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MPharm Y3S2 > Pharmacology CNS Eye > Flashcards

Pharmacology CNS Eye Flashcards

1
Q

What is the function of the sclera?

A

White part, protective outer coating

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2
Q

What is the function of the conjunctiva?

A

Thin membrane, covers front of eye for protection

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3
Q

What is the function of the cornea?

A

Circular transparent window at front, involved in refraction of light as it enters the eye

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4
Q

What is the function of the anterior chamber?

A

Filled with fluid called the aqueous humour

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5
Q

What is the function of the aqueous humour?

A

Provides oxygen and nutrients to transparent organs of eye (as no blood supply)
Also allows to maintain pressure (intraocular pressure- IOP) in they eye

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6
Q

What is the function of the ciliary body?

A

Contacts ciliary muscle
Secretes the AH across to lens, out to pupil then drains into the canal of schelmm, constant turnover of this fluid gives the IOP

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6
Q

What is the function of the iris?

A

Made of SM which contracts and relaxes so pupil can dilate and constrict

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7
Q

What is the function of the lens?

A

Transparent organ, allows light through, role is to fine focus the light onto the retina

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8
Q

What is the function of the sensory ligaments?

A

Attach the lens to the ciliary body

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9
Q

What is the function of the vitreous humour?

A

Fluid, viscous, absorbs energy, protect delicate structures in the eye, particularly neural retina

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10
Q

What is the function of the fovea?

A

When light comes into the eye, it is focus on the fovea- has the highest visual acuity

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11
Q

What is the function of the choroid?

A

Pigmented layer (helps absorb light), highly vesicular, provides blood supply for outer layer of retina

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12
Q

What is the function of the optic disc?

A

Blind spot- where all of axons from retina go out of eye forming the optic nerve, takes visual info to brain

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13
Q

What muscle is involved in controlling pupil size?

A

In the iris
Circular SM
Radial SM

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14
Q

Describe what occurs in the present of light to pupil size:

A

Parasympathetic NS
Pupillary constriction
Circular- fibres of muscle in circular fashion, when fibres contract, pupils get smaller

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15
Q

Describe what occurs in the absence of light to pupil size:

A

Sympathetic NS
Pupillary dilation
Radial- fibres which run radially, when fibres contract fibres become shorter

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16
Q

Describe how light is focused?

A

The first point in focussing light is the cornea- greatest degree of refraction, the lens fine focuses onto retina
Important that cornea is smooth in order that refraction occurs evenly

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17
Q

What medical condition is present if the cornea isn’t smooth and how is this fixed?

A

Astigmatism
Laser correction surgery (LASIK) changes the degree of curvature of the cornea

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18
Q

What is accommodation of the eye?

A

In order to fine focus light, the curvature of the lens is altered

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19
Q

Describe accommodation for far vision:

A

Ciliary muscle is relaxed (parasympathetic NS off)
Lens is pulled taut (flat and thin) by IOP so less curvature and can focus parallel light coming from a distant point

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20
Q

Describe accommodation for near vision:

A

Cilliary muscle is contracted (circular muscle contracts)
Lens has higher curvature (rounder as not under tension)
Increased curvature means more refraction so can focus light from close object
Contraction of the ciliary muscle is mediated by the parasympathetic NS

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21
Q

What occurs as the image is focused on the fovea after accommodation?

A

It is upside down and back to from but the brain fixes it

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22
Q

What is presbyopia?

A

Lens less flexible- no longer able to become rounder therefore it is not possible to focus on near object
Common with older age

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23
Q

What is short sightedness?

A

Myopia
Eyeball is too long- parallel light is focused in front of retina
Means can see things that are close but not far away

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24
Q

What is long sightedness?

A

Hyperopia
Eyeball is too short- near objects are brought to a focus behind the retina
So can’t see close but far vision is fine

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25
Q

Does ciliary muscle have an effect on pupil size?

A

No it is independent to pupil size
Other SM is involved in pupil size

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26
Q

Describe the function of the retina:

A

The light sensitive part of the eye
It is responsible for visual transduction (converting light energy to electrical chemical signals for neurons)
Photo receptors do this

27
Q

What are photoreceptors?

A

Are sensory receptors of the retina which transduce light energy of specific wave length (the visible spectrum 400-700nm) into electrical signals
Have rods and cones

28
Q

What are the rods responsible for in photoreceptors?

