2 - RETINA

Question 1

ophthalmoscope

Answer 1

instrument for looking into ones eye through the pupil

• used by optometrists and physicians
• can see optic disk and macula
• dark patch of macula is the fovea
• area of eye visible = FUNDUS

Question 2

optic disc

Answer 2

the roughly circular yellow region with long branching tendrils (blood vessels) over the surface of the retina coming out

• where the blood vessels leave and enter the eye
• where ganglion axons leave the eye to the brain (head of the optic nerve)

no photoreceptors or neurons = blindspot

Question 3

sclera

Answer 3

tough, fibrous outer ‘skin’

Question 4

order of cell layers in retina

Answer 4

thin ganglion layer closest to retinal surface

intermediate cell layer

bottom layer (photoreceptors) - rods and cones

pigment epithelium

(all are transparent)

Question 5

why stain retina samples

Answer 5

because they’re transparent to let light in to the photoreceptors

• but blood vessels aren’t transparent (on the retinal surface)
• so can block and prevent light from reaching the photoreceptors

Question 6

cells in the retina are neurons

Answer 6

they are formed from nervous tissue

• all cells in figure 8 (wk1, pg10) are all neurons
• including photoreceptors
• retinas are considered part of the brain
• only part of the brain that doesn’t require opening the skull to see

Question 7

neurites

Answer 7

the axons and dendrites of the neuron cell bodies

found in the layers between the cell bodies

THEY DO NOT TRANSMIT ACTION POTENTIALS

• they communicate via passive conduction of ion currents to the neurons in the next layer
• ‘neurites of the photoreceptors make synaptic connections with the neurites and cell bodies in the intermediate cell layer and the neurites of those cells make synaptic connections with the cells in the top layer’

📣SIGNAL TRANSMISSION FROM BOTTOM TO TOP

☀️LIGHT TRANSMISSION FROM TOP TO BOTTOM

Question 8

bipolar cells

Answer 8

transmit signals between photoreceptors and ganglion cells (ganglion cell layer is 1 cell thick)

Question 9

amacrine cells

Answer 9

connects to ganglion cells (kinda horizontally)

Question 10

photoreceptors

Answer 10

sensory neuron

relatively long and thin cells

light sensitive part is the outer segments (contains opsins)

cell bodies aren’t light sensitive

Question 11

rods

Answer 11

long thin photoreceptors

• only respond when light stimulation is low

Question 12

cones

Answer 12

shorter and fatter photoreceptors

Question 13

opsins

Answer 13

light sensitive proteins found in the outer segments of photoreceptors

Question 14

inner segment of photoreceptors

Answer 14

part that is between cell body and outer segments

Question 15

order of structure of photoreceptors

Answer 15

neurites (axons)

cell bodies

inner segments

outer segments

Question 16

in a micrograph of a horizontal slice through the receptor level, the dots with the circular gap around are cones

• this is seen about 6-10mm from the macula centre

Answer 16

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Question 17

daytime vision (photopic)

Answer 17

cones

they need a lot more stimulation so require more light to respond

Question 18

nighttime vision (scotopic)

Answer 18

rods

respond to low light stimulation

• due to few rods in the fovea = cannot see fine details at night
• ‘night blind at the very centre of our vision’ (foveola)

Question 19

macula

Answer 19

contains lots of photoreceptors (vast majority of all cones)

• fovea seen through ophthalmoscope
• darkest region in centre = FOVEOLA (only cones)

Question 20

parafovea

Answer 20

fuzzy region that extends the macula

• extends about 0.5mm from the foveal boundary
• lines on graph of cone and rod density cross at about 1mm from retinal centre
• densities equal (about 40,000/mm^2)

Question 21

order of macula structures

Answer 21

foveola > fovea > parafovea

Question 22

foveola

Answer 22

the very bottom of the depression in the centre of the macula

• 0.3mm in diameter
• only the bottom layer (photoreceptor layer) and their neurites
• the cell bodies above have been swept away and are found distributed around the foveola
• no retinal cell bodies over the photoreceptors
• no blood vessels
• only CONES
• high density of about 200,000 per square mm
• NO RODS
• cones here are rod shaped
• means nearly half the cones in the retina aren’t even cone shaped
• ‘highest density of photoreceptors than anywhere in the retina’

Question 23

fovea

Answer 23

the depression in the macula

• includes the sides and bottom of the depression
• 1.5mm across
• mostly cones
• few rods (most near or at the foveal boundary)
• ‘no blood vessels to prevent light from reaching the photoreceptors’
• the clearest image
• need to position eyes so that the image falls on the fovea

Question 24

clinical macula

Answer 24

seen through an ophthalmoscope

• central part of the anatomical macula
• dark patch on retina

Question 25

anatomical macula

Answer 25

defined by cellular anatomy rather than observed through a clinical eye exam - the depth of cells in the ganglion layer is used to distinguish the anatomical macula - twice as wide as the clinical macula

Question 26

ganglion cell layer depths

Answer 26

1 cell = outside anatomical macula two or more cells = inside anatomical macula - none in foveola - thickest in parafovea

Question 27

perifovea

Answer 27

completely outside the clinical macula - ‘annular region of the anatomical macula that surrounds the parafovea’ - cone density of around 10,000/mm^2 - around 1.3mm from macula centre

Question 28

peripheral retina

Answer 28

‘region of the retina outside of the anatomical macula’ - mainly rods - few cones - cone density outside the macula = 3-4000/mm^2 - around 5mm from macula centre - but a very cone rich zone at the edge of the retina

Question 29

rod density

Answer 29

peak density = 150,000/mm^2 temporal side = 4mm nasal side = 6mm (just beyond the optic disk) - edges of retina = 50,000-70,000/mm^2 - no rods in centre of macula - peaks around 4mm from macula centre

Question 30

how many rods and cones in the human retina?

Answer 30

90 million rods 6 million cones - area under the density cure for rods is about 20x that of the cones

Question 31

graph of densities on pg 17 of week 1

Answer 31

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Question 32

what makes a cell a rod or cone

Answer 32

the sensitivity to light stimulation not the shape!! as some cones are rod shaped

Question 33

how to see stars at night

Answer 33

- don’t look directly at them because it’ll fall on the foveola which doesn’t have night vision (has no rods) - so look out the corner of your eye at it and you’ll see it better

Question 34

cone density

Answer 34

around 200,000 per mm^2 in centre of macula - highest density in retina ^ - drops to about 1000-2000 per mm^2 - cones seem smaller in centre of macula

Question 35

there is a vascular zone surrounding the fovea - having no blood vessels and no cell bodies above the photoreceptors means light can access the photoreceptors in the fovea easier

Answer 35

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