W2 - The Eye And The Retina ✅

Question 1

What is meant by retinal image (how can we see?)

Answer 1

Object (distal stimulus) reflects light to the eye and to retina (proximal stimulus)

Light affects the colour and brightness of image

Question 2

Describe the main structure of the eye?

Answer 2

1. Pupil: the opening to let light in
2. Cornea: focus light
3. Iris: control diameter of pupil - amount of light
4. Len: focus light by changing shape (distance)
5. Retina: make up of photoreceptors (receive light to form inverted image of object) -> full/clearest focus at fovea

Question 3

How can the lens change to accompany the distance between object to eye?

Answer 3

• Contract (fatter) for closer object -> light refracted more
• Relax (thinner) for further object -> light refracted less almost parallel

Refraction errors:
1. Nearsighted - myopia
2. Farsighted - hyperopia

Question 4

What are the two types of photoreceptors and their functions?

Answer 4

1. Rod:
   - 120 millions
   - Very sensitive
   - Useless in daylight (identify contrast)
2. Cone:
   - 6 millions
   - Less senstive
   - Useless at night

-> Differ in: number, light sensitivity, retinal distribution, neural convergence and acuity

Question 5

What are the different regions of vision?

Answer 5

1. Scotopic: rods active (B&W vision)
2. Photopic: cones active (colour & no light intensity)
3. Mesopic: both active (normal vision)

Question 6

Explain adaptation to darkness using cones and rods?

Answer 6

1. Why we can’t see in the dark initially: bright light bleaches photopigments -> stop responding (mainly rods)
2. Adaptation: dark - rods become active so sensitivity increases (B&W image)

Question 7

Explain colour perception using cones and rods

Answer 7

• Cones are sensitive to different wavelengths of light -> perceive colours
• 3 types:
  1. Red (long)
  2. Green (med)
  3. Blue short
• Rods can only offer monochromatic vision and are most sensitive to green (med wavelength)

Question 8

What is the retinal distribution of cones and rods?

Answer 8

1. Most areas: predominantly rods
2. Foves: only cones - central area which most images fall here
3. Blind spot: no rod & cone (connector of neuron)

Question 9

Explain neural convergence & acuity of rods and cones?

Answer 9

Convergence rate to ganglion cells
- Rods: 126:1
- Cones: 6:1

More convergence -> lower acuity (ability to detect fine details)