Physioptics

Question 1

emmetropia

Answer 1

light brought to focus on the retina

Question 2

hyperopia

Answer 2

far sightedness, eye too short/lens too weak

Question 3

myopia

Answer 3

near sightedness, eye too long/lens too strong

Question 4

presbyopia

Answer 4

hardening of lens - muscles cant change the shape of the lens, can’t thicken to focus on near objects

Question 5

astigmatism

Answer 5

eye does not focus light evenly on the retina - distorted/blurred vision

Question 6

neural types in retina (3)

Answer 6

photoreceptor cells (outer nuclear layer), bipolar cells (inner nuclear layer) and retinal ganglion cells (retinal ganglion cell layer)

Question 7

Rod Structure

Answer 7

Outer segment - cylindrical shape, membrane pinched off to form stack of intracellular discs

Question 8

Cone Structure

Answer 8

Outer segment - contains multiple invaginations - form discs continuous with the outer membrane of the cell

Question 9

Foster Et al 1991

Answer 9

non cone non rod photoreceptors, intrinsically photoreceptive retinal ganglion cells - when take out rods and cones from mice still respond to light, contain melanopsin, absorption peak 480nm, different to both rods and cones

Question 10

rhodopsin structure

Answer 10

protein moeity called opsin covalently bonded to cofactor retinal

Question 11

Phototransduction (9)

Answer 11

1. darkness - photoreceptor membrane potential is -40mV, cyclic nucleotide gated channels are open and there is a dark current due to the influx of Na+ and Ca2+
2. retinal cofactor absorbs photon - photoisomerism, conformational change in shape from 11-cis isomer to all-trans retinal
3. triggers change in opsin molecule - metarhodopsin II
4. diffuses through membrane of cell until comes into contact with transducin
5. exchanges a GDP for a GTP
6. Talpha-GTP (active subunit) - then joins cyclic nucleotide phosphodiesterase
7. enzyme hydrolyses cGMP to 5’GMP at a faster rate
8. decrease in cGMP leads to closure of cyclic nucleotide gated channels
9. dark current ceases, cell is hyperpolarised, gluatamate release ceases

Question 12

ON Bipolar Cell

Answer 12

metabotropic receptor (mGluR6) - responds to glutamate by closing channels and hyperpolarisation

Question 13

OFF Bipolar Cell

Answer 13

ionotropic receptor - glutamate leads to signalling and depolarisation

Question 14

Fovea (3)

Answer 14

1.5mm accross, central foveolar (0.5 mm across)

retinal nerve bodies are shifted aside from the central fovea so light has a more direct path to photoreceptors

Question 15

Deutranomaly

Answer 15

abnormal middle wavelength pigment

Question 16

protanomaly

Answer 16

abnormal long wavelength pigment

Question 17

protanopia

Answer 17

missing long wavelength pigment

Question 18

deutranopia

Answer 18

missing long wavelength pigment