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Flashcards in Ocular Route Deck (21)
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1

Ocular route is..

administration via the eye

2

what does the pre-corneal tear film do?

lubricates and protects the eye surface

3

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

4

pH of normal tears is...

Diseased..

7.3-7.7


diseases - 5.2 - 9.3

5

pH of tears upon awakening?

lowest

6

Who has more acidic tears?
More alkaline?

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

alkaline in case of diseases such as dry eye

7

Human tear volume..

5-9uL

8

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

25-30uL

9

Basal tear are secreted at...

1.2 uL per minute

10

What is blinking?

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.

11

Blink rate in humans at rest..

17 per minute

12

Delivery can be via (3)

cornea - main route

periocular
passing the conjunctival and corneal epithelium

intravitreal
directly reach the back of the eye

13

Barriers to ocular local delivery: (3)

tear system constantly washed the eye

blinking promotes fluid clearence

maximum dose volume 20-30uL

14

Ophthalmic preparations include... (4)

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

15

Formulation considerations
Sterility

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

16

Formulation considerations
Tonicity

salt concentration within the lacrimal fluid determines its osmolarity

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

17

Formulation considerations
pH

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

18

Formulation considerations
Surface Tension

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

19

Formulation considerations
Viscosity

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

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

20

Eye drops must be:

easy to use

rapid onset of action

close to neutral pH, stable, sterile, particle free

21

Elimination routes

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.