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The eye class notes

THE EYE

The eye class notes

THE EYE
The eye is a complex sense organ, whose functions is to receive light by which an
animal perceives and distinguishes objects in its immediate environment
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The orbit provides protection against
physical damage and has a fatty layer lining that provides further protection as a
shock absorber against mechanical injury
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The lateral muscles
move the eye left and right while the superior and inferior rectus muscles move the
eye up and down and the oblique muscles steady the eye in its up and down
movement
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The eyebrows are thickly covered with
hair to prevent sweat and dust from entering the eye
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The eye comprises of three distinct layers:
1
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The middle layer or choroid
3
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The sclera continuous and forms the
cornea
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The front portion of the
cornea is a thin transparent membrane called conjunctiva which continuous with
the epithelium of the eye lid
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Its function is to absorb stray light thus preventing reflection within
the eye
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The iris is a thin round sheet of muscular tissues
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Is also
pigmented to give the eye its colour
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It mostly
appears round
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Contains circular and smooth muscles which contract and relax to
alter the shape of the lens
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LENS
It is transparent biconvex structure located immediately behind the pupil of the
eye
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They become taut or loose
to alter the shape of the lens
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The anterior chamber (part behind the cornea) is filled with a watery fluid called
the aqueous humour
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The
fluids help maintain the spherical shape of the eyeball and refract the incoming
light towards the retina
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An outer pigmented region in contact with the choroid
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A middle region of photoreceptors consisting of cones and rods
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An inner region of neutrons
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CONES AND RODS
Cones contain a photochemical pigment called iodopsin which perceives light of
high intensity
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This breakdown results into depolarization of the cell membrane of the cones thus
generating a nerve impulse that is transmitted along the neurons to the optic nerve,
which then transmits the impulses to the brain for interpretation
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This property allows them to have high visual
activity (ability to distinguish objects clearly)
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Rods have retinal convergence thus
have low visual activity and cannot distinguish fine details
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The amount of rhodopsin in the rods is increased in the dark
to raise the sensitivity of the rods to dim light
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The area where
the optic nerve enters the eyeball is called the blind spot
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EYE DEFECTS
There are mainly two types of eye defects:
1
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Hyperopia
MYOPIA (NEARSIGHTED)
Refers to when a person can see nearby objects clearly but is unable to see objects
beyond some distance
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It causes the light rays to focus at the point in front pf
the retina rather than directly on the surface
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HYPEROPIA (FARSIGHTED)
The person can see far objects clearly but is unable to see the nearby objects
clearly
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This vision problem occurs
when the light rays entering the eye focus behind the retina rather than directly on
it
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The eye class notes

CATARACTS
It is an eye defect associated with old age
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In this condition the eye lens becomes
cloudy hence blocking transmission of light rays
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COLOUR BLINDNESS
Is a genetic defect in which certain colours cannot be distinguished by human
beings
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