biology ~ structure of the eye Flashcards
what does the iris control?
changes size of the pupil to control how much light enters the eye
what do the ciliary muscles control?
controls shape of lens
what does the cornea do?
refracts light as it enters the eye
what is the sclera?
protective outer layer
what does the retina do?
light sensitive layer
containing light receptor cells
(rods + cones)
what does the optic nerve do?
carries nerve impulses from the light receptors to the brain
what is the eye?
a sense organ containing receptors sensitive to light intensity an colour
what happens to the eye in low light intensity?
pupil size ~ dilated
circular muscles ~ relaxes
radial muscle ~ contracts
what happens to the eye in high light intensity?
pupil size ~ constricted
circular muscle ~ contracts
radial muscle ~ relaxes
how does the eye change when in bright light
light rays reflect off of the object and into the eye
the cornea and lens refracts the light rays onto the retina
the light receptors detect the light
they generate an electrical impulse that is sent along the optic nerve to the relay neurone
the electrical impulse travels along the motor neurone to the circular muscles in the iris which contract
the pupil becomes constricted
what is the order of neurone in a reflex?
sensory neurone
relay neurone
motor neurone
what does the cornea do to the light?
the cornea refracts the light and then the lens refracts it further so that the light rays focus on the retina
when the eye focuses on a distant object:
ciliary muscles = relax
suspension ligaments = pulled tight
lens = pulled thin and slightly refracts
when the eye focuses on a near object:
ciliary muscles = contract
suspensory ligaments = loosen
lens = get thicker and refract strongly
what is hyperopia?
someone who is long sighted can see distant objects clearly but they cannot focus on near objects clearly
the lens focuses the light behind the retina
what is myopia?
someone who is short sighted can see near objects clearly but they cannot focus on distant objects clearly
the lens focuses the light in front of the retina
what is normal vision?
the image is formed at the back of the retina, mostly at the fovea
this happens because light is correctly refracted by the cornea, lens and humours in the eye
you don’t need to fix this
how to fix myopia eyesight:
the image is formed in front of the retina
this happens because the lens is too strong, or the eyeball is too long
you can use a concave lens to correct this
how to fix hyperopia eyesight:
the image is formed behind the retina
this happens because the lens is too weak or the eyeball is too short
you can use a convex lens to correct this
what are the 2 different types of lenses?
convex ~ converging lens (oval shape)
concave ~ diverging lens (hourglass shape)
