human eye

2. THE EYE
• The eye is organ of sight which is situated in
the orbital cavity.
• It is supplied by the Optic Nerve (2nd cranial
nerve.
• Shape- spherical (2.5 cm in diameter)

3. STRUCTURE OF THE EYEBALL
1. Wall of eye ball.
2. Light transmitting media (or) refractive
media

6. WALL OF THE EYEBALL
1. Outer layer (fibrous coat) : Sclera and Cornea
2. Middle layer (vascular coat) : Choroid, Ciliary
body and Iris
3. Inner layer (nervous coat) : Retina

7. Sclera and Cornea
• Sclera or the “white of the eye” forms the
outermost layer of the eyeball
• The anterior one sixth part of the sclera is
transparent and is known as cornea. The
cornea is described as the “window of the
eye”
• Light rays pass through the cornea to reach the
retina.

8. Choroid
• Choroid is a thin pigmented membrane, dark
brown in color which is situated in between
sclera (externally) and retina (internally).

9. Ciliary Body
• Ciliary body is the continuation of choroid
consisting of smooth muscle fibers, i.e, cilliary
muscles.
• Ciliary body contains suspensory ligament for
attaching the lens in position.

10. Iris
• Iris is the pigmented membrane surrounds the
pupil
• It arises from the margin of ciliary body and
forms a dark centered opening called pupil.
• The space between cornea (in front) and the
lens (behind) is the anterior segment which is
filled with a clear fluid, the aqueous humor.

11. Retina
• Retina is the inner most layer of the eyeball.
• The outer surface of the retina, formed by
pigment cells, is attached to choroid.
• There are two types of photoreceptor cells in
the human eye rods and cones.

12. Cont..
• These cells contains photosensitive pigments
(Rods- Rhodopsin, Cones – iodopsin) involved
in the conversion of light rays into nerve
impulses.

14. Cont..
• The small area of retina where the optic nerve
leaves the eye is the optic disc or the blind
spot. It has no light sensitive cells (Rods or
Cones).

15. Cont..
• Lateral to the optic disc a depression called
macula lutea.
• The center of macula is again depressed to
form the fovea centralis. It contains cones
only and is the site of maximum acuity of
vision.

16. BLOOD SUPPLY
• Arterial blood is
supplied by branches
of ophthalmic artery
(ciliary arteries &
central retinal artery)
• Venous drainage a
number of veins
including the central
retinal vein.

17. 2. LIGHT TRANSMITTING MEDIA (OR)
REFRACTIVE MEDIA
1. Aqueous humor
2. Vitreous humor
3. Lens

19. Cont..
• The eye keeps its shape because of intraocular
pressure (15-16 mmHg) exerted by the
vitreous body and the aqueous fluid. It
remains constant throughout the life.

20. Lens
• The lens of the eyeball is crystalline in nature.
• It is situated behind the pupil.
• It is biconvex, transparent and elastic in
structure.
• Lens refracts light rays and helps to focus the
image of the object on retina.

21. Cont..
• Light from a single point of a distant object
and light from a single point of a near object
being brought to a focus by changing the
curvature of the lens.

22. Accessory Visual Structures
of The Eye

23. Accessory Visual Structures
The accessory visual structures are the
protecting and supporting structures of the
eye. It includes:-
1. Eyebrow
2. Eyelids and eyelashes
3. Conjuctiva
4. Lacrimal apparatus

24. Eyebrow
• The eyebrow is an area of thick, short hairs
above the eye.
• The main function is to prevent sweat, water,
and other debris falling into the eye, but they
are also important to human communication
and facial expressions.

25. Eyelids & Eyelashes
• The eyelids are two movable folds of tissue
situated above and below the front of each
eye.
• Shade the eyes during sleep, protect the eye
from excessive light and foreign objects, and
spread lubricating secretions over the
eyeballs.
• On their free edges, there are short curved
hairs, the eyelashes.

26. Conjuctiva
• It is a fine transparent membrane that lines
the eyelids and the front of the eyeball.
• The medial and lateral angles of the eye
where the upper and lower lids come together
are called medial canthus and lateral canthus.

27. Eyelid Margins
• Along the edges of the lids are numerous
sebaceous glands (Meibomian glands), some
with ducts opening into the hair follicles of the
eyelashes.
• They secrete an oily material, spread over the
conjuctiva by blinking, which delays
evaporation of tears.

29. Lacrimal Apparatus
For each eye, this consists of:-
• 1 lacrimal gland and its ducts
• 2 lacrimal canaliculi
• 1 lacrimal sac
• 1 nasolacrimal duct

30. Lacrimal Apparatus

31. Cont..
• The lacrimal gland is located within the orbit
above the lateral end of the eye.
• It continually releases fluid (tears) which cleanses
and lubricates eye's surface and keep it moist.
• Tears are composed of water, mineral salts,
antibodies and lysozyme.
• The tears leave the lacrimal gland by several small
ducts and pass over the front of the eye under
the lids towards the medial canthus where they
drain into the two lacrimal canaliculi; the
opening of each is called punctum.

33. Cont..
• The two canaliculi lie one above the other,
separated by a small red body, the Caruncle.
• The tears then drain into the lacrimal sac,
which is the upper expanded end of the
nasolacrimal duct.
• Nasolacrimal duct is a membranous canal
approx 2cm long, extending from the lower
part of the lacrimal sac to the nasal cavity.

