eye

• sclera - tough, supporting the wall of the eye
• cornea - transparent outer layer, refracts light into the eye
• iris - contains muscles to control the diameter of the pupil and how much light enters the eye
• lens - focuses the light onto the retina (contains receptor cells sensitive to light intensity and colour)
• shape of lens controlled by ciliary muscles and suspensory ligaments
• optic nerve - carries impulses from the receptors on the retina to the brain
• when light is visible, light receptors detect that bright light so a reflex is triggered that makes the pupil smaller - circular muscles contract and radial muscles relax - reduces amount of light to enter the eye
• when there's dim light, light receptors detect the dim light so a reflex is triggered that makes the pupils larger - radial muscles contraxt and circular muscles relax - allows more light to enter the light
• hyperopia - long sighted - when the lens doesnt refract light enough / eyeball is too short
• myopia - short sighted - lens refracts the light too much / eyeball is too long
• treatments for vision defects: contact lenses, laser eye sugery, replacement lens surgery
• contact lenses - thin lenses that sit on the surface of the eye and shaped to compensate the fault in focusing
• laser eye surgery - vaporises tissue, changing the shape of the cornea (changes how strongly it refracts light into the eye)
• replacement lens surgery - natural lens of the eye is removed and an artificial lens is inserted in its place