Lecture 3 Eye/Retina

Question 1

TRUE or FALSE: gamma rays are short and radio waves are long

Answer 1

true

Question 2

What is the range of the visible spectrum for humans?

Answer 2

400 to 700 nm

Question 3

light enters the eye through the _______ and is focused by the _______ and the ________ to a sharp image on the _________.

Answer 3

pupil, cornea, lens, retina

Question 4

What are the visual receptors in the retina called?

Answer 4

rods and cones

Question 5

How many rods and cones are in the human eye?

Answer 5

120M rods, 6M cones

Question 6

shape of rods and cones?

Answer 6

rods are large and cylindrical; cone are small and tapered

Question 7

what is destroyed first in macular degeneration? What aspect of vision does it affect? Who is it most common in?

Answer 7

fovea and small surrounding area are destroyed; high acuity vision; older individuals

Question 8

What is destroyed first in retinitis pigmentosa? What aspect of vision does it affect? What can also be destroyed? What is its main cause?

Answer 8

rods are destroyed first; night vision; FOVEAL cones; genetic

Question 9

Why don’t we notice the blind spot?

Answer 9

• one eye covers the blind spot of the other
• it is located towards the edge of our visual field
• brain fills in missing information by extrapolating what’s around it (top-down processing)

Question 10

The _________, which is fixed, accounts for about 80% of the focusing power of our eye

Answer 10

cornea

Question 11

The __________, which adjusts shape for object distance, accounts 20% of the focusing power of our eye

Answer 11

lens

Question 12

TRUE or FALSE: we can see near objects clearly when our lenses are relaxed

Answer 12

FALSE: far away objects

Question 13

_____________ occurs when ciliary muscles are tightened.

Answer 13

accommodation

Question 14

TRUE or FALSE: the lens thickens during accommodation

Answer 14

TRUE

Question 15

Explain accommodation.

Answer 15

1. ciliary muscles tighten
2. lens thickens
3. lens focus light rays
4. near objects focused on retina

Question 16

Myopia occurs when the image gets focused _____________ the retina.

Answer 16

in front of

Question 17

refractive myopia vs axial myopia

Answer 17

• refractive myopia: cornea or lens bends too much light
• axial myopia: eyeball is too long

Question 18

hyperopia occurs when the image gets focused ___________ the retina.

Answer 18

behind

Question 19

What is also known as old eye?

Answer 19

presbyopia

Question 20

Presbyopia occurs when the lens _________________________ .

Answer 20

can no longer adjust for close objects

Question 21

What is presbyopia caused by?

Answer 21

hardening of lens and weakening of ciliary muscles

Question 22

TRUE or FALSE: opsin is a light sensitive molecule.

Answer 22

FALSE: retinal

Question 23

What is visual transduction?

Answer 23

occurs when the retinal absorbs one photon, causing it to change shape (isomerization)

Question 24

What is dark adaptation?

Answer 24

process of increasing visual sensitivity after switching from high to low-level lighting conditions

Question 25

What are the steps to determining the dark adaptation curve?

Answer 25

1. observer starts in lit room and becomes 'light adapted' 2. lights turned off, observer adjusts intensity of a test light until it is just barely visible (determines their sensitivity at the beginning of the curve) 3. as time passes, they continue to readjust intensity of the test light

Question 26

How do you measure cone vs. rod vs. both for sensitivity in dark adaptation?

Answer 26

- cone: participant looks directly at light - rod: participant must be rod monochromat - both: participant fixates on point while light is shined from the side

Question 27

How long does stage one of the dark adaptation curve take place for?

Answer 27

3-4 mins

Question 28

How long does the rod-cone break of the dark adaptation curve last for?

Answer 28

7-10 mins

Question 29

How long does stage 2 of the dark adapation curve last for?

Answer 29

20-30 mins

Question 30

What is the process needed for transduction?

Answer 30

- retinal changes shape - opsin separates - retina shows visual pigment bleaching - retinal and opsin recombine during REGENERATION (to respond to light again)

Question 31

TRUE or FALSE: as our vision improves in the dark, visual pigments regenerate at a slower rate than they are being used

Answer 31

FALSE: faster rate

Question 32

What is spectral sensitivity?

Answer 32

sensitivity of rods and cones to different parts of the visible spectrum

Question 33

___________________ light can be used to determine threshold at different wavelengths, for spectral sensitivity.

Answer 33

monochromatic

Question 34

TRUE or FALSE: threshold is the same as sensitivity

Answer 34

FALSE: threshold is the reciprocal of sensitivity

Question 35

Draw the spectral sensitivity curve vs the threshold curve.

Answer 35

spectral peak is up, threshold peak is down

Question 36

Which colour/part of the visible spectrum are humans most sensitive to? is this where the lowest or highest threshold is?

Answer 36

- greenish/yellow (middle) - lowest threshold (for highest sensitivity)

Question 37

TRUE or FALSE: rods are more sensitive to short-wavelength light.

Answer 37

TRUE

Question 38

At what wavelength are rods and cones most sensitive?

Answer 38

- rods at 500 nm - cones at 560 nm

Question 39

What is the Purkinje shift? Provide an example.

Answer 39

- enhanced sensitivity to short wavelengths during dark adaptation when the shift from cone to rod vision occurs - blue seems brighter to a dark-adapted eye vs light-adapted eye

Question 40

At which 3 wavelengths do cone pigments absorb best?

Answer 40

419 nm, 531 nm, 558 nm

Question 41

rods and cones send signals vertically through which cells?

Answer 41

bipolar and ganglion

Question 42

rods and cones send signals horizontally through which cells?

Answer 42

horizontal and amacrine

Question 43

There is higher convergence in __________ than ________.

Answer 43

rods, cones

Question 44

Describe the convergence of rods vs cones to ganglion cells.

Answer 44

- 120 rods: 1 ganglion cell - 6 cones: 1 ganglion cell

Question 45

TRUE or FALSE: cones in the periphery have a one to one relation to ganglion cells

Answer 45

FALSE: cones in the fovea

Question 46

TRUE or FALSE: more convergence of rods = less sensitive

Answer 46

FALSE: more sensitive

Question 47

TRUE or FALSE: less convergence of cones = lower acuity

Answer 47

FALSE: better acuity