Ocular Route

Question 1

Ocular route is..

Answer 1

administration via the eye

Question 2

what does the pre-corneal tear film do?

Answer 2

lubricates and protects the eye surface

Question 3

the pre-corneal tear film consists of what layers? (3)

Answer 3

superficial lipid layer
- sterol esters, wax esters and fatty acids to reduce evaporation rate of tears

central aqueous layer
- electrocytes, proteins, biopolymers, urea

inner mucus layer
- allows spread of tear film over the eye surface on blinking

Question 4

pH of normal tears is…

Diseased..

Answer 4

7.3-7.7

diseases - 5.2 - 9.3

Question 5

pH of tears upon awakening?

Answer 5

lowest

Question 6

Who has more acidic tears?

More alkaline?

Answer 6

contact-lens wearers more acidic due to impediment of the efflux of co2

alkaline in case of diseases such as dry eye

Question 7

Human tear volume..

Answer 7

5-9uL

Question 8

Maximum amount of fluid that can be held in lower eyelid sack..

Answer 8

25-30uL

Question 9

Basal tear are secreted at…

Answer 9

1.2 uL per minute

Question 10

What is blinking?

Answer 10

An important defence mechanism of the eye.

Essential for periodic reforming of the tear film.

Activates a pumping mechanism for the drainage of tears through the lacrimal drainage apparatus.

Question 11

Blink rate in humans at rest..

Answer 11

17 per minute

Question 12

Delivery can be via (3)

Answer 12

cornea - main route

periocular
passing the conjunctival and corneal epithelium

intravitreal
directly reach the back of the eye

Question 13

Barriers to ocular local delivery: (3)

Answer 13

tear system constantly washed the eye

blinking promotes fluid clearence

maximum dose volume 20-30uL

Question 14

Ophthalmic preparations include… (4)

Answer 14

solutions
simple design, cheap, homogenous dose between 25 to 50 uL

ointments
reduce clearing, may cause blurring. used for poorly soluble drugs, hydrophobic and hydrophilic

gels
semi-solid, water soluble base so more suitable than ointments for water soluble drugs

ion-exchange resins
drug is ionically bound to an ion-exchange resin to form an insoluble complex. released through exchange of drug ions with ions in tear fluids

Question 15

Formulation considerations

Sterility

Answer 15

must be sterile or infections could lead to vision loss

preservatives must be included in multi-dose containers to inhibit microbial growth e.g. benzalkonium chloride

single dose units developed

Question 16

Formulation considerations

Tonicity

Answer 16

salt concentration within the lacrimal fluid determines its osmolarity

hypotonic cause oedemaa
hypertonic cause dehydration
= both cause irritation and induce tear production

Question 17

Formulation considerations

pH

Answer 17

pH range of 3.5 to 9, extreme pH could damage ocular tissue

Question 18

Formulation considerations

Surface Tension

Answer 18

surfactants included to solubilise or disperse drugs and decrease irritation portenial

lower surface tension can destabilise the tear film and disperse the lipid layer into droplets

Question 19

Formulation considerations

Viscosity

Answer 19

increasing viscosity of solutions can prolong their residence time thus enhance drug absorption

over the viscosity limit (0.9N) would cause pain / cause blurring.

Question 20

Eye drops must be:

Answer 20

easy to use

rapid onset of action

close to neutral pH, stable, sterile, particle free

Question 21

Elimination routes

Answer 21

from aqueous humour into systemic uveoscleral circulation

outflow through trabecular meshwork and Schlemm’s canal

from vitreous humour via diffusion into anterior chamber

via posterior route across blood retinal barrier.