Ocular Delivery Flashcards
What is the anterior segment of the eye?
Front
What is the posterior segment of the eye?
Back
What is the eye volume?
7 µL
What are usual eyedrops doses?
20 to 50 µL
Why is there limited uptake of eyedrops?
Tear dilution
Short acting
Limited volume of the eye
What percentage of eyedrops are usually absorbed?
6.5%
How are posterior segment diseases treated?
Intravetreal injection
What eye condition would intavetrial injections be used for?
Age Related macular degeneration (avastin)
What are periocular injections?
Subconjunctival
Subtenon
Peribublar
Retrobublar
What are the routes can be used to treat eye conditions?
Parental – blood aqueous barrier and blood retinal barrier overcome
Oral – limited accessibility to many targeted ocular tissues
What are the six static ocular barriers?
Cornea
Sclera
Tear film
Conjunctiva
Vitreos humour
Retina
How does the cornea act as a barrier?
It is the outermost transparent layer
Drugs need to be negatively charged but anti-microbials positively charged
How does the sclera act as a ocular barrier?
It is structurally supportive
Drug moves through holes in matrix
The matrix is made from mucopolysaccharides and collagen
What gland releases tears and how they spread?
Lacrimal gland
Spread via blinking creating a tear film
How thick is the tear film and what is its pH?
7 µm thick
PH 7.3 to 7.7
What is the role of the tear film?
Remove material from surface of eye (drugs)
What layers make up the tear film?
External lipid layer
Middle aqueous layer
Adherent mucus layer
what is the surface area of the conjunctiva
18 cm²
What is the function of the conjunctiva?
Help form and maintain pre-corneal tear film
How does the conjunctiva act as a barrier?
It has tight junctions
What is the function of the virtuous humour?
Shape support of retina and lens
How does the retina act as a barrier?
The blood retina barrier
Drugs enter choroid but struggle in the retina
What are other barriers to ocular delivery other than static barriers?
Dynamic ocular – blood and lymphatic system
Metabolic ocular and eflux pumps
What are three types of ocular implants?
Subconjunctival implant – for anterior segment disease
Intrasceral- both anterior and posterior
Intravetreal- posterior
What drug does Ocusert deliver, for how long and for what condition?
Pilocarpine, one week, glaucoma
How does Ocusert treat glaucoma ?
Increases aqueous humour outflow, decreasing intra ocular pressure
What kinetics does Ocusert follow?
Zero order kinetics, membrane permeation control and depends on excess drug in reservoir
What is the mechanism of Ocusert?
Water enters through ethylene membrane, dissolves drug
What are the advantages of Ocusert?
Reduced installations of eyedrops
What are two other examples of non-biodegradable ocular implants?
Vitrasert- aids Related retinitis. Attached to sclera- side effect is retinal detachment
Retisert- prevents blindness. 30 month delivery ,smaller so smaller incision.
What are disadvantages of non-biodegradable implants?
Large incisions
Need expert
Cost
Need surchers, or other anchors
Need re-implantation once drug completely released
Side effects include retinal detachment and cataracts
What are examples of biodegradable ocular implants?
Lacrisert- Made of HPC, treats dry eye by stabilising and thickening the pre-corneal tear film- prolongs tear break up time. Side effects include blurred vision and irritation.
Ozurdex- Dexamethasone for macular Odema, intro, PLGA matrix. Six month delivery.
