles and the lines running in one
direction appear sharp whilst those in other directions
appear blurred. Astigmatism can usually be corrected by
using a special spherical cylindrical lens; this is placed in
the out-of-focus axis.

9. A cataract is a clouding of the lens, which
prevents a clear, sharp image being
produced. A cataract forms because the lens
is sealed in a capsule and as old cells die
they get trapped in the capsule, with time
this causes a clouding over of the lens. This
clouding results in blurred images.

10. Age-related Macular Degeneration (ARMD)
is a degenerative condition of the macula
(the central retina). It is caused by the
hardening of the arteries that nourish the
retina. This deprives the retinal tissue of the
nutrients and oxygen that it needs to
function and causes a deterioration in
central vision.

11. Glaucoma is a disease caused by increased IOP
usually resulting from a malfunction in the eye’s
drainage system. The eye produces a clear fluid
(aqueous humor) that fills the space between the
cornea and the iris. This fluid filters out through a
complex drainage system. It is the balance between
the production and drainage of this fluid that
determines the eyes intraocular pressure (IOP).
Increased IOP can cause irreversible damage to the
optic nerve and retinal fibers and if left untreated can
result in a permanent loss of vision.