4. Eyelid
Closes reflexively (blinks) to keep foreign
objects from entering the eye.
Blinking of the eyelid also cleans the
surface of the eyeball and keeps it moist
by distributing the moisture of the tear
glands over the surface of the eye.
5. Tears
Produced by lacrimal glands (
tear glands), which are located
under the upper eyelid on the
side away from the nose.
More than 90% water.
6. Another very important
component of tears is the
enzyme lysozyme, which
destroys bacteria.
LYSOZYME (lyse means
“to split”) breaks a
chemical bond in the cell
walls of bacteria, causing
8. Eye Structure 3 layers:
Sclera – outermost layer, often called the white of the
eye, and the transparent cornea.
Uvea – middle layer, includes the iris, the ciliary
body and the choroid.
Retina – innermost layer, is itself composed of 3
main layers of cells.
9. Iris
The part of uvea at the
front of the eye, which is a
continuation of the ciliary
body.
10. Pupil
In the center of the iris, the
opening through which lights
enter.
In bright light, the pupil becomes
small, in dim light, it becomes
large, allowing about 30 times
12. Function Of Retina
2 kinds of cells
1. Rods
- are long, thin cells with a diameter about 100th the
thickness of a human hair.
- receptors for night vision
2. Cones
-slightly shorter and thicker than the rods and have tips
shaped some-what like an ice-cream cone
-receptors for day vision and color
13. Fovea
-layer of nerve cells
Also slightly thinner , forming a
small depression on the retina.
The area that produces the
clearest vision
Contains much higher
14. The processed signals
are then relayed to the
visual centers of the
brain via the optic nerve.
At the point on the
retina where the optic
15. Transparent Interior
Aqueous humor
- a clear fluid which is produced from
blood circulating in the ciliary body.
Most important function is helping to
keep the eyeball reasonably firm and
in the proper shape.
21. 3. Astigmatism
optical defect in which vision is blurred
due to the inability of the optics of the eye
to focus a point object into a sharp focused
image on the retina.
due to an irregular or toric curvature of
the cornea or lens.
25. 6. Night blindness
Some people’s eyes do not
adjust to darkness,
remaining almost totally
blind in dimly lit places.
Usually caused by a lack of
26. 7. Glaucoma
A condition in which the pressure of the fluid
inside the eye becomes much higher than
normal, causing permanent damage to the cells
of the retina.
Common cause of blindness.
if detected in time, can be treated with drugs
or surgery to prevent the person from
