describe the differences in distribution, structure and function of the photoreceptor cells in the human eye Distribution, structure + function of photoreceptor cells – Feature Rod cells Cone cells 125 million 7 million Number (per human eye) Cover retina (most Most concentrated in fovea Distribution concentrated on periphery) (central retina) EXCEPT fovea Rod-shaped end Cone-shaped end Structure stacked with stacked with membrane membrane layers layers containing containing photopigments photopigments Work best in low light Work best in bright light Function levels (allow good night vision) Detect colour Do not detect colour Provide ability (monochromatic) visual acuity – Detect shape + movement to see objects sharply + clearly NOTE: used to Snellen chart – assess visual acuity (stand certain distance from eye chart to determine smallest line of print they can read) NOTE: nocturnal (active during night) animals, have higher % of rod cells e.g. cat, since rods work well in low light settings cats hunt for prey at night – NOTE: diurnal (active during day) animals, have higher % of cone e.g. pigeon,
describe the differences in distribution, structure and function of the photoreceptor cells in the human eye Distribution, structure + function of photoreceptor cells – Feature Rod cells Cone cells Number (per human eye) 125 million 7 million Distribution Cover retina (most concentrated on periphery) EXCEPT fovea Most concentrated in fovea (central retina) Structure Rod-shaped end stacked with membrane layers containing photopigments Cone-shaped end stacked with membrane layers containing photopigments Function Work best in low light levels (allow good night vision) Do not detect colour (monochromatic) Detect shape + movement Work best in bright light Detect colour Provide visual acuity – ability to see objects sharply + clearly NOTE: Snellen chart – used to assess visual acuity (stand certain distance from eye chart to determine smallest line of print they can read) NOTE: nocturnal (active during night) animals, e.g. cat, have higher % of rod cells since rods work well in low light settings – cats hunt for prey at night NOTE: diurnal (active during day) animals, e.g. pigeon, have higher % of cone