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Year 3 Exam 2 > The eye > Flashcards

The eye Flashcards

1
Q

What are rods responsible for?

A

Black and grey vision.

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2
Q

What are cones responsible for?

A

Colour vision

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3
Q

Where are photoreceptors located in the eye?

A

The retina

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4
Q

Do cones have a high or low sensitivity to light?

A

Low (they need bright light for colour vision)

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5
Q

Do rods have a high or low sensitivity to light?

A

High

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6
Q

Where are cones most abundant?

A

Fovea

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7
Q

Where are rods most abundant?

A

Periphery of the retina.

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8
Q

How do cones produce a higher resolution image than rods?

A

Cones have little or no convergence, 1:1 ratio of cone to ganglion cell.

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9
Q

Why do rods produce a lower resolution image than cones?

A

Rods are highly convergent, many rods feed into one ganglion cell.

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10
Q

What is opsin?

A

A G protein-coupled receptor found in photopigment.

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11
Q

What is retinal?

A

Opsin’s ligand.

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12
Q

How many photo pigments are there in cones?

A

3 (red, green, blue)

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13
Q

How many photopigments are there in rods?

A

1

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14
Q

What is the name of the photopigment found in rods?

A

Rhodopsin

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15
Q

Which vitamin is retinal derived from?

A

Vitamin A.

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16
Q

What is the process of visual transduction?

A
  1. Retinal is activated by light
  2. This causes it to change shape from 11-cis-retinal to all-trans-retinal
  3. This then causes a conformational change in the opsin, activating it
    4.This initiates a cascade of events resulting in hyperpolarization of the photoreceptor membrane potential
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17
Q

Where in the eye does visual transduction occur?

A

The retina

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18
Q

What neurotransmitter is released during phototransduction?

A

Glutamate

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19
Q

Are the pupils dilated or constricted in bright light?

A

Constricted

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20
Q

Are the pupils dilated or constricted in the dark?

A

Dilated

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21
Q

What is astigmatism?

A

Where the surface of the cornea is uneven.

22
Q

How does the eye accommodate far vision?

A
  • Ciliary muscle is relaxed.
  • Lens is pulled taut “flat and thin”
23
Q

How does the eye accommodate near vision?

A
  • Ciliary muscle is contracted
  • Lens has a higher curvature
24
Q

Contraction of the ciliary muscle is controlled by which nervous system?

A

Parasympathetic nervous system

25
Q

What is presbyopia?

A

This is where the lens is less flexible so can’t become rounded. This makes it impossible to focus on near objects.

26
Q

What is shortsightedness?

A

This is where the eyeball is too long so light is focussed in front of the retina.

27
Q

What is longsightedness?

A

This is where the eyeball is too short so near objects are brought into focus behind the retina.

28
Q

What are the two routes of drug administration to the eye?

A

Peribulbar and Retrobulbar

29
Q

What are the anatomical barriers for ocular drug delivery?

A
  • Layers of the cornea
  • Conjunctiva
  • Sclera
30
Q

What are the precorneal factors that can effect ocular drug delivery?

A
  • Solution drainage
  • Blinking
  • Tear film
  • Tear turn over
31
Q

What is the role of mucin?

A

Mucin is present in the tear film. It forms a hydrophilic layer that moves over the glycocalyx of the ocular surface and clears debris and pathogens.

32
Q

What are the considerations needed for ophthalmic formulations? (4)

A
  • Osmolality
  • pH
  • Surface tension
  • Viscosity
33
Q

What is the definition of osmolality?

A

The concentration of a solution expressed as the total number of solute particles per kilogram of solvent ( mOsmol/kg or mmol/kg)

34
Q

What is the osmolality of heathy eyes?

A

~302mmol/kg

35
Q

What is the effect of hypotonic solutions on the eye?

A

Increases corneal epithelial permeability causing oedema

36
Q

What is the effect of hypertonic solutions on the eye?

A

Dehydration of the corneal epithelium

37
Q

What is the pH range that eyes can tolerate?

A

3.5-9

38
Q

What is the pH range of tears?

A

6.9-7.5

39
Q

What pH should ocular drugs be?

A

As close to physiological tear pH as possible: 6.9-7.5

40
Q

What is the surface tension of healthy tear fluid?

A

43.6-46.6 mN/m

41
Q

What affect do eye drops that lower the surface tension have on the eye? (1)

A
  • They destabilise the tear film
42
Q

Why is it important that the viscosity of eye drops should be a close match to that of tears? (3)

A
  • To prolong drug retention in the tear film
  • Enhances drug absorption
  • Reduces drainage rate of the drug
43
Q

What are the limitations of topical ocular administration?- eye drops

A
  • Difficult to instil
  • Variable dosing
  • Dilution and washout occur
  • They require high drug concentrations
  • Both ocular and systemic side effects can occur
  • Major compliance and execution issues
44
Q

What are the advantages of eye solutions? (5)

A
  • Easy to manufacture
  • Lowest cost of production
  • Relatively easy to administer
  • Rapid onset of action
  • Good dose uniformity
45
Q

What are the disadvantages to eye solutions? (2)

A
  • Rapidly drained from the eye
  • Rate of drainage is proportional to the size of the drop
46
Q

What are the downsides to ocular suspensions? (4)

A
  • Particles are retained in the eye between the eyeball and eyelid
  • Limitations to particle size due to irritation
  • Polymorphic changes with storage
  • Ostwald ripening and caking
47
Q

How can a ocular suspension be altered to avoid Ostwald ripening and caking?

A

Increase viscosity

48
Q

What are advantages of ocular gels? (2)

A
  • Lower frequency of application than solutions
  • Can be activated to undergo phase transition in the eye
49
Q

What is the most efficient way of getting drugs to the back of the eye?

A

Intravitreal administration (injection directly to the back of the eye)

50
Q

What are Punctal plugs?

A

Plugs that are inserted into tear ducts where they stay for 2-3 months, releasing drugs into the eye.

51
Q

What devices are available for ocular drug delivery? (5)

A
  • Punctal plugs
  • Injectable implant
  • Ocular iontophoresis
  • Drug -eluting contact lenses
  • Topical ophthalmic drug delivery device (in human clinical trials)
52
Q

What is Sensimed triggerfish?

A

It is a contact lens which continuously measures interocular pressure.

Year 3 Exam 2 (19 decks)

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