lecture 3- light and the eye

Question 1

how is light measured?

Answer 1

wavelengths

Question 2

how can we not see infrared rays but feel them?

Answer 2

as heat - certain types of snake can see heat and so can better attack their prey

Question 3

how are images formed from reflected visible light?

Answer 3

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

Question 4

what are the issues with camera obscuring?

Answer 4

trade off between the lightness and the sharpness

Question 5

how do we focus an image on the back of our eye?

Answer 5

lens in the human eye - creates a sharp image on the back of our eye

Question 6

what is in the human eye?

Answer 6

cornea - transparent tissue at the very front of the eye.
Sclera – Tough white tissue that coats the rest of the eye
iris

Question 7

what are the optical components?

Answer 7

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.

Question 8

what is presbyopia?

Answer 8

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.

Question 9

what is hyperopia?

Answer 9

farsightedness

Question 10

what is myopia?

Answer 10

Structural diffs in shape of eye or lens - bends too much light and brings the focal point infront of the retina

Question 11

what are the cells of the eye?

Answer 11

rods, cones and visual neurons

Question 12

what is the anatomy of rods and cones?

Answer 12

outer segments, inner segments and synaptic terminal

Question 13

what is the transduction of light into nerve impulses?

Answer 13

visual pigment molecules, opsin, retinal - isomerisation - changes shape

Question 14

what are cones?

Answer 14

Small and numerous in the fovea
Larger but fewer in the periphery
Contribute to day-time spatial, high acuity vision
Responsible for colour vision

Question 15

what are rods?

Answer 15

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

Question 16

what is dark adaptation?

Answer 16

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

Question 17

what is dark adaptation?

Answer 17

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

Question 18

what are retinal cell layers?

Answer 18

R – Receptors (Rods and Cones)
H - Horizontal cells
B - Bipolar cells
A - Amacrine cells
G - Ganglion cells

Question 19

why are rods more sensitive to light than cones?

Answer 19

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

Question 20

why do cones provide more visual acuity?

Answer 20

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