Eye Flashcards
functions have eyelids
protect cornea from mechanical damage
squinting to prevent excess light from entering the eye and damaging the retina
help spread tears over the cornea and conjunctiva and wipes dust particles off the cornea by blinking
eyelashes
help shield eye from dust particles
Tear glands
secrete tears to wash away dust particles
keep cornea moist for atmospheric oxygen to dissolve so that oxygen can diffuse into the cornea
lubricate the conjuctiva helping to reduce friction when eyelids move
conjuctiva
helps to secrete mucus to keep front of the eyeball moist
sclera
tough white outer covering of eyeball which protects eyeball from mechanical damage
choroid
contains black pigments to prevent internal reflection of light
contains blood vessels that bring oxygen and nutrients to the eyeball and remove metabolic waste
retina
light sensitive layer containing photoreceptors where images are formed
cornea
transparent layer in front of eye continuous with sclera which refracts light towards lens
iris
consist two sets of involuntary muscles, circular and radial muscles surrounding pupil. adjusts the amount of light entering the eye by changing size of pupil
pupil
hole in the centre of the iris appears black because choroid is visible through it allowing light to enter the eye
lens
transparent, biconvex, elastic crystalline body changes curvature or thickness to refract light onto the retina
suspensory ligaments
connective tissue. attach edge of lens to ciliary body. transfer the effect of ciliary muscles to the lens to control its shape
ciliary body
consists of ciliary muscles. muscles contract and relax to control the curvature or thickness of the lens
aqueous humour
transparent water fluid which refracts light onto lens and keeps eyeball firm
serves as a medium for diffusion of oxygen and nutrients
vitreous humour
transparent jelly like fluid which refracts light onto retina and keeps eyeball firm
Fovea
part of retina where images are mainly focused
gives detailed colour vision in bright light
blind spot
found over the optic nerve with no photoreceptors. an area on the retina where neurones leave the eye
optic nerve
composed of sensory neurones which transmits nerve impulses from photoreceptors to brain
what is accommodation
is the adjustment of lens to change curvature or thickness so that clear images at different distances are formed on the retina
what happens when you focus on near object
ciliary muscles contract reducing pull on suspensory ligaments. suspensory ligaments slacken. lens becomes thicker and more convex decreasing its focal length. light rays from the near object are brought to focus on the retina. photoreceptors are stimulated and nerve impulses are produced and transmitted to the brain via optic nerve
what happens when you focus on a far object
ciliary muscles expand pulling on suspensory ligaments. suspensory ligaments become taut. lens become thinner and longer. focal length increases. light rays on distant object is focused on the retina. photoreceptors are stimulated and nerve impulses are generated and transmitted to the brain via the optic nerve
pupil reflex in bright light
photoreceptors in the retina detect an increase in light intensity.
nerve impulses are sent along the sensory neurone in optic nerve to the brain. Brain returns impulses along the motor neurone to the circular and radial muscles of the iris. circular iris muscles contract while radial iris muscles relax. diameter of pupil decreases allowing less light to enter.
pupil reflex in dim light
photoreceptors detect decrease in light intensity. nerve impulses sent along sensory neurones in optic nerve to the brain. the brain returns impulses along the motor neurone to the circular and radial muscles of the iris. the circular iris muscles relax while radial iris muscles contract. the diameter of the pupil increases allowing more light to enter
