Week 2

Question 1

what is light

Answer 1

a wave

Question 2

how to convert electromagnetic energy into visual perception

Answer 2

1. focus light
2. capture and signal presence of light
3. provide neural processinf for image extraction

Question 3

how to capture and signal presence of light

Answer 3

filtering and transduction
dark and light adaption

Question 4

what limits light reaching the photoreceptors

Answer 4

-5% is lost through reflection at optical interfaces
-Pupil limits the amount of light passing through
% transmitted light depends on the optical density of the media
% transmitted depends on spectral absorption of intervening tissue

Question 5

how is retinal illuminance calculated

Answer 5

proportional to the square of the pupil radius

Question 6

how to calculate transmission

Answer 6

T=10-d

to the power of minus d

Question 7

Features of the cornea

Answer 7

absorbs very short wavelengths
excessive UV exposure can lead to photokeratitis

Question 8

features of the lens

Answer 8

The greatest source of protection from the retina
Scatters 16x more blue light than red
Beta and something crytsallins absorb short wavelength radiation

Question 9

features of lens pigmentation

Answer 9

Increases in diabetes mellitus
Nuclear cataracts

Question 10

features of macular pigment

Answer 10

Macular lutea – central retinal region containing inner-retinal non-photosensitive yellow pigment
Pigment comprises two carotenoid pigments = lutein and zeaxanthin
Absorbtion peak at 460nm

Question 11

What is the function of pre-receptor absorption?

Answer 11

Protects the photoreceptors from light damage
Limits the possibility of chromatic aberration
Minimizing scatter, minimizes noises in visual discrimination tasks

Question 12

why is the retinal pigment epithelium dark

Answer 12

Light is absorbed by the PE if it passes through the retina without being absorbed

Question 13

What are the segments of a photoreceptor

in the light

Answer 13

Outer segment filled with stacks of membranes containing visual pigment molecules sch as rhodopsin or iodopsin

Inner segment containing mitochondria, ribosomes and membranes where opsin molecules are assembled and passed to be part of outer segment discs

A cell body containing nucleus of photoreceptor cell

Synaptic terminal where neurotransmission to second-order neurons occurs

Question 14

how do the segments of a photoreceptor work in the dark

Answer 14

Outer segment channels are open + flow of NA+ into the receptor (dark current)

Neurotransmitter (glutamate) is being constantly releases from synapse to the next neuron

Photoreceptor is in slightly depolarized state

Question 15

what are the 2 main parts to a pigment molecule

Answer 15

Opsin – a long chain of 364 amino acids
Chromophore – consists of chemical called retinal – vitamin A within membrane

Question 16

how do the segments of a photoreceptor work in the light

Answer 16

Isomerization of 11-cis retinal to all-trans retinal / shape straightens out
No longer binds to the opsin and it is expelled
Causes closure of ion channels of the rod / cell hyperpolarization
Purple pigment (sehpurpur) changed to yellow to clear when exposed to light revelealing

Question 17

what is transduction

Answer 17

Purple pigment (sehpurpur) changed to yellow to clear when exposed to light revelealing process of transduction

Question 18

problems with transduction process

Answer 18

Defects within signalling system of photoreceptors leads to retinal dystrophy

Retinal dystrophy

Question 19

which cones are identical

Answer 19

96% identical red and green

Question 20

What is the spectral luminosity function?

Answer 20

Describes visual sensitivity as a function of wavelength

Question 21

Photopic spectral sensitivity function

Answer 21

describes human sensitivity under photopic conditions

black and white

Question 22

scotopic spectral sensitivity function

Answer 22

describes sensitivity under scotopic conditions