Results in the formation of a blur circle around a highly focused centre on the retina

Is the differential focusing of horizontal and vertical light rays from the same object on to different retinal points

Arises because of an increase in the length of the eyeball

Arises because of an decrease in the length of the eyeball

Arises because of a mis-match between the refractive indices of the cornea and the lens

parafovea

sclera

choroid

the fovea

optic disk

low levels of cyclic GMP result in sodium channel closure

high levels of cyclic GMP result in sodium channel closure

low levels of cyclic GMP hold the sodium channels open

high levels of cyclic GMP hold the sodium channels open

centimetres

millimetres

radioptres

metres

dioptres

iris

ampulla

retina

choroid

vitreous humor 

fovea 

sclera

retina

cornea

choroid

pupil

iris

lens

retina

cornea

To control the action of guanylate cyclase for light adaptation

To trigger the activation of the G protein sequence in phototransduction

To amplify the standing current flow in rods

To keep open the ion channels that allow influx of Na⁺ and Ca⁺⁺

To keep open the ion channels that allow influx of Na⁺ and efflux of K⁺