ocular drug delivery

Question 1

what are the different layers of the eyes

Answer 1

outer - sclera and cornea
middle- iris, ciliary body and choroid
inner - retina
chambers - anterior and posterior, vitreous cavity

Question 2

what are the barriers to topical ocular ddel

Answer 2

pre-corneal factors
- solution drainage, blinking, tear film, tear turnover
- induced lacrimation
- mucin in tear film is hydrophobic
anatomical
- layers of cornea, conjunctiva and sclera

Question 3

what are the barriers to systemic ocular ddel

Answer 3

blood aqueous barrier
blood retinal barrier

Question 4

why is the blood retinal barrier a barrier to systemic ocular ddel

Answer 4

requires specific targeting systems, limited access requires high oral doses

Question 5

what considerations need to be made when developing drugs for ocular delivery

Answer 5

osmolarity
pH
surface tension
viscosity

Question 6

why does osmolarity need to be considered when developing drugs for ocular delivery

Answer 6

determined by concentration of lacrimal fluids - 0.9-1%
hypotonic cause oedema, hypertonic dry the corneal epithelium

Question 7

why does pH need to be considered when developing drugs for ocular delivery

Answer 7

important in controlling ionisation and corneal permeability (6.9-7.5)

Question 8

why does surface tension need to be considered when developing drugs for ocular delivery

Answer 8

drops that lower the surface tension of the eye
- destabilise tear film
- disperse lipids into droplets
- solubilised by drug/surfactants in formulation

Question 9

why does viscosity need to be considered when developing drugs for ocular delivery

Answer 9

to prolong retention in tear film
PVP, PVA, MC, HPMC
blinking force limits viscosity

Question 10

what are the advantages and disadvantages of using solutions for topical ocular ddel

Answer 10

easy and cheap
rapid onset of action with good dose uniformity
rapidly drained from the eye - proportional to drop size
variations in amount dispensed

Question 11

why are suspensions used for ocular ddel

Answer 11

administration of soluble aqueous drugs - steroids and to prolong release

Question 12

why are gels used in ocular ddel

Answer 12

semi-solid with water soluble base - polymers dispersed in liquids
can be activated to undergo phase transition in the eye

Question 13

what are the 3 routes of systemic/direct ocular ddel

Answer 13

intracameral - anterior chambers
intravitreal
periocular (subconjunctival, retrobulbar and peribulbar)

Question 14

what are the advantages and disadvantages of intravitreal injection for ocular ddel

Answer 14

 Distribution in vitreous is non-uniform – LMW can rapidly distribute, HMW cannot
 Best way to deliver but poor compliance
 Drug retention requires frequent administration

Question 15

what are punctual plugs

Answer 15

plugs inserted into tear ducts that release drugs over 1-2m

Question 16

what are the two types of implant for ocular ddel

Answer 16

• Fluocinolone over 3 yrs – non-bioerodible
• Latanoprost, subconjunctival space, 3m as is bioerodible

Question 17

what is iontophoresis and how is it used in ocular ddel

Answer 17

• The basic electrical principle that oppositely charged ions attract and same charged ions repel is the central tenet of iontophoresis.
• The ionized substances are driven into the tissue by electrorepulsion at either the anode (for positive drug) or the cathode (for negatively charged drug)
• ocular iontophoresis is capable of delivering substantially higher ocular drug concentrations than traditional topical applications, leading to greater bioavailability and more sustained therapeutic effect and reducing the frequency of dosing

Question 18

what are drug eluting contact lenses

Answer 18

drug coated on or imprinted on inner side of lenses – provides steady drug release

Question 19

what are topical ophthalmic drug delivery devices

Answer 19

• device floats on the sclera under eyelid
• 3-90 days of delivery
• Human clinical trials

Question 20

what is triggerfish

Answer 20

• Contact lens providing constant IOP readings
• Sensor contains strain gauges that measure corneal curvature changes caused by intraocular pressure variations