Visual System 1.5

Question 1

What is the retina?

Answer 1

Very thin layer of tissue that lines the inner part of the eye

Question 2

What is the retina responsible for?

Answer 2

1. capturing the light rays that enter the eye

2. these light impulses are then sent to the brain for processing, via the optic nerve.

Question 3

What does the optic nerve do?

Answer 3

transmits electrical impulses from the retina to the brain

Question 4

Where does the optic nerve connect?

Answer 4

to the back of the eye near the macula

Question 5

What is the visible portion of the optic nerve called?

Answer 5

optic disc (corresponding anatomic landmark for physiological blind spot)

Question 6

Where is the blind spot?

Answer 6

Where the optic nerve meets the retina there are no light sensitive cells

Question 7

Where is the macula?

Answer 7

roughly in the centre of the retina, temporal to the optic nerve

Question 8

What is the macula?

Answer 8

• small and highly sensitive part of the retina responsible for detailed central vision
• allows us to appreciate detail and perform tasks that require central vision such reading

Question 9

What is the fovea?

Answer 9

the very centre of the macula and most sensitive part of retina

Question 10

What is the concentration of rods and cones in the fovea?

Answer 10

• Highest conc of cones

- Lowest conc of rods

Question 11

What is central vision?

Answer 11

• Detail day vision, colour vision

- Reading, facial recognition

Question 12

How do you asses central visions?

Answer 12

visual acuity assessment

Question 13

What does loss of foveal vision lead to?

Answer 13

Poor visual acuity

Question 14

What is perisperhal vision?

Answer 14

• Shape, movement, night vision

- Navigation vision

Question 15

How is peripheral vision assessed?

Answer 15

by visual field assessment

Question 16

What happens if there is is extensive loss of visual field?

Answer 16

unable to navigate in environment, patient may need white stick even with perfect visual acuity

Question 17

What is the outer layers of the retinal structure?

Answer 17

• Photoreceptors (1st order neuron)

- Detection of Light

Question 18

What is the middle layer of retinal structure?

Answer 18

• Bipolar Cells (2nd order neuron)

- Local signal processing to improve contrast sensitivity, regulate sensitivity

Question 19

What is the inner layer of retinal structure?

Answer 19

• Retinal ganglion cells (3rd order neuron)

- Transmission of signal from the eye to the brain

Question 20

What does the retina form?

Answer 20

the innermost layer of the coat of eye in the posterior segment

Question 21

What does the retina consist of?

Answer 21

• an outer thin layer of Retinal Pigment Epithelium, situated right in front of the Choroid,
• inner thicker layer called the Neuroretina.

Question 22

What does the retinal pigment epithelium do?

Answer 22

transports nutrient from the choroid to the photo-receptor cells,
and removes metabolic waste from the retina

Question 23

What is the neuroretina made up of?

Answer 23

photo-receptors and neurons

Question 24

What are the layers of retina?

Answer 24

1. Outer Layer consisting of photo-receptors,
2. middle layer of intermediate neurons
3. inner layer of ganglion nerve cells
   - axon running along the optic nerve into the brain

Question 25

What are rods?

Answer 25

1. Longer outer segment with photo-sensitive pigment 2. 100 times more sensitive to light than cones 3. Slow response to light 4. Responsible for night vision (Scotopic Vision) 120 million rods

Question 26

What are cones?

Answer 26

1. Less sensitive to light, but faster response 2. Responsible for day light fine vision and colour vision (Photopic Vision) 6 million cones 3. Shorter outer segment

Question 27

Where are photopigments synthesised?

Answer 27

inner photo-receptor segment, | and are then transported to the outer segment

Question 28

What is the outer segment made of?

Answer 28

stacks of discs

Question 29

What are distal discs?

Answer 29

The distal discs with deactivated photo-pigments are shedded from the tips, and phago-cytosed by the retinal epithelial cells

Question 30

What happens to the deactivated photopigments?

Answer 30

The deactivated photopigments are regenerated inside the retinal epithelial cells, and then transported back to the photo-receptors

Question 31

What is rod (scotopic) vision?

Answer 31

1. Peripheral and night vision 2. More photoreceptors 3, More pigment 4. Higher spatial and temporal (time) summation 5. Recognizes motion

Question 32

What is cone (photic) vision?

Answer 32

- Central and day vision | - Recognizes colour and detail

Question 33

Where is rod density highest?

Answer 33

Rod photo-receptors are widely distributed all over the retina, with the highest density just outside the macula (tails off towards periphery)

Question 34

Are rod photoreceptors in the macula?

Answer 34

NO

Question 35

Where are cone photoreceptors?

Answer 35

distributed only within the macula

Question 36

Where can you find the highest conc of rod photoreceptors in retina?

Answer 36

20-40 degrees away from fovea

Question 37

Where is the peak light sensitivity for rod vision?

Answer 37

498 nano-meters wavelength

Question 38

What are the different cones and colours?

Answer 38

S-Cones: Blue (short wavelength) M-Cones: Green L- Cones: Red (long wavelength)

Question 39

What is yellow light?

Answer 39

1. wavelength between the peak sensitivity wavelengths of M-Cones and L-Cones. 2. Yellow light stimulates both M-cones and L-cones equally. 3. Biologically, we experience yellow light as a combination of green and red light.

Question 40

What is the commonest form of colour vision deficiency?

Answer 40

Deuteranomaly

Question 41

What is deuteranomaly caused by?

Answer 41

shifting of the M-cone sensitivity peak towards that of the L-cone curve, causing red-green confusion - don't perceive red

Question 42

What is the name for full colour blindness?

Answer 42

achromatopsia

Question 43

What is the prevalence of colour vision deficit?

Answer 43

8% amongst males, | and 0.5% amongst females

Question 44

What is anomalous trichromatism?

Answer 44

Colour Vision deficits can be caused by a shift in the photo-pigment peak sensitivity

Question 45

What is commonest form of anomalous trichromatism?

Answer 45

Deuteranomaly

Question 46

What is dichromatism?

Answer 46

only two cone photo-pigment sub-types are present

Question 47

What is monochromatism?

Answer 47

complete absence of colour vision

Question 48

What is blue cone monochromatism?

Answer 48

- presence of only blue L-cones | - normal day light visual acuity

Question 49

What is rod cone monochromatism?

Answer 49

- total absence of all cone photo-receptors | - no functional day vision