The Eye and Retina

Question 1

What is retinitis pigmentosa?

Answer 1

A genetic disorder that results in total blindness

Question 2

What is the stimulus for vision?

Answer 2

Light

Question 3

What is wavelength?

Answer 3

The distance between peaks of the electromagnetic waves

Question 4

What is visible light?

Answer 4

The energy within the electromagnetic spectrum that humans can perceive

Question 5

What are the range of wavelengths that humans can perceive?

Answer 5

400-700 nm

Question 6

Where does light pass through?

Answer 6

The pupil and the aqueous humor

Question 7

What focuses light?

Answer 7

The cornea and the lens

Question 8

Why does light need to be focused?

Answer 8

To form sharp images of objects on the retina

Question 9

What are the two types of photoreceptors?

Answer 9

Rods and cones

Question 10

What are visual pigments?

Answer 10

Light-sensitive chemicals in the outer segments of the receptors that react to light and trigger electrical signals

Question 11

What is the optic nerve?

Answer 11

Nerve fibre that conducts signals from the retina to the brain

Question 12

When do pupils dilate?

Answer 12

To allow more light to enter the eye in dark conditions

Question 13

When do pupils constrict?

Answer 13

To allow less light to enter the eye in bright conditions to protect the eyes

Question 14

What is accommodation?

Answer 14

Ciliary muscles change shape of the lens, altering its focal length which keeps the image focused on the retina

Question 15

What is presbyopia?

Answer 15

Elasticity in the eye decreases as we age, making near point further away

Question 16

What is the fovea?

Answer 16

An area in the centre of the retina that only contains cones

Question 17

What is the peripheral retina?

Answer 17

Includes all of the retina outside of the fovea
Contains rods and cones

Question 18

What is macular degeneration?

Answer 18

Destruction of the cone-rich fovea and a small area that surrounds it
Creates a blind region in central vision

Question 19

What is retinitis pigmentosa?

Answer 19

A degeneration of the retina that is passed from one generation to the next
First attacks the peripheral rod receptors and results in poor vision in the peripheral field

Question 20

What is the blind spot?

Answer 20

An area on the retina with no photoreceptors
Where the nerve fibres that make up the optic nerve leave the eye

Question 21

Why aren’t we aware of our blind spot?

Answer 21

The blind spot is located off to the side of our visual field where objects are not in sharp focus anyways

Our brain fills in the place where the image disappears

Question 22

What is the cornea?

Answer 22

Transparent covering the front of the eye
Cannot move
80% of eye’s focusing power

Question 23

What is the lens?

Answer 23

Remaining 20% of eye’s focusing power
Can change its shape to adjust the eye’s focus

Question 24

What are refractive errors?

Answer 24

Errors that can affect the ability of the cornea and/or lens to focus the visual input onto the retina

Question 25

What is myopia?

Answer 25

An inability to see distant objects clearly Occurs when light is focused in front of the retina

Question 26

What is refractive myopia?

Answer 26

The cornea and/or the lens bends the light too much

Question 27

What is axial myopia?

Answer 27

The eyeball is too long

Question 28

What is hyperopia?

Answer 28

When light is focused behind the retina Eyeball is too short

Question 29

What is visual transduction?

Answer 29

Photoreceptors transforms light into electricity

Question 30

What are the two parts of visual pigments?

Answer 30

Opsin and retinal Both of these together absorb visible light

Question 31

How is transduction in the eye initiated?

Answer 31

The visual pigment absorbs light which makes the retinal change shape from bent to straight and this creates a chemical chain reaction

Question 32

What is dark adaptation?

Answer 32

The process of increasing sensitivity in the dark

Question 33

What is the dark adaptation curve?

Answer 33

The function relating sensitivity to light to time in the dark, beginning when the lights are extinguished

Question 34

How do we measure the dark adaptation curve?

Answer 34

The participant adjusts a flashing light to be just barely visible and as the eyes adapt to the dark they keep adjusting the light to be just barely visible

Question 35

What is the cone adaptation experiment?

Answer 35

Repeat original experiment but with light shined just on the fovea

Question 36

What is the rod adaptation experiment?

Answer 36

Measured with rod monochromats because they have no cones

Question 37

What is visual pigment bleaching?

Answer 37

When the retinal changes shape and separates from the opsin, the molecule becomes lighter in colour Pigments in their bleached state are no longer useful for vision

Question 38

What is visual pigment regeneration?

Answer 38

When retinal returns to its bent shape and becomes reattached to the opsin

Question 39

What is retina deattachment?

Answer 39

When a person's eyes become detached from the pigment epithelium which causes blindness in the area where the separation occured

Question 40

What is spectral sensitivity?

Answer 40

The eye's sensitivity to light as a function of the light's wavelength Measured by determining the spectral sensitivity curve (relationship between wavelength and sensitivity)

Question 41

What is the Purkinje shift?

Answer 41

Enhanced perception of short wavelengths during dark adaptation -better at seeing blues/greens

Question 42

What does the rod pigment absorb best at?

Answer 42

500 nm

Question 43

What do photoreceptors synapse to?

Answer 43

Bipolar cells

Question 44

What do bipolar cells connect to?

Answer 44

Ganglion cells

Question 45

What are the 2 types of ganglion cells?

Answer 45

P and M

Question 46

What are horizontal cells?

Answer 46

Make lateral connection among receptors and bipolar cells

Question 47

What are amacrine cells?

Answer 47

Laterally connect among bipolar and ganglion cells

Question 48

What is neural convergence?

Answer 48

Occurs when a number of neurons synapse onto a single neuron

Question 49

Compare rods and convergence?

Answer 49

Rods converge more than cones do Results in better sensitivity than cones

Question 50

Compare cones and convergence?

Answer 50

Cones have better detail vision than rods due to less neuron convergence

Question 51

What is visual acuity?

Answer 51

The ability to see details

Question 52

What is the receptive field?

Answer 52

The region of the retina that must receive illumination in order to obtain a response in any given fibre

Question 53

What are center-surround receptive fields?

Answer 53

The area in the center of the receptive field responds differently to light than the area in the surround of the receptive field

Question 54

What are excitatory-center, inhibitory-surround receptive fields?

Answer 54

Stimulation in the center = increases firing Stimulation in the surround = decreases firing

Question 55

What are inhibitory-center, excitatory-surround receptive fields?

Answer 55

Stimulation in the center = inhibitory Stimulation in the surround = excitatory

Question 56

What is the center-surround antagonism effect?

Answer 56

When light covers both the excitatory and inhibitory fields, the effects will counteract each other

Question 57

What size of light do neurons respond best to?

Answer 57

Light that is the size of the excitatory center of the receptive field

Question 58

What is lateral inhibition?

Answer 58

Inhibition that is transmitted across the retina

Question 59

How does lateral inhibition underlie center-surround antagonism?

Answer 59

Lateral plexus transmits signals laterally in the limulus and the horizontal and amacrine cells transmit inhibitory signals laterally across the retina Center-surround receptive fields are created by the interplay of excitation and lateral inhibition

Question 60

What is edge enhancement?

Answer 60

An increase in perceived contrast at borders between region of the visual field -make edges look more distinct

Question 61

What is the preferential looking technique?

Answer 61

Two stimuli are presented and experimenter watches to determine where the participant (often an infant) is looking