The Human Eye
Photoreceptors in the retina
External and Internal Structure of the Eye
connected to nerve endings from the optic nerve
Rods and cones are photoreceptors
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Cones
Rods
enables us to see colours in bright light
three types of cones: red, blue & green cones
do not work well in dim light
enable us to see in dim light in black & white
sensitive to light of low intensity because they contain a pigment called visual purple
when the eye is exposed to bright light, all the visual purple is bleached
upon movement from a brightly-lit room to a dimly-lit room, visual purple needs to be formed again and it takes some time
formation of visual purple requires Vitamin A.
a person deficient in Vitamin A maybe unable to see in dim light & is said to suffer from night blindness.
Pupil Reflex
controls the amount of light entering the eye
by altering the diameter of the pupil
Size of pupil is controlled by 2 involuntary muscles in iris; radial & circular muscles
stimulus -> receptor (retina) -> sensory neuron in optic nerve -> brain -> motor neuron -> effector (iris)
Characteristics of image formed in the eye
Accommodation
inverted
laterally inverted
diminished
adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina