the eye: structure & function
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The Eye: Structure & Function. 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 - PowerPoint PPT PresentationTRANSCRIPT
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The Eye: Structure & Function
The eye contains photoreceptors; rods & cones which perceive light stimulus
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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
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Eye lashes
Sclera
Pupil
Iris
Eye lid
External Structure of the eye
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Internal Structure of the Eyesclera
choroids
retina
ciliary body / muscles
iris
lens
cornea
fovea
blind spot
optic nerve
pupil
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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.
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The retina: contains rods & conesdi
rect
ion
of li
ght
mov
emen
t
Pigment
Cone
Rod
Bipolar cell
Ganglion cell
Synapse
Sclera
Axon of the ganglion cell
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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
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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
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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
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Pupil reflex – pupil dilation & constriction
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Pupil reflex
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Pupil dilation
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
radialcircular
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Pupil constriction
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
radialcircular