The Eye: Structure & Function

The eye contains photoreceptors; rods & cones which perceive light stimulus

Functions of the eyethe eye allows us to see &

interpret the shapes, colors and dimensions of objects in the world by processing the light they reflect

eyes are sense organs that detect and respond to light stimulus giving us sense of sight

they contain photoreceptors; rods & cones located in the retina

rods & cones detects light stimuli & converts light energy to nerve impulses which are transmitted to the brain for interpretation

Structure of the human eye

Structure and Working of Human Eye

Eye lashes

Sclera

Pupil

Iris

Eye lid

External Structure of the eye

Internal Structure of the Eyesclera

choroids

retina

ciliary body / muscles

iris

lens

cornea

fovea

blind spot

optic nerve

pupil

Structure

Sclera

Choroid

RetinaCiliary Body

Iris

Pupil

Lens

Cornea

Fovea

Blind SpotOptic Nerve

Function(s)

tough outer layer of the eye which overs and protect eyeball. prevents internal reflection of light and nourish retina. contains rods and cones which convert light into nerve impulses. a ring of muscle controlling the shape and curvature of the lens.

controls the pupil size thus controls entry of light.

a hole in the iris that lets light into the back of the eye.

accommodation & focusing of light onto the retina.

bends incoming light focusing it on the retina.

a tiny area of densely packed cones for detailed and coloured vision. exit point of the optic nerve cutting through the retina so no rods or cones carries the impulses from the rods and cones to the visual center of the brain.

The retina: contains rods & conesdi

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Pigment

Cone

Rod

Bipolar cell

Ganglion cell

Synapse

Sclera

Axon of the ganglion cell

Physiology of the Eye

Image formation on the retinalight from an object forms a

focused image on the retinathe curved surfaces of the

cornea & lens bends the light rays as they pass through them

an image which is smaller than the object is formed upside-down on the retina

the cornea & vitreous humours are mainly responsible for bending of rays of light – refraction while the lens does the final adjustments to focus

lens is elastic & flexible thus it is able to change its shape

Accommodation

the ability of the eye to alter its focus so that clear images of both close and distant objects can be formed on the retina

the shape of the lens can be altered by suspensory ligaments and the ciliary muscles

thickening & thinning of the lens adjusts the focus

Focusing: bending of light rays to fall on the retinaDistance Vision Near Vision

ciliary muscle relaxes suspensory ligament stretched

by outward pressure of the humours on the sclera

the lens is pulled thin light from a distant object is

focused on the retina – the eye is accommodate i.e. focused for a a distant object

ciliary muscle contracts suspensory ligament slackens

because the ciliary contracts to a smaller circle taking away the tension out of suspensory ligament

the lens is allowed to thicken light from a near object is focused

on the retina – the eye is accommodate i.e. focused for a near object

Light rays form far object

Light rays from near object

Pupil reflex – pupil dilation & constriction

Pupil reflex

Pupil dilation

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PUPIL DILATED

The pupil is the dark space in the centre of the iris

The iris contains circular and radial muscles and their activity can change pupil diameter

In dim light, the circular muscles relax & the radial muscles contract, the pupil dilates i.e. widens so that much light is able to reach the retina

radialcircular

Pupil constriction

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PUPIL CONSTRICTED

The pupil is the dark space in the centre of the iris

The iris contains circular and radial muscles and their activity can change pupil diameter

In bright light, the circular muscles contract, & the radial muscles relax, pupil constricts i.e. narrows so that less light reaches the retina to avoid damage

radialcircular