ChapterChapter :9 :9

AnatomyAnatomy andand PhysiologyPhysiology ofof EyeEye

Presented by: Prof.Mirza Anwar BaigPresented by: Prof.Mirza Anwar Baig

Anjuman-I-Islam's Kalsekar Technical CampusAnjuman-I-Islam's Kalsekar Technical CampusSchool of Pharmacy,New Pavel,Navi School of Pharmacy,New Pavel,Navi

Mumbai,MaharashtraMumbai,Maharashtra

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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 ofdistance.

Acessory structures of eye:

Acessory organs of eye:

Secretion of lacrimal fluid:

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, grit2. The bacteriocidal enzyme lysozyme prevents

microbial infection3. Oiliness delays evaporation and prevents drying

of the conjunctiva4. Nourishment of the cornea.

Structure of eye:

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.

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

Contraction and relaxation of circular and radial muscles:

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 calledthe fovea centralis, consisting of only cone-shaped cells.

6. Towards the anterior part of the retina there are fewercone- 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.

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.

Physiology of vision

Structure of retina:

Structure of retina:

The cyclical bleaching and regeneration ofphotopigment

Light and dark adaptation