The EYE

Layers of the Eye Sclera Choroid layer Retina

Sclera Thick, white outer layer gives the eye its shape Cornea ◦Front of the sclera – buldges and becomes clear Conjunctiva ◦Thin membrane that covers the cornea ◦Kept moist by tears

Choroid Layer Middle layer Coloured to absorb light (prevents internal refraction) Front becomes the IRIS ◦Opens & closes to control size of pupil Cilary Body ◦Muscles that control the LENS

Retina Inner layer Two types of photoreceptors ◦Rods ◦Cones

Rods More sensitive to light Unable to distinguish colour Shades of grey Ideal for night vision Many rods can attach to one bipolar cell Retina contains 150 million

Cones Require more light to stimulate them Able to detect red, blue and green Each cone connects to one bipolar cell ◦Gives detailed image Retina contains 6 billion

Anterior Chamber Between the cornea and the lens Filled with fluid called aqueous humour Pre lens ◦Initiates focusing of an image on the retina before it reaches the lens Lens ◦completes focusing

Posterior Chamber Filled with a clear gel called vitreous humour Helps the eye keep its shape

How we see….. Light enters the eye Pupil adjusts ◦Pupil also constricts when you focus on something close to reduce distortion Shape of lens changes ◦Far – ciliary muscles relax  Suspensory ligaments get tight  Lens flattens ◦Near – cilary muscles contract  Suspensory ligaments less tension  Lens becomes more rounded ◦ Accommodation

Image is focused on retina ◦Bipolar cells synapse with rods and cones and transmit impulses to ganglion cells ◦Ganglion cells join together to form the optic nerve Message is sent to occipital lobe in the brain