lecture 3- light and the eye Flashcards
how is light measured?
wavelengths
how can we not see infrared rays but feel them?
as heat - certain types of snake can see heat and so can better attack their prey
how are images formed from reflected visible light?
camera obscura - Shine light through a tiny hole in a dark room to see an inverted image of statue - as the light has been reflected off it
what are the issues with camera obscuring?
trade off between the lightness and the sharpness
how do we focus an image on the back of our eye?
lens in the human eye - creates a sharp image on the back of our eye
what is in the human eye?
cornea - transparent tissue at the very front of the eye.
Sclera – Tough white tissue that coats the rest of the eye
iris
what are the optical components?
cornea
lens - Adjusts shape according to object distance
Ciliary muscles – increase focusing power of lens by increasing its curvature
Accommodation – Ciliary muscles tighten causing lens to thicken and focus on close objects.
what is presbyopia?
Hardening of lens and weakening of ciliary muscles causes distance of near point to increase with age.
Corrective lenses are needed for close activities, such as reading.
what is hyperopia?
farsightedness
what is myopia?
Structural diffs in shape of eye or lens - bends too much light and brings the focal point infront of the retina
what are the cells of the eye?
rods, cones and visual neurons
what is the anatomy of rods and cones?
outer segments, inner segments and synaptic terminal
what is the transduction of light into nerve impulses?
visual pigment molecules, opsin, retinal - isomerisation - changes shape
what are cones?
Small and numerous in the fovea
Larger but fewer in the periphery
Contribute to day-time spatial, high acuity vision
Responsible for colour vision
what are rods?
Absent in fovea
Far more numerous than cones in peripheral retina
More sensitive in low light and therefore responsible for night vision
Have little role in colour vision – why colours are less apparent in dim light
what is dark adaptation?
Process of increasing sensitivity to light in the dark
Measured by a dark adaptation curve
rods are more sensitive in low levels of light
When go from light to darkness initially v difficult to see and cant make our details in room then our vision adapts to the light and we can see certain light and objects
what is dark adaptation?
Light-adapted sensitivity is measured by establishing the threshold for seeing the test light while in a lit room
The light in the room is turned off and the participant must adjust the intensity of to keep it barely visible as their eyes adapt to the dark
Test light is focused onto either rods or cones
what are retinal cell layers?
R – Receptors (Rods and Cones)
H - Horizontal cells
B - Bipolar cells
A - Amacrine cells
G - Ganglion cells
why are rods more sensitive to light than cones?
Individually, rods require less light to respond
Convergence of rod activity on bipolar/ganglion cells increases likelihood of neural firing
Convergent rod pathways cannot resolve fine detail
why do cones provide more visual acuity?
All-cone foveal vision involves one-to-one wiring with ganglion cells
Provides information to brain about spatial position of light stimulus leading to ability to discriminate fine detail
Cones need far more light to cause response in ganglion cells than rods
