anatomy and physiology of eye

anatomy and physiology of eye

1. Chapter
Chapter
:9
:9
Anatomy
Anatomy


and
and


Physiology
Physiology


of
of


Eye
Eye
Presented by: Prof.Mirza Anwar Baig
Presented by: Prof.Mirza Anwar Baig
Anjuman-I-Islam's Kalsekar Technical Campus
Anjuman-I-Islam's Kalsekar Technical Campus
School of Pharmacy,New Pavel,Navi
School of Pharmacy,New Pavel,Navi
Mumbai,Maharashtra
Mumbai,Maharashtra
1
1

2. Overview
•
The eye is supplied by the optic nerve (2nd cranial
nerve).
•
It is almost spherical in shape and is about 2.5 cm in
•
diameter.
•
It is possible to see with only one eye but three-
dimensional vision is impaired when only one eye is
used, especially in relation to the judgement of
distance.

3. Acessory structures of eye:

4. Acessory organs of eye:

5. Secretion of lacrimal fluid:

6. Functions
•
The fluid that fills the conjunctival sac consists of
tears and the oily secretion of tarsal glands and is
spread over the cornea by blinking.
•
The functions of this mixture of fluids include:
1.
Washing away irritating materials, e.g. dust, grit
2.
The bacteriocidal enzyme lysozyme prevents
microbial infection
3. Oiliness delays evaporation and prevents drying
of the conjunctiva
4. Nourishment of the cornea.

7. Structure of eye:

8. Anatomical features:
1. Sclera
•
The sclera, or white of the eye.
•
It consists of a firm fibrous membrane that
maintains
the shape of
the eye and
gives
attachment to the extraocular or extrinsic muscles
of the eye.
2. Cornea
•
Light rays pass through the cornea to reach the retina.
•
The cornea is convex anteriorly.
•
Involved in
refracting or bending light rays
to focus them on the
retina.
3. Choroid
•
The choroid lines the posterior five-sixths of the inner surface of the
sclera.
•
Very rich in blood vessels and is deep chocolate brown in colour.
•
Light enters the eye through the pupil, stimulates the nerve endings
in the retina and is
then absorbed
by the choroid.

9. 4. Ciliary body
•
Consisting of
ciliary muscle
(smooth muscle fibres) and
secretory
epithelial cells.
•
Contraction and relaxation
of the ciliary muscle changes the
thickness of the lens which bends, or refracts light rays entering the
eye to focus them on the retina.
•
The epithelial cells secrete aqueous fluid
into the anterior segment of
the eye, i.e. the space between the lens and the cornea (anterior and
posterior chambers).
•
The ciliary body is supplied by parasympathetic branches of the
oculomotor nerve
(3rd cranial nerve)
.
•
Stimulation causes contraction of the smooth muscle and
accommodation of the eye.
5. Iris:
•
visible coloured part of the eye.
•
It is a circular body
composed of pigment cells and two layers of
smooth muscle fibres
, one circular and the other radiating. In the
centre there is an aperture called the pupil.
•
The
iris is supplied by parasympathetic and sympathetic nerves
.
Parasympathetic stimulation constricts the pupil and sympathetic
stimulation dilates it

10. Contraction and relaxation of circular and radial
muscles:

11. Retina:
1.
Innermost layer,extremely delicate structure
and is especially
adapted for stimulation by light rays.
2.
It is composed of
several layers of nerve cell bodies and their
axons,
lying on a pigmented layer of epithelial cells which
attach it to the choroid.
3. The layer highly sensitive to light is the
layer of sensory
receptor cells: rods and cones.
4. Near the centre of the posterior part is the
macula lutea, or
yellow spot.
5. In the centre of the area there is a little depression called
the
fovea centralis
, consisting of only cone-shaped cells.
6. Towards the anterior part of the retina there are fewer
cone- than rod-shaped cells.
7. The
rods and cones contain photosensitive pigments
that convert
light rays into nerve impulses.
8. The small area of retina where the optic nerve leaves the eye is
the
optic disc or blind spot.
It has no light-sensitive cells.

12. Interior of the eye:
1.
The anterior segment of the eye, i.e. the space between
the
cornea and the lens, is incompletely divided into
anterior and posterior chambers
by the iris .
2. Both chambers
contain a clear aqueous fluid
(humour)
secreted into the posterior chamber by ciliary glands.
3. It
circulates
in front of the lens, through the pupil into
the anterior chamber and
returns
to the venous
circulation through the scleral venous sinus (canal of
Schlemm) in the angle between the iris and cornea.
4. There is
continuous
production and drainage but the
intraocular pressure remains fairly constant between 1.3
and 2.6 kPa (10 to 20 mmHg).
5. An increase in this pressure causes
glaucoma
. Aqueous
fluid
supplies
nutrients and removes waste from the
transparent structures in the front of the eye that have
no blood supply, i.e. the cornea, lens and lens capsule.

13. Physiology of vision

14. Structure of retina:

15. Structure of retina:

16. The cyclical bleaching and regeneration of
photopigment

17. Light and dark adaptation