L06: Eye & Vision

Question 1

What is the difference between the sclera and cornea?

Answer 1

Sclera = fibrous connective tissue contunous with dura of optic n, becomes cornea as it covers the iris
Seperated by corneal limbus

Question 2

Where do extraoccular muscles attach?

Answer 2

Sclera

Question 3

What is the uvea?

Answer 3

Pigemented part of eye composed of iris, ciliary body & choroid

Question 4

What is the choroid?

Answer 4

Vascular layer of the eye, found between retina & sclera

Question 5

What is the ciliary body?

Answer 5

Connects iris to choroid, contains ciliary muscles

Question 6

What is the retina?

Answer 6

Neural layer of eye containing rods + cones

Question 7

Types of humour found in the eye

Answer 7

Vitreous - behind the lens, viscous + jelly like, enables eye to retain spherical shape
Aqueous - anterior to lens, nourishes the avascular cornea

Question 8

Describe the flow of aqueous humour through the eye

Answer 8

Produced constantly in the posterior chamber, flows into anterior chanber (in front of lens) via pupil. It is then reabsorbed into the aqueous vein at the closed angle

Question 9

What causes glaucoma?

Answer 9

Increased intraocular P –> compression of retinal arteries –> blindness
Due to insufficient reabsorption of aqueous humous

Question 10

Types of glaucoma?

Answer 10

Angle closure: irs adheres to cornea blocking reabsorption, rapid + serious
Open-angle (more common) - sclerosis of veins –> gradual reduction of vision

Question 11

How can glaucoma be treated?

Answer 11

Surgery to remove adherance, B blocker to reduce production of aq humour, PG analogue to cause local vasodilation (eye drops)

Question 12

How do light impulse get to brain?

Answer 12

Photoreceptors or retina (rods & cones) –> bipolar cells –> ganglion cells (direct)
Or indirectly invovling amacrine + horizontal cells

Question 13

What forms the optic nerve?

Answer 13

Collection of ganglion cells

Question 14

Difference between rods and cones

Answer 14

Both have outer segment containing photopigments, inner segment + synapse
Rods contain rhodopsin pigment - detects intensity of light rather than colour
Cones contain opsins so can detect diff wavelengths –> colour vision

Question 15

Which is more sensitive to light, rods or cones?

Answer 15

Rods

Greater light level to activate cones

Question 16

What is the blind spot?

Answer 16

Region on retina where optic nerve leaves eye, no photoreceptors

Question 17

What is the fovea?

Answer 17

Area of retina where visual acuity is highest, highest densitiy of cones (but light sensitivity is low)

Question 18

What is the macula?

Answer 18

Central part of retina (also contains fovea)
More cones than rods
1 cone per ganglion cell

Question 19

What is the peripheral retina?

Answer 19

Area where there is almost all rods so high light sensitivity
Many rods per ganglion cell –> spatial summation & amplification of light
Hence low visual acuity

Question 20

What is rhodopsin composed of?

Answer 20

Retinal - chromophore that changes shape in response to light
Opsin - GPCR

Question 21

How does phototransduction occur in rods in the dark?

Answer 21

Rhodopsin is quiescent
cGMP gated cation channels open allowing Na influx
Depolarisation –> glutamate release to bipolar cell
ROD IS ONN WHEN NO LIGHT PRESENT

Question 22

What is the receptive field?

Answer 22

region of retina that influences single ganglion/bipolar cell

Question 23

How do on-centre bipolar cells behave in the light?

Answer 23

Rod is OFF & stops releasing glutamate

W/o glutamate, bipolar cell is depolarised & released glutamate that excites ganglion cells

Question 24

How do on-centre bipolar cells beave in dark?

Answer 24

Rod is ON & releasing glutamate. Glutamate causes on cells to be hyperpolarised so won’t release glutamate. Hence ganglion won’t be firing APs

Question 25

How do off-centre bipolar cells behave in the light?

Answer 25

Rod is OFF & stops releasing glutamate

W/o glutamate, off bipolar cell will be hyperpolarised & won’t release glutamate.

Question 26

How do off-centre bipolar cells behave in the dark?

Answer 26

Rod is ON & releasing glutamate. Glutamate causes off cells to be depolarised so releases glutamate. Hence ganglion cells are excited & firing APs.

Question 27

What happens in the surround of the retina?

Answer 27

Opposite to the centre - in the LIGHT, on cells are hyperpolarised & off cells are depolarised
Due to action of amacrine & horizontal cells