B10.5 - The Eye Flashcards
sclera
-white outer layer of eye
-tough
-transparent front area (cornea)
cornea
-transparent
-curved surface
purpose of cornea transparency
lets light in
purpose of cornea curved surface
-allows rays to change direction and enter
-ensures rays focus on retina
iris
-muscle
-controls size of pupil
pupil
hole light enters through
pupil in dim light
-enlarged = max light
pupil in bright light
-iris shrinks = less light
-so light sensitive cells are not damaged
lens
-clear disc = light passes
-held in place by ciliary muscles and suspensory ligaments
lens purpose
-fine tunes focus of light rays
-changes their direction = focuses on retina = clear image
-
ciliary muscles
contract and relax to change shape of lens
-moderate light intake
suspensory ligaments
connects lens to ciliary muscles
retina
-light enter and stimulates light-sensitive cells
-sends impulses to brain along sensory neurones in optic nerve
-brain = visual image
blurry images are made by
light focusing in front or behind the retina
refraction of rays
-cornea helps to direct rays onto retina
-rays always refract the same amount
-lens refracts light
near sight
light is spreading out very strongly from close objects
far sight
light from distant objects = parallel rays
accomodation
process of changing shape of lens to focus on near/far objects
focus on distant objects
-ciliary muscles relax
-suspensory ligaments are tight
-lens is pulled thin
-refracts light slightly as it is a distant object
Viewing near objects
-ciliary muscles contract
-suspensory ligaments loosen
-lens is thicker and curved
-refracts rays strongly
aging on eye
lens hardens
accommodation becomes harder
-not easy to focus on close objects
myopia
short sightedness
-can see close objects but not far ones
causes of myopia
-light is focused in front of retina = blurry
-lens is too curved or long eyeball
Too thick
treatment of myopia
-glasses with concave lens
-spread light from distance before it reaches retina
-unfocus the light before entering
hyperopia
-can focus on distant objects but not close ones
-light is focused behind retina
Hyperopia cause
-lens is too flat/thin
-short eyeball
-lens cannot refract light strongly enough
treatment of hyperopia
-glasses with convex lens
-brings rays together before enters eye
-can focus rays onto retina
Eye defects
hyperopia
myopia
contact lenses and pros
-placed on surface of eye
-cannot be seen = better for sport
-hard contacts = durable material
-soft contacts = flexible and comfortable
laser eye surgery
only for adults when eye stops growing
-treats myopia
-reduces thickness of cornea = refracts light less strongly
-to treat hyperopia lasers change curve of cornea
replacement lens treatment
-add another lens into eye to correct defect
-1 = faulty lens is replaced by artificial lens
-2 = contact lens is implanted into eye + natural lens is left in eye
Risks of replacement lens treatment
-damage to retina
-cataracts develop
-infections
Distant object refraction of ray
Light from distant object is only focused a small amount
-more parallel than rays from near objects
Hyperopia in the elderly
Less elastic
-cannot become thick enough to focus on near objects