A

100 million rods
For black and white vision (greyscale)- high sensitivity to light, night vision, so can’t distinguish colour at night
Abundant in periphery, so in peripheral vision can’t detect colour vision
Highly convergent, many rods (up to 100) feed into 1 ganglion cell- low resolution high sensitivity

29
Q

What are the cones responsible for in photoreceptors?

A

6 million cones
Colour vision- low sensitivity to light so need bright light in day vision
Abundant in fovea
No convergence, 1:1 with ganglion cell so high resolution

30
Q

Describe the steps in the visual processing of the retina:

A

Photoreceptors synapse with bipolar cells which then synapse with retinal ganglion cell which then take the electrical signals to the retina to the brain via their axons to fibres of optic nerve
Horizontal cells and Amacrine cells go across the retina, important for lateral processing

31
Q

Name the structures of the photoreceptors:

A

Outer segments
Inner segments- metabolic centre (nucleus, mitochondria)
Synaptic terminal- synapse with bipolar cells

32
Q

Describe the outer segment of photoreceptors:

A

Detects light stimulus (contain photopigment)
Most posterior part of retina
Consists of flattened, stacked membranous discs
Turned over by the cells of the retinal pigment epithelium (RPE)

33
Q

What is the function of the retinal pigment epithelium (RPE)?

A

Phagocytosis some discs each day- enables constant turnover to prevent accumulative damage by light

34
Q

Describe why the fovea can give a fine resolution of an image:

A

More cones- 1:1 coupling
Lateral inhibition, when 1 photoreceptor is stimulated it switches next photoreceptor off
Other areas of the retina are moved aside here, so light doesn’t travel through other layers of the retina

35
Q

Describe the importance of photopigment in photoreceptors:

A

Found in the outer segment which capture light energy for transduction

36
Q

Describe the structure and function of the photopigment:

A

Consists of a protein- opsin
And retinal (aka retinene) which absorbs light- the chromophore
Opsin is a GPCR and retinal is its ligand
Retinal deficiency can cause blindness as derived from vit A

37
Q

Name and describe the 4 different photopigments:

A

1 in rods (rhodopsin)- sensitive to all wavelengths of visible light
3 in cones- red, green, blue light sensitive

38
Q

Describe the process of visual transduction:

A

When the retinal is activated by light it changes shape, from 11-Cis-Retinal (bent) to all-trans-retinal
This in turn causes a conformational change in the opsin, activating it and initiating a cascade of events resulting in hyperpolarisation of the photoreceptor membrane potential

39
Q

Describe the photoreceptor activity in the dark:

A

Outer segments of the photoreceptor contain a cGMP-gated cation channel on its inner surface
cGMP opens the cation channel, allowing Na+ to move into cell down its electrochemical gradient (depolarise)
In the dark cGMP levels are high due to the action of GC converting GTP to cGMP, the cGMP-gated cation channels are therefore open
Movement of Na+ into cell causes depolarisation (to -40mV)
Depolarisation causes opening of VG Ca2+ channels in the synaptic terminal
Ca2+ influx causes NT release therefore in the dark the photo receptor is depolairsed and is releasing NT

40
Q

Describe the photoreceptor activity in the light:

A

Light causes 11-Cis-retinal to change conformation to all-trans-retinal
This causes a conformational change- stim of its GPCR activity
Transducin is the G protein associated with the receptor
Activation of the transducin in turn activates phosphodiesterase activity
Increase phosphodiesterase activity degrades cGMP
Decrease cGMP levels close the cGMP gated cation channels
Closure of this channel means Na+ is no longer moving into the cell and therefore there is hyperpolarisation of the membrane potential
This causes VG Ca2+ channels to close and in turn decreases the amount of NT release
In light, the photoreceptor is hyperpolarised and NT release is decreased

41
Q

Describe the aspect of NT in phototransduction:

A

NT released is glutamate
The response to light is graded, the brighter the light, the less NT will be released (as bigger hyperpolarisation)
As few as 5 photons can evoke the sensation of light

42
Q

Describe the termination of phototransduction signal:

A

After activation the photopigments are ‘bleached’ and remain unresponsive until recycling of the retinal has occurred
This terminated the signal and is mediated by enzymes which convert all-trans-retinal back to 11-cis-retinal (RPE cells)

43
Q

Which cones will green cones stimulate?

