the basic functions and the detailed definition of our eyes

5. The cornea is the part which allows light
to enter our eyes. The diameterof our eye
is approximately 2.3 cm in size. It is
cylindrical and dome shaped in shape.

7. Iris is the organ which regulates the amount of
light entering our eyes. It is coloured in black,
brown, red, green etc.
For eg: when we enter a dark room it takes
some time for us to see objects. This is because
there is no adequate amount of light entering
our eyes. And the illumination process is slow
and it takes some time for us to see objects in
dim room.

9. The pupil is the hole in the center of
the iris that light passes through.
When we focus and see an object the
pupil expands. Such as revertibly
when we do not focus an object the
pupil gets shrink. This also makes the
optic nerve to change its size.

11. This part helps to adjust the focal length of
our eyes according to our eyes. While
ageing this part loses the flexibility of it
and it arises as Presbyopia.

12. It is made of a transparent and
flexible material like a jelly made of
proteins.
It forms of a real image of the
objects on the retina of the eye

14. It is the ability of our eye lens to
adjust the focal length according to
the distance of the object from our
eyes. In ageing the power of
accomodation of our eyes decreases.
And the ciliary muscles loses the
flexibility.

15. The range of our eyes:
Our eyes can see objects ranging from (25
cm to infinity.)

16. The retina receives the light on it to
get a clear vision. It converts light rays
into electrical signals and sends them
to the brain through the optic nerve.
The retina is where most problems
leading to vision loss occur.

17. Each optic nerve has about 1.2
million nerve fibers. This is the
cable connecting the eye to the
brain. And it receives signals and
sends information to the brain.

19. The vitreous humour or vitreous humor is the
clear gel that fills the space between the lens and
the retina of the eyeball of humans and
other vertebrates. The vitreous is the transparent,
colourless, gelatinous mass that fills the space
between the lens of the eye and the retina lining
the back of the eye. It is produced by certain retinal
cells. It contains very few, no blood vessels, and 98-
99% of its volume is water with salts, sugars,
vitrosin, and a wide array of proteins in micro
amounts.

20. The aqueous humour is a clear, gelatinous
fluid similar to plasma, but containing low-
protein concentrations. It is secreted from
the ciliary epithelium, a structure
supporting the lens.It is located in, the
space between the lens and the cornea.

22. Myopia is a condition of the eye where the light
that comes in does not directly focus on the
retina but in front of it. This causes the image
that one sees when looking at a distant object to
be out of focus but in focus when looking at a
close object.
Myopia presents with blurry distance vision, but
generally gives good near vision. In high myopia,
even near vision is affected, and patients cannot
read without their glasses for distance.

25. Most nearsightedness is caused by a
natural change in the shape of the eyeball.
Other than the natural change in the shape
of the eyeball, there are a few rare causes
of nearsightedness. These are:
• Elongation of eye balls.
• Excessive curvature of eye balls.

26. • Pathological myopia, in which the back of the
eyeball continues to grow longer after
reaching normal adult size.
• Secondary myopia, which may develop as a
result of many conditions, including
premature birth and a number
of eye diseases.
• In some cases, nearsightedness may be caused
by eye problems such as cataracts,etc.

27. There is no universally accepted
method of preventing myopia.
Commonly attempted preventive
methods include wearing reading
glasses, eye drops and participating in
more outdoor activities. Concave lens
are used to treat this.

29. Hypermetropia, is a defect of vision caused
by an imperfection in the eye causing
difficulty focusing on near objects.
Farsightedness occurs when light entering
the eye through the lens is focused behind
the retina instead of directly on it.

32. Hypermetropia can be caused by
infections, injuries, migraines, aging or
genetics. This is caused by an eye that is
too short, whose cornea is not curved
enough, or whose lens sits farther back in
the eye than normal. Farsightedness is also
Inherited.

33. Minor amounts of hyperopia are
sometimes left uncorrected. However,
larger amounts may be corrected
with convex lenses in eyeglasses or contact
lenses. Convex lenses have a
positive dioptric value, which causes the
light to focus closer than its normal range.

35. Presbyopia is a condition where the eye exhibits
a progressively diminished ability to focus on
near objects with age. Presbyopia’s exact
mechanisms are not known with certainty; the
research evidence most strongly supports a loss
of elasticity of the crystalline lens, although
changes in the lens’s curvature from continual
growth and loss of power of the ciliary
muscles (the muscles that bend and straighten
the lens) have also been considered as its cause.

36. The first symptoms most people notice are
difficulty reading fine print, particularly in low
light conditions, eyestrain when reading for long
periods, blur at near or momentarily blurred
vision when transitioning between viewing
distances .These symptoms are usually first
noticed between the ages of 40 and 50.

38. Corrective lenses such as bi-focal lens can be
used to correct this defect. The upper part of
the glass is concave and the down part is
convex.