34. Cont..
The fluid that fills the conjuctival sac is a
mixture of tears and the oily secretion of
mebomium glands.
The functions of this fluid include:-
a) Washing away irritating materials, eg. Dust.
b) Lysozyme prevents microbial infection.
c) Its oiliness delays evaporation and prevents
drying of the conjuctiva.

35. Six extrinsic eye muscles move each eye:
1. Lateral rectus– moves the eye out ward, away
from the nose
2. Medial rectus– moves the eye inward, toward
the nose
3. Superior rectus– moves the eye upward and
slightly outward
4. Inferior rectus– moves the eye downward and
slightly inward
5. Superior oblique– moves the eye inward and
downward
6. Inferior oblique– moves the eye outward and
upward

36. Six extrinsic eye muscles move each eye:

37. PHYSIOLOGY OF VISION

38. Physiological Events Of Vision
1. Refraction of light entering the eye
2. Focusing of image on the retina by
accommodation of lens
3. Convergence of image
4. Photo-chemical activity in retina and
conversion into neural impulse
5. Processing in brain and perception

39. 1. Refraction of light entering the eye:
• Light wave travels parallel to each other but
they bend when passes from one medium to
another. This phenomenon is called refraction.
• In normal eye, after refraction from different
mediums, light wave is focused on retina.

40. 2. Accommodation of lens to focus image:
• Accommodation is a reflex process to bring
light rays from object into perfect focus on
retina by adjusting the lens.
• When an object lying less than 6 meter away is
viewed, image formed behind retina. But due
to accommodation of lens image formed in
retina and we can see the object.

41. Cont..
• When nearer object is viewed, ciliary muscle
contract and lens become thick which causes
focus on closer object.
• When distant object is viewed, ciliary muscles
relaxes, and lens become thinner, due to
which image forms on retina.
• The normal eye is able to accommodate light
from object about 25 cm to infinity.

43. 3. Convergence of
image:
• Human eye have binocular vision, it means
although we have two eye, we perceive single
image
• In binocular vision, two eye ball turns slightly
inward to focus a close object so that both
image falls on corresponding points on retina
at same time. This phenomenon is called
convergence.

44. 4. Photo-chemical activity in retina and
conversion into neural impulse
• Each eye contains 125 million rods which contains
light sensitive pigment- rhodopsin and 7 million
cone cells which contain iodopsin.
• When light is falls on rod cell, it is absorbed by
rhodopsin and it breaks into scotopsin and 11 cis-
retinal. The process is known as bleaching.
• Hyperpolarized rod cells transmit the neural signal
to bipolar cell.
• Bipolar cell and ganglion cell process the neural
signal and generate action potential to transmit to
brain via optic nerve.

46. 5. Processing of image in brain and
perception:
• Retina contains 5 types of cells and they are
interconnected by synapse.
• These cells are photoreceptor cells (rod and
cone), bipolar cell, ganglion cell, horizontal cell
and amacrine cell.
• All visual information originates in retina due
to stimulation of rods and cones are conveyed
to brain through optic nerve.

48. Cont..
• The nerve fiber of ganglion cells from both
eyes carries impulse along two optic nerve.
• The optic nerves meets at optic chiasma
where fibers from nasal half of each retina
cross-over but fibers from temporal half of
each retina do not cross-over.
• The optic nerve after crossing the chiasma is
called as optic tract.

49. Cont..
• Each optic tract continues posteriorly and
synapse with neuron in thalamus called lateral
geniculate body which project to primary visual
cortex in occipital lobe of cerebrum and image is
perceived.

52. ERRORS OF REFRACTION
• Refraction results in the focusing of image on
the retina of the eye, permitting vision.
• In refractive errors, vision is impaired because
a shortened or elongated eyeball prevents
light rays from focusing sharply on the retina.
• Blurred vision from refractive errors can be
corrected with eyeglasses or contact lenses.

53. Types of refractive errors:
1. Myopia
2. Hypermetropia (Hyperopia)
3. Astigmatism
4. Presbyopia

54. 1. Myopia
• Near-sightedness
• Problem seeing objects far away
• Distance between lens and retina too large
• Light focused in front of retina
• Correct with concave (diverging) lenses

55. 1. Myopia

56. 2. Hypermetropia
• Far-sightedness
• Problem seeing close objects
• Distance between lens and retina too small
• Light focused behind retina
• Corrected with convex (converging) lenses

57. 2. Hypermetropia

58. 3. Astigmatism
• Eye cannot focus an object’s image on a
single point on retina
• Cornea is oval instead of spherical
• Causes blurred vision
• Some types can be corrected with
cylindrical/ oval lenses

59. 3. Astigmatism

60. 4. Presbyopia
• Presbyopia is the gradual loss of eye’s ability
to focus on nearby objects.
• It occurs due to hardening of lens due to
ageing.
• It usually becomes noticeable in early to mid-
40s and continues to worsen until around age
65 years.

61. 4. Presbyopia

62. PATHOLOGICAL TERMS
• Glaucoma- It is a group of eye conditions that
damage the optic nerve. This damage is often
caused by an abnormally high pressure in the
eye (IOP).
• Cataract- It is clouding forms in lens due to
denaturing of lens protein. It obstructs
passage of light.

63. Cont..
• Conjutivitis- Inflammation or infection of the
outer membrane of the eyeball and the inner
eyelid.
• Strabismus- Squint, also called strabismus, is
where the eyes point in different directions.