• Cornea refracts light through the pupil & lens• Lens may change shape for objects at distance• Image is projected INVERTED on the retina• Each eye has a blind spot where the optic nerve & blood vessels enter the eye.
Retina • A thin layer on the back of the eye where light is converted to an electrical signal and passed through the optic nerve to the eye.
• Photoreceptors called RODS & CONES sense light• RODS: great at low light sensing, poor resolution & colour• CONES: functions only in bright light & provides information about colour & detail
CONES are responsible for our colour vision isknown as TRI-CHROMATIC visionWe see as a combination of 3 colours:RED (630 nm) BLUE (420 nm) GREEN (560 nm)Rods absorb light best at 540 nmEach cone cell contains pigment moleculesdesigned to absorb different wavelengths of light
Visual Pigments • Each pigment is composed of two molecules: – OPSIN • Proteins that react to specific wavelengths of light • All rods contain a specific type – CHROMOPHORE • RETINAL – a modified form of Vitamin A which changes shape in response to light
Different firing rates ofphotoreceptor cellsare sent to the brainwhere the rates arecompared.The optic nerves crossat the OPTIC CHIASMand each eye’s signal issent to the occipitallobe of the brainwhere the image is‘assembled’.