1. ARAVIND EYE CARE SYSTEM Aravind Eye Hospital & Postgraduate Institute of Ophthalmology ARAVIND EYE CARE SYSTEM Aravind Eye Hospital & Postgraduate Institute of Ophthalmology DEPARTMENT OF COUNSELLING Basic Anatomy & Physiology of the eye

2.  The eye serves like camera, capturing the scenes before it.  The eyes are placed safe in a socket in the skull and are protected by the eyelids  Our eyes are more efficient than a film in a camera, capturing the scenes and sending it to the brain.  The eye is spherical in shape.

3.  There are 6 extra ocular muscles present outside of the eye which help in the movement of eyes in various directions.  The extra ocular muscles are supplied by nerves from the brain.  The eye ball is connected to the brain through a nerve called optic nerve.

4.  Eye lids  Conjunctiva  Cornea  Anterior chamber  Iris  Pupil  Lens  Vitreous gel Anatomy of the eye

5. Eyelids  There are two eye lids – The upper eye lid and lower eye lid  The torsal plate helps in giving the structure to the eye lid  The eye lids protect the eyes from external environmental pollution

6. Picture with muscles  Muscles connected to the eye which are called extra ocular muscles, and are present outside the eye.  Superior rectus  Medical rectus  Lateral rectus  Inferior rectus  Superior oblique  Inferior oblique

7. Conjunctiva   This is a thin white membrane with blood vessels covering the eye ballCornea   The cornea is transparent   It is like a window to the eye   Cornea measures about 11.5 mm in horizontal length   There are five layers in cornea

8. Anterior Chamber   The space between the cornea and Iris is called the anterior chamber filled with aqueous humour, which is secreated by a structure called ciliary body   The depth of anterior chamber is 2.5 mm   When the aqueous pressure in the eye increases the condition is called Glaucoma

9. Iris & Pupil  Behind the cornea there is a brown circular diaphragm like structure called the Iris  It consists of two types of muscles – Circular muscles & Radial muscles  The central opening of the Iris is called the pupil  Normal size of pupil is 2-3 mm  Depending on the intensity of light, the size of the pupil increases or decreases in size

10. Lens  Behind the Iris is situated, a transparent structure called the lens  The nutrition to the lens is supplied by the aqueous humour  The shape of the lens is altered to see object at near and distance  Light rays passes through the lens and falls on the retina  When the lens looses it transparency it becomes an opaque structure, through which light cannot pass. This condition is called as cataract

11. Vitreous gel  There is a colorless, transparent gel like substance behind the lens  The vitreous gel is like the white of an egg giving shape to the eye

12. The coats of the eye  There are 3 coats of the eye  Sclera  Choroid  Retina Sclera  The outer coat is the sclera, which is covered by conjunctiva, a thin white membranous tissue  The extra ocular muscles are inserted to the sclera

13. Choroid  The choroid layer is middle coat situated between sclera and retina  The choroids tissue is dark brown in colour due to vascularity  It supplies nutrition to retina, vitreous and other sensitive structures of the eye  It also prevents the scattering of light

14. Retina  The retina is made up of ten layers of neuronal tissues  The retina is the inner most structure of the eye  The rays coming from the objects fall on the retina  Retina is basically transparent, cellophane, like tissue  The optic disc is the head of the optic nerve entering the eye  Arteries and veins course through the retina

15.  Macula is the most visually scientific part of retina  It is pink in colour with a central depression called the optic disc cup  In diseases like glaucoma where the pressure in the eye is raised this cup is enlarged

16.  Retinal Pigment epithelium  Layers of rods and cones  External limiting membrane  Outer nuclear layer  Outer Plexiform layer  Inner nuclear layer  Inner Plexiform layer  Ganglion cell layer  Nerve fiber layer  Internal – limiting membrane

17.  The retinal receptors are divided into two main populations – the rods and the cones  The rods functions best in dim light (night)  The cones functions best under daylight conditions  The cones are far fewer in number than the rods, numbering 6 million, whereas the rods number 125 millions  Cones enable us to see small visual details with great acuity

18.  Vision with rods is relatively poor  Colour vision is totally dependent on the integrity of the cones  The cones from a concentrate area in the retina known as the forea, which lies in the centre of the macula lutea  The junction of the periphery of the retina and the ciliary body is called the Ora serratta

19.  The ability to see is an amazing process, made possible by the parts of the eye working conjunction, with one another and with the brain  Light enters the eye through the transparent cornea, gets refracted and then passes through the pupil to reach the cones  The pupil acts like the shutter of a camera  In bright light, it becomes smaller, thus restricting the amount of light entering the eye Functions of the eye

20.  In less bright illumination and in darkness, the pupil becomes larger, thus allowing adequate light to enter the eye  After light enters the pupil it passes through the crystalline lens  The refracted light then passes through the vitreous, humour to reach the retina  Here the light impulses are converted to electrical impulses and then fed into the optic nerve, which carries them to the visual centre in the brain through a complex bundle of inter connected nerve channels

21.  The brain processes these impulses to create the visual image we perceive  Retina contains 3 corresponding types of cells (cones) which respond to these three colours  A defect in colour vision is called as colour blindness. This can be partial, or total  When we look at particular object, a lot of other objects surrounding it are also perceived

22.  Hence our vision is not a small circle that we focus on but a field in which we see multiple object  The visual field has two parts: The central visual field which is the area immediate to the object we are looking at and a peripheral visual field which includes the rest of the area surrounding the central field  The eye balls are constantly in motion-up and down, and either side

23.  This is facilitated by a group of six muscles, where movements are synchronized by interconnections in the brain to produce conjugate movement Ex: When we look to the right side the right eye ball, moves outward whereas the left eyeball moves inward  An imbalance in this harmony result in a disfigurment called squint or cross – eye.