The eye contains photoreceptors; rods & cones which
perceive light stimulus
Functions of the eye
 the 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
External Structure of the eye
Eye lashes
Sclera
Pupil
Iris
Eye lid
Internal Structure of the Eye
sclera
choroids
retina
ciliary body / muscles
iris
lens
cornea
fovea
blind spot
optic nerve
pupil
Structure
Function(s)
Sclera
tough outer layer of the eye which overs and protect eyeball.
Choroid
prevents internal reflection of light and nourish retina.
Retina
contains rods and cones which convert light into nerve impulses.
Ciliary Body
a ring of muscle controlling the shape and curvature of the lens.
Iris
controls the pupil size thus controls entry of light.
Pupil
a hole in the iris that lets light into the back of the eye.
Lens
accommodation & focusing of light onto the retina.
Cornea
bends incoming light focusing it on the retina.
Fovea
a tiny area of densely packed cones for detailed and coloured vision.
Blind Spot
exit point of the optic nerve cutting through the retina so no rods or
cones
Optic Nerve
carries the impulses from the rods and cones to the visual center of the
brain.
The retina: contains rods & cones
direction of light movement
Axon of the ganglion cell
Ganglion cell
Bipolar cell
Synapse
Rod
Cone
Pigment
Sclera
Physiology of the Eye
Image formation on the retina
 light from an object forms a




focused image on the retina
the 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 upsidedown 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 retina
Distance Vision
Near Vision
Light rays from
near object
Light rays form
far object
 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
Pupil reflex – pupil dilation & constriction
Pupil reflex
Pupil dilation
radial
circular
CLICK TO
CONSTRICT
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
Pupil constriction
radial
circular
CLICK TO
DILATE
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