The eye

Question 1

What are rods responsible for?

Answer 1

Black and grey vision.

Question 2

What are cones responsible for?

Answer 2

Colour vision

Question 3

Where are photoreceptors located in the eye?

Answer 3

The retina

Question 4

Do cones have a high or low sensitivity to light?

Answer 4

Low (they need bright light for colour vision)

Question 5

Do rods have a high or low sensitivity to light?

Answer 5

High

Question 6

Where are cones most abundant?

Answer 6

Fovea

Question 7

Where are rods most abundant?

Answer 7

Periphery of the retina.

Question 8

How do cones produce a higher resolution image than rods?

Answer 8

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

Question 9

Why do rods produce a lower resolution image than cones?

Answer 9

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

Question 10

What is opsin?

Answer 10

A G protein-coupled receptor found in photopigment.

Question 11

What is retinal?

Answer 11

Opsin’s ligand.

Question 12

How many photo pigments are there in cones?

Answer 12

3 (red, green, blue)

Question 13

How many photopigments are there in rods?

Answer 13

1

Question 14

What is the name of the photopigment found in rods?

Answer 14

Rhodopsin

Question 15

Which vitamin is retinal derived from?

Answer 15

Vitamin A.

Question 16

What is the process of visual transduction?

Answer 16

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

Question 17

Where in the eye does visual transduction occur?

Answer 17

The retina

Question 18

What neurotransmitter is released during phototransduction?

Answer 18

Glutamate

Question 19

Are the pupils dilated or constricted in bright light?

Answer 19

Constricted

Question 20

Are the pupils dilated or constricted in the dark?

Answer 20

Dilated

Question 21

What is astigmatism?

Answer 21

Where the surface of the cornea is uneven.

Question 22

How does the eye accommodate far vision?

Answer 22

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

Question 23

How does the eye accommodate near vision?

Answer 23

• Ciliary muscle is contracted
• Lens has a higher curvature

Question 24

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

Answer 24

Parasympathetic nervous system

Question 25

What is presbyopia?

Answer 25

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

Question 26

What is shortsightedness?

Answer 26

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

Question 27

What is longsightedness?

Answer 27

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

Question 28

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

Answer 28

Peribulbar and Retrobulbar

Question 29

What are the anatomical barriers for ocular drug delivery?

Answer 29

- Layers of the cornea - Conjunctiva - Sclera

Question 30

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

Answer 30

- Solution drainage - Blinking - Tear film - Tear turn over

Question 31

What is the role of mucin?

Answer 31

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.

Question 32

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

Answer 32

- Osmolality - pH - Surface tension - Viscosity

Question 33

What is the definition of osmolality?

Answer 33

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

Question 34

What is the osmolality of heathy eyes?

Answer 34

~302mmol/kg

Question 35

What is the effect of hypotonic solutions on the eye?

Answer 35

Increases corneal epithelial permeability causing oedema

Question 36

What is the effect of hypertonic solutions on the eye?

Answer 36

Dehydration of the corneal epithelium

Question 37

What is the pH range that eyes can tolerate?

Answer 37

3.5-9

Question 38

What is the pH range of tears?

Answer 38

6.9-7.5

Question 39

What pH should ocular drugs be?

Answer 39

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

Question 40

What is the surface tension of healthy tear fluid?

Answer 40

43.6-46.6 mN/m

Question 41

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

Answer 41

- They destabilise the tear film

Question 42

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

Answer 42

- To prolong drug retention in the tear film - Enhances drug absorption - Reduces drainage rate of the drug

Question 43

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

Answer 43

- 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

Question 44

What are the advantages of eye solutions? (5)

Answer 44

- Easy to manufacture - Lowest cost of production - Relatively easy to administer - Rapid onset of action - Good dose uniformity

Question 45

What are the disadvantages to eye solutions? (2)

Answer 45

- Rapidly drained from the eye - Rate of drainage is proportional to the size of the drop

Question 46

What are the downsides to ocular suspensions? (4)

Answer 46

- 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

Question 47

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

Answer 47

Increase viscosity

Question 48

What are advantages of ocular gels? (2)

Answer 48

- Lower frequency of application than solutions - Can be activated to undergo phase transition in the eye

Question 49

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

Answer 49

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

Question 50

What are Punctal plugs?

Answer 50

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

Question 51

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

Answer 51

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

Question 52

What is Sensimed triggerfish?

Answer 52

It is a contact lens which continuously measures interocular pressure.