Lecture 18

Question 1

What is radiant energy described by?

Answer 1

Wavelength and Frequency

Question 2

What is Wavelength?

Answer 2

The distance between two successive wave peaks

Question 3

What is Frequency?

Answer 3

The number of cycles per second

Question 4

Name the 2 basic components of the Eye

Answer 4

1) Optical Component
2) Neural Component

Question 5

What is the function of the Optical Component?

Answer 5

• Collects light
• Focus light onto the retina

Question 6

What is the function of the Neural Component?

Answer 6

Phototransduction
- Light → change in membrane potential
Conduct action potentials to parts of the brain that decode the electrical signals to generate visual perceptions

Question 7

What is Refraction and what is the function?

Answer 7

• Bending of light waves
• Allows accurate image of objects to be focused onto retina

Question 8

When does Refraction occur?

Answer 8

When light passes between different media with different refractive indices

Question 9

What is the Refractive Index?

Answer 9

The angle of light bending
- Also related to the curvature of the refractive surface
- Refraction by lens changes as it changes shape

Question 10

What are the conditions necessary for viewing distant objects?

Answer 10

• Ciliary muscle is relaxed
• Zonular fibres are stretched
• Lens is flattened

Question 11

What are the conditions necessary for viewing close objects?

Answer 11

• Increased parasympathetic signalling to ciliary muscle
• Ciliary muscle contracts
• Tension removed from zonular fibres
• Lens becomes more spherical
• Eye’s refractive power increases

Question 12

What is the parameter for unaccommodated vision?

Answer 12

Low ≈ 60 diopters

Question 13

What is the parameter for fully accommodated vision?

Answer 13

High ≈ 75 diopters

Question 14

What happens with age?

Answer 14

Lens loses elasticity = less accommodation for near vision = reading glasses for presbyopia

Question 15

What 3 processes occur as you shift your gaze from distant to near objects?

Answer 15

1) Accommodation
2) Constriction of pupil
3) Convergence of eyes

Question 16

Describe the process of Accomodation

Answer 16

• Contraction of ciliary muscle
• Lens becomes more rounded
• Increased refraction

Question 17

Describe the process of Constriction of Pupil

Answer 17

• Improved depth of focus
• Fewer optical aberrations

Question 18

Describe the process of Convergence of eyes

Answer 18

Aim to keep object’s refracted light on fovea

Question 19

What does the Retina contain?

Answer 19

Photoreceptors = light sensitive cells
- Furthest from incoming light

Question 20

How does the information flow through the Retina?

Answer 20

Flows between photoreceptors and ganglion cells via interneurons

Question 21

What is the function of the Ganglion cells in the Retina?

Answer 21

Send information, through axons that become the optic nerve, to brain for further processing

Question 22

Define Phototransduction

Answer 22

Conversion of light energy into a change in membrane potential

Question 23

What is in the Outer segment of the Retina?

Answer 23

Machinery to respond to light
- Stacked layers of membrane called disks

Question 24

What is in the Inner segment of the Retina?

Answer 24

Cell organelles and synaptic terminal

Question 25

Describe the features of the Cones

Answer 25

- 8 million per retina - Many in fovea - Require relatively high light levels (day & twilight vision) - 3 types, sensitive to red, green, blue light

Question 26

Describe the features of the Rods

Answer 26

- 120 million per retina - Few in fovea - Function in low light (night vision) - Do not report information about colour

Question 26

What do Photoreceptors contain?

Answer 26

Photopigments - Transmembrane proteins called Opsins

Question 27

What do Rods contain?

Answer 27

Rhodopsin (Do not detect colour)

Question 28

What are the 3 types of Photopsin that Cones contain?

Answer 28

S-photopsin - Short Wavelengths (blue) M-photopsin - Medium Wavelengths (green) L-photopsin - Long Wavelengths (red)

Question 29

What happens in dark conditions?

Answer 29

- Na+ ion channels are open (depolarises the cell) - RMP in photoreceptor ≈ -40 mV - Neurotransmitter being released onto bipolar cells

Question 30

What are the Retinal ganglion cell axons projections to the 4 subcortical visual areas?

Answer 30

1) Suprachiasmatic Nucleus (hypothalamus) - Controls diurnal/circadian rhythms 2) Pretectum (brainstem) - Reflex control of pupils with light 3) Superior Colliculus (midbrain) - Match eye movements to head movement 4) Lateral Geniculate Nucleus (thalamus) - Sensation of vision

Question 31

Where do the Axons from ganglion cells in nasal retina cross?

Answer 31

**Optic chiasm** to project **contralaterally**

Question 32

Where do the Axons from ganglion cells in temporal retina project?

Answer 32

Ipsilaterally

Question 33

What happens when both eyes are open?

Answer 33

- The outer regions of our visual field is perceived by one eye only (monocular vision) - The central portion the visual fields from the two eyes overlap (binocular vision)

Question 34

What does the ability to compare overlapping information from the two eyes allow for?

Answer 34

For **depth perception** and improves our ability to **judge distances**