STRUCTURE & FUNCTION OF EYE

INTRODUCTION

Gift of the CreatorGives us the sense of sight70% of all sensory receptors are

in the eyeSpheroid structure, about 2/3 the

size of a ping-pong ballFunctions: distinguishes light and

dark, shape, colour, brightness & distance of objects.

EXTERNAL STRUCTURE OF EYE

Includes : bony orbit, eyelids, eyelashes, tears and fat glands, extra ocular muscles, conjunctiva

BONY ORBIT/EYE SOCKET

Most of the eye is enclosed in a bony orbit

Structure:o Cheekboneo Foreheado Templeo Side of noseFunction:Provides protection to the eye

EYELIDS

A thin fold of skin that covers the eye Protect eye from foreign matter (dust, dirt,

debris) Protect against bright light that might

damage the eye Lubricate the eye surface by distributing

tears over the corneaUpper eyelid

Lower eyelid

EYELASHES

Are the hairs that grow at the edge of eyelidsProtect the eye by filtering out foreign matter

CONJUNCTIVA

A thin, clear layer of skin Lines the inner surface of eyelids & covers the front surface of the eyeball except the cornea Secretes mucus to lubricate the eye Keeps bacteria and foreignmaterial from getting behind eye

INNER LAYER

STRUCTURE OF RETINA

Innermost, sensitive layer of the eye

A delicate membrane containing photoreceptors & associated neurons

PHOTORECEPTORS

Are of two main kinds:RodsCones

RODS

Sensitive to dim lightPresent everywhere in the retina except the foveaAllow dim light vision & peripheral vision125 million rods in the average retina

CONES

Sensitive to bright lightClustered near the centre of retina(fovea)Distinguish colours & allowsharp vision5 million cones in the average retina

FOVEA

A depression in the retina directly opposite to lens

Fovea (cont.)

Contains only cones & no rods

Function: to form an extremely clear image

Is directed towards whatever object you are studying most closely

OPTIC DISC/BLIND SPOT

A point where the optic nerve enters retina

Optic disc

Optic nerve

BLIND SPOT

absence of cones & rods at the optic discNo vision is possible hereReferred to as blind spot

OPTIC NERVE

The bundle of over one billion nerve fibres that carry visual messages from the retina to the brain.

RETINAL BLOOD VESSELS

Arteries transmit oxygen & nutrients

Veins carry deoxygenated blood from the eye

FUNCTION OF RETINA

Transforms light energy to electrical signals

CHAMBERS OF EYE

Anterior Chamber

Posterior Chamber

AQUEOUS HUMOUR

A clear, watery fluid in the anterior chamber

Nourishes the lens & cornea and helps refract light onto the retina

VITREOUS HUMOUR

A clear, gel-like fluid in the posterior chamber

Supports the lens & retina and keeps the eye from collapsing

Aids the magnifying power of the eye

WORKING OF THE EYE

Light rays coming from object enter through the cornea, progress through pupil & fall on eye lens which converts light rays & produces a real & inverted image of object on retina. The image thus formed is conveyed to brain by optic nerve in the form of electrical signals which are seen by the brain as a visual image.