A

Red, green and blue cones

44
Q

Which cones will red cones stimulate?

A

Red only

45
Q

Which cones will yellow light stimulate?

A

Red and green, not blue

46
Q

What occurs in colour blindness?

A

Lacking one of the cones

47
Q

Describe the visual pathways:

A

Light from right side of visual field goes to left side of eye. Info from left side of retina goes to left side to brain
Light from left side of visual field goes to right side of eye. Info from right side of retina goes to right side of brain

48
Q

What is optic chiasm?

A

Cross over when info from right visual field, left side of right eye needs to go to left side of brain and vice versa

49
Q

Describe the processing of the visual pathway:

A

Rental ganglion, optic nerve, thalamus, lateral geniculate nucleus of thalamus, synapse here, visual cortex (back of brain in occipital lobe)

50
Q

What is the function of the aqueous humour?

A

Supplies nutrients and removes waste products from the avascular organs of the anterior eye (lens and cornea)

51
Q

What rate is the aq humour produced?

A

2-3µl/min

52
Q

Which 2 pathways can the aq humour leave from?

A

70-90% leaves via the ‘conventional outflow pathway’
10-30% leaves via the ‘non conventional pathway’ aka ‘uveoscleral pathway’

53
Q

Describe the conventional outflow pathway:

A

Trabecular meshwork to schlemm’s canal to episcleral BVs

54
Q

Describe the non conventional pathway:

A

Intercellular spaces between the ciliary muscle fibres, choroid and out via sclera
This component may be greater in patient with glaucoma

55
Q

How is the aq humour produced?

A

By ciliary epithelium
Has ciliary processors, pigmented to non-pigmented, which increase SA for secretion of aq
Have gap and tight junctions
Melanin granules for pigment
Na+, Cl- and HCO3 moves from blood to posterior chamber via ciliary epithelium which allows water to move with them too via aquaporins

56
Q

How is aq humour secreted?

A

Active process
Produced under autonomous (sympathetic) control
NA/adrenaline binds to B2 receptor (post synaptic) causes increase in AH production
This then stims Na/K+ pump
If NA binds to a2 receptor (pre synaptic) it causes a decrease in AH production
Carbonic anhydrase activity is necessary in production of AH, converts CO2 and H2O to HCO3-, inhibition of CA causes decrease in AH production

57
Q

What are BBs contraindicated in?

A

Bradycardia and heart block

58
Q

What are the ocular SEs of BB?

A

Most due to preservative
Stinging, dry eye, itching, pain, erythema, corneal disorders

59
Q

Describe the outflow pathway of aq humour:

A

Aq outflow via the trabecular meshwork is:
-facilitated by constriction of the pupil- iris is stretched out so keeps angle open
-inhibited by dilation of the pupil- iris muscle thicker, physical blocking
-faciliated by contraction of the ciliary muscle, pupil more taut

60
Q

What causes pupillary constriction (pupils smaller)?

A

Mediated by parasympathetic NS
Ach via muscarinic (M3) receptors

61
Q

What causes pupillary dilation (pupils larger)?

A

Sympathetic NS
NA via a1 adrenergic receptors

62
Q

What causes innervation of the ciliary SM?

A

Parasympathetic innervation
ACh leads to contraction muscarinic (M3) receptors

63
Q

How do muscarinic agonists work in glaucoma?

A

Increase aq outflow
Stimulate the M3 receptor

64
Q

Name an example of a muscarinic agonist and how it works:

A

Pilocarpine- less freq used due to SEs, blurred vision
Constriction of pupil (myopic effect)
Contraction of the ciliary muscle
Facilitation of drainage via canal of Schelmm

65
Q

How do PG analogues work?

A

Increase AH outflow via the uveoscleral pathway
Analogues of PGF2a act at PGFr (exception bimatoprost)
Decreases IOP mainly by increasing (2x) aq outflow via the uveoscleral pathway
Increase degradation of extracellular matrix within sclera, increases flow

66
Q

What are the SEs of PG analogues?

A

Conjunctival hyperaemia (bloodshot eyes), foreign body sensation, ocular irritation- due to drugs, not P
Eyelash lengthening, thickening, hyperpigmentation
Iris hyperpigmentation (11-23%) most common with green-brown irises

MPharm Y3S2 (22 decks)

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