The Eye Flashcards
Cornea
A curved transparent disc at the front of the eye. Does most of the focusing
Pupil
A circular opening whose size is controlled by the iris
Iris
A ring of muscles with a hole in the middle (pupil). The iris controls how much light enters the eye
Lens
This is soft, flexible and transparent. Its shape can be changed to fine tune the focusing of light onto the retina
Ciliary muscles
A ring of muscle at the edge of the eye which circles the lens. When it contracts the lens gets fatter. When it relaxes the lens gets thinner
Suspensory ligaments
Strong fibres which attach the lens to the ciliary muscle
Retina
Contains light sensitive cells called rods and cones
Optic Nerve
Consists of many neurones which carry impulses from the retina to the brain
Fovea
The region of the retina with the most rods and cones
Conjunctiva
A mucous membrane that covers the eye to prevent infection
What happens when the eye is exposed to dim light?
Radial muscles contract
Circular muscles relax
This makes the iris narrower
Therefore pupil dilates (gets bigger)
What happens when the eye is exposed to bright light?
Circular muscles contract
Radial muscles relax
This makes the iris wider
Therefore pupil constricts (gets smaller)
What happens when the eye focuses on an object which is far away?
Ciliary muscles relax
Therefore suspensory ligaments are pulled tight
Lens is pulled thin and has less convex shape
Therefore less refraction of light
What happens when the eye focuses on an object which is close?
Ciliary muscles contract
Therefore suspensory ligaments are slack
Lens is not stretched out so it becomes thicker and more convex
Therefore more refraction of light
