B3.1.3 The Eye Flashcards
Cornea
Transparent coating on front of eye which protects the eye and refracts light entering it
Pupil
The central hole in the iris which allows light to enter eye
Iris
A coloured rind of muscle tissue which alters pupil size by contracting or relaxing
Lens
Transparent biconvex lens which focuses light clearly onto retina
Ciliary body
Ring of muscle tissue which alters shape of lens in order to focus on objects far and near
- contract=lens convex (fatter), focus on nearby objects
- relax=lens less convex (thinner), focus on distant objects
Suspensory ligaments
Ligament tissue which connects the ciliary muscle to the lens
Optic nerve
Nervous tissue which carries nerve impulses to the brain
How are images formed
Cornea refracts incoming rays of light, providing focus. Light then passes through pupil, further refracted by lens creating sharp image onto retina. Photoreceptors in retina produce nervous impulse when exposed to light which travels down optic nerve to brain which interprets impulse as visual image.
What is short sightedness caused by?
Lens is too strong OR eyeball too long
What is long sightedness caused by?
Lens too weak OR eyeball too short
How to fix shortsightedness
Concave lens-bends light rays outwards
How to fix longsightedness
Convex lens-bends light inwards
Photoreceptors
Light sensitive cells in retina which produce nervous impulse when exposed to light
2 types of photoreceptor cells
Rods-respond to light, allowing you to see in low light levels
Cones-respond to different colours (red, blue, green light)
What is colour blindness?
Difficulty making out different colours/not seeing colours
- genetically inherited
- more common in males
- most common is red-green (not distinguishing between 2)
