the eye

• pupil - opens and closes to regulate the amount of light entering the eye
• iris - controls the amount of light entering the eye
• sclera - protective outer coat
• cornea - refracts light rays onto the retina and provides 67% of the eye's focusing power
• conjunctiva - covers and protects the cornea
• aqueous humour - maintains the shape of the cornea
• vitreous humour - maintains the shape of the eyeball
• retina - contains light-sensitive cells called rods and cones. captures the light rays focused by the lens and sends impulses to the brain via optic nerve and an image forms
• optic nerve - carries impulses from the retina to the brain
• ciliary muscles - contracts and extends in order to change the lens shape for focusing
• Lens - transparent, elastic, biconvex structure. Makes fine adjustments to focus light rays on the retina
• suspensory ligament - attaches the lens to the ciliary body
• blind spot - point where the optic nerve leaves the eye. no light-sensitive cells are present
• choroid - contains blood vessels which supply the retina with food and oxygen and melanin to prevent reflection of light inside the eye
• fovea - contains cones only. most sensitive part of the retina as most light rays are focused there
• Light entering the eye from a near object needs a lot of bending(inwards) and so a thicker (bulge or be more curved) lens is needed.The ciliary muscles contract causing the suspensory ligament toslacken. This results in a thicker lens.
• Looking at far objects - The ciliary muscles relaxes causing the suspensory ligament to tighten. This results in a thinner lens.
• the retina is composed of two types of specialised light-sensitive cells or photoreceptors
• The rods function in dim light because in bright light the pigment in therods, rhodopsin is bleached or is broken down. They are responsible for detecting the brightness of light and are located around the sides of the retina. Images falling on the rods are seen in shades of black and white
• The cones detect colour and work best in bright light and sends thisinformation to the brain. The pigment in the cones, iodopsin does notbreak down in bright light like rhodopsin. The cones also detect finedetails and so the fovea is composed of only cones. There are three types that detect either red green or blue wavelengths of light. They are located at the back of the retina.
• short sight is myopia
• long sight is hypermetropia
• glaucoma is a condition in which the pressure of the fluid within the eye increases due to the flow of aqueous humour from the eye being blocked.
• If glaucoma is left untreated, the optic nerve will become damaged, leading to blindness
• the eye detects light that has been reflected from an object and converts it into nerve impulses
• the nerve impulses are transmitted along the optic nerve to the brain which translates them into a precise picture of the object.
• the eyes are situated in bony sockets of the skull called orbits that have muscles attached to move them
• tears help to keep the eye moist and wash away foreign particles and contain an enzyme that destroys micro-organisms