B5: THE EYE Flashcards
What is the sclera?
-white outer layer of the eye
-tough and strong so eyeball isn’t easily damaged
What is the cornea?
-transparent outer layer
-refracts light into eye
What is the iris?
-muscle which controls the size of the pupil and therefore how much light enters the eye
What is the lens?
-focuses light onto the retina (which contains receptor cells sensitive to light intensity and colour)
-shape of the lens is controlled by the ciliary muscles and suspensory ligaments
What is the optic nerve?
-carries impulses from the receptors on the retina to the brain
Iris reflex in bright light
-circular muscles contract
-radial muscles relax
-pupil becomes smaller so less light enters the eye
Iris reflex in dim light
-circular muscles relax
-radial muscles contract
-pupil becomes wider to allow more light to enter the eye
What is accommodation?
the process of changing the shape on the lens to focus on near/distant objects by focusing light on the retina
What happens when looking at near objects?
-ciliary muscles contract
-suspensory ligaments slacken
-lens is fat and more curved
-light refracts more
What happens when looking at distant objects?
-ciliary muscles relax
-suspensory ligaments become taut
-lens is thin and less curved
-light refracts less
What is myopia?
short sightedness (unable to focus on distant objects)
What is hyperopia?
long sightedness (unable to focus on near objects)
What are the causes of myopia?
-lens is wrong shape (light refracted too much)
OR
-eyeball is too long (image of distant object brought into focus in front of retina)
What are the causes of hyperopia?
-lens is wrong shape (light not refracted enough)
OR
-eyeball is too short (image of near object brought into focus behind retina
How is myopia treated?
glasses with concave lens (refracts light less to focus on retina)
