|
Eyebrows
|
prevent sweat from running into the eyes
|
|
Eyelash
|
traps dust and prevent it from running into the eyes
|
|
Eyelid
|
protect eyes from dirt and strong light
|
|
spread tears over eye surface when blinking
|
|
|
Tear gland
|
produces tears (sodium, chloride..) kills bacteria
|
|
Tear duct
|
drains tear into nasal cavity
|
|
1
|
light rays from object enters the eye
|
|
refracted and focused onto retina
|
|
|
by
|
cornea, aqueous humour, lens , vitreous humour
|
|
cornea
|
most of the refraction
|
|
lens
|
fine focusing
|
|
2
|
real and inverted image formed on retina
|
|
3
|
photoreceptors stimulated by light generate nerve impulse
|
|
nerve impulse travel along optic nerve to visual centre
|
|
|
4
|
visual centre in cerebrum interpret nerve impulse as an upright image of object
|
|
Orbit
|
socket in the skull
|
|
attached by 3 pairs of eye muscles
|
|
|
3 eye muscles
|
allow eyeball to rotate in different direction
|
|
Conjunctiva
|
transparent membrane
|
|
keeps front of eyes lubricated and moist
|
|
Rod cells
|
Cone cells
|
|
more numerous
|
less numerous
|
|
sensitive to low light intensity
|
sensitive to high light intensity
|
|
important for dim light vision
|
important for bright light vision
|
|
black and white vision
|
color vision (red, green, blue)
|
|
Rod cells
|
periphery of the retina
|
|
none at yellow spot and blind spot
|
|
|
Cone cells
|
concentrated at yellow spot
|
|
a few present on periphery of retina
|
|
Sclera
|
tough white coat
|
|
protects inner structure
|
|
|
maintain shape of eyeball
|
|
|
surface for the attachment of eye muscle
|
|
|
Cornea
|
transparent layer of tissue
|
|
allows light to enter the eye
|
|
|
a curved surface to help refract and focus light on retina
|
|
|
no capillaries since it obtains nutrients from aqueous humour
|
|
|
Choroid
|
middle layer of eyeball
|
|
contains black pigment that absorbs light
|
|
|
pigment reduces reflection of light within the eye and helps form sharp images
|
|
|
rich in capillaries as it supplies nutrients to sclera and retina
|
|
|
Iris
|
continuous with the choroid
|
|
made up of muscles which controls the size of pupil to regulate the amount of light entering the eyes
|
|
|
contains pigment that determine the colour of iris
|
|
|
Pupil
|
an opening at centre of the iris
|
|
allows light to enter the eyes
|
|
|
size is controlled by iris
|
|
|
Retina
|
innermost layer of eyeball
|
|
contains many photoreceptors and nerve fibres
|
|
|
photoreceptors : rod or cone cells
|
|
|
Optic nerves
|
nerve fibres in retina grouped
|
|
transmits nerve impulses from photoreceptors to cerebrum of brain
|
|
|
Yellow spot
|
high density of cone cells
|
|
no rod cells
|
|
|
Blind spot
|
no photoreceptors
|
|
Lens
|
transparent , elastic , biconvex
|
|
refracts and focuses light on retina
|
|
|
thickness adjusted by ciliary body
|
|
|
living cells with no nuclei
|
|
|
no capillaries as it obtains nutrients from aqueous humour
|
|
|
Suspensory ligament
|
connected to ciliary body
|
|
Ciliary body
|
contains ciliary muscles
|
|
controls tension of suspeonsory ligaments
|
|
|
controls thickness of lens
|
|
|
Aqueous humour
|
watery fluid produced by ciliary body between cornea and lens
|
|
supplies nutrients and o2 to cornea and lens by diffusion
|
|
|
Vitreous humour
|
jelly like fluid between lens and retina
|
|
Both
|
refracts lights on retina
|
|
maintain shape of eyeball
|
|
Light rays (distant)
|
parallel
|
|
Light rays (near)
|
come from the same point of object
|
|
Reminders
|
add arrows
|
|
dotted lines behind retina
|
|
Circular muscles of iris
|
relaxes
|
|
Radial muscles
|
contracts
|
|
Pupil
|
dilates
|
|
Result
|
more light enters eyes
|
|
Importance
|
allow photoreceptors to be stimulated so a clear image forms
|
|
Circular muscles of iris
|
contracts
|
|
Radial muscles
|
relaxes
|
|
Pupil
|
constricts
|
|
Result
|
less light to enter eye
|
|
Importance
|
prevent photoreceptors from being damaged by bright light
|
|
Ciliary muscles
|
contract
|
|
Tension
|
reduced
|
|
Suspensory ligaments
|
slackened
|
|
Lens
|
thicker (more convex)
|
|
refracts more light
|
|
|
Eye strains
|
ciliary muscles contracting for a long time
|
|
Ciliary muscles
|
relaxes
|
|
Tension
|
increases
|
|
Suspensory ligaments
|
tightened
|
|
Lens
|
thinner (less convex)
|
|
refracts light less
|
|
Vision problem
|
cannot see distant object clearly
|
|
Cause
|
lens too thick
|
|
eyeball too long
|
|
|
Image
|
formed in front of retina
|
|
Correction
|
concave lenses (diverges light)
|
|
Vision problem
|
cannot see near objects clearly
|
|
Cause
|
lens too thin
|
|
eyeball too short
|
|
|
Image
|
formed behind the retina
|
|
Correction
|
convex lens (converge light)
|
|
Problem
|
cannot distinguish colors
|
|
Cause
|
deficiency of one or more cone cells
|
|
Correction
|
no cure
|
|
wear lenses
|
No comments yet.
Cheatography n. The art of mapping complex subjects into clear, instantly navigable reference guides.
