structure of eyes Flashcards
eye with far object
incoming light is parallel ciliary muscles relax suspensory ligaments are tight lens is pulled thin light is refracted less light converges on the retina
eye with near object
incoming light is divergent ciliary muscles contract suspensory ligaments are loose lens becomes fat light is refracted more light converges on retina
what are sense organs?
groups of receptor cells responding to different stimuli
how the eye functions to produce a focused image
light rays from an object enter the transparent cornea
cornea bends to refract light rays towards one another
light ray passes through pupil
elastic lens is altered in shape
brings rays to focus on retina
cells are stimulated by the light of the image and convert light energy into electrical energy
electrical in form of impulse travels along the optic nerve to the brain
brain decodes the impulses to produce sight
what is the iris
muscular structure that controls how much light passes through the pupil
what is yellow spot/ fovea
the most sensitive part of the retina on which objects in the centre of the field of vision are focused is called the yellow spot or fovea
what happens when people are colour blind
deficient usually in red and green cones
why are rod cells more effective in dim light
rod cells are more light sensitive than cone cells
cone cells responsible for
each type of cone cell is sensitive to one type of light. red green and blue
why do we have a blind spot
because there are no rods or cones where the retina is joined to the optic nerve. images formed on this part of the retina are not relayed to the brain. this region is therefore called the blindspot. dont notice this because one eye can cover for the over
what is accommodation
the ability to change the focal length of the lens so that er can see both near and far objects
what does accommodation rely on
elasticity of the lens
existence of the ciliary muscles, which are used to alter the shape of the lens
the suspensory ligaments, which transfer the effect of the ciliary muscles to the lens
pupil or iris reflex
the reflex is described as the iris reflex.
how do the iris muscles work to control pupil size
the iris has an antagonistic arrangement of circular and radial muscles.
in bright light
light sensitive cells in the retina detect the light intensity
impulses sent along the optic nerve to the brain
brain returns impulses along a motor nerve to the circular muscles of the iris
the circular iris muscles contract whilst the radial iris muscles relax
the diameter of the pupil decreases allowing less light to decrease damage to the retina.
cornea
refracts light - bends it as it enters the eye
iris
controls how much light enters the pupil
lens
focuses light on to the retina
retina
contains light receptors
rods
sensitive to dim light and black and white
cones
sensitive to colour
optic nerve
carries impulses from the eye to the brain.
where has the most of the cones and rods
fovea in the middle of the retina
why is the light refracted by the eye
refracted by the cornea and lens so the light can focus of the lens
what is Stereoscopic vision
each eye captures a slightly different view and when signals from both eyes reach the brain they are superimposed and produces into one picture with depth
from this we can form 3D pictures and can judge distances well.
short-sight
can see near objects clearly but not far away.This is because the lens focuses the sharpest image in front of the retina, instead of on it.
long-sight
Someone with long-sightedness can see distant objects clearly, but cannot focus properly on near objects. This is because the lens focuses the sharpest image behind the retina, instead of on it.
how can short-sightedness be fixed?
This is caused by the eyeball being elongated, so that the distance between the lens and the retina is too great. It can be corrected by placing a concave lens in front of the eye.
how can long-sightedness be fixed?
This is because the lens focuses the sharpest image behind the retina, instead of on it. This defect is often age-related, and due to a loss of elasticity in the lens. It is corrected by putting a convex lens in front of the eye.
