Ophthalmology Flashcards
What are the different anterior eye diseases? How can they be treated?
blepharitis, styes
- hygiene, warm compresses, antibiotic eye drops
dry eyes
- artificial tears
conjunctivitis
- artificial tears, antihistamines (allergic), antibiotics
cataract
- surgery
glaucoma
- beta blockers, prostaglandin analogue
What are the different routes of ocular delivery?
transcorneal permeation
non-corneal permeation across conjunctiva and sclera
drug distribution from blood stream via blood aqueous barrier
elimination via aqueous humor turnover
elimination across blood- aqueous barrier
drug distribution across blood-retinal barrier
intravitreal drug administration
elimination across blood- retinal barrier
elimination via anterior route
What does the preocular area consists of?
tear film and nasolacrimal apparatus
What does the tear film consist of?
mucus layer
- secretes mucin to aid in uniform lubrication
- lowers surface tension and increase stability of the tear film
aqueous layer
- secretes tears from the lacrimal gland to lubricate the ocular surface and wash away contaminations
lipid/oily layer
- produced by meibomian glands to minimise tear evaporation and counteract tear overflow
What does the nasolacrimal drainage apparatus do?
lacrimal gland secretes tears that leave through excretory ducts
tears travels to the punctum (upper and lower) and drain through to the throat then the GIT
- removes excess tears
What is the effect of nasolacrimal obstruction?
nasolacrimal obstruction
- increases bioavailability as blockage stops loss of ocular drugs
= increases retention and prevents wash out of drugs
What do the ocular membranes consist of?
conjunctiva
cornea
sclera
are the routes of absorption
What is the conjunctiva? What is its function?
mucous membrane lining the ocular surface (excluding the cornea) as well as the inner eyelid
function
- mucus production by goblet cells
- anchoring the pre corneal tear film
- fighting infections
What is the cornea? What is its function?
optically transparent tissue that acts as the principal refractive element of the eye
What is the sclera?
the white of the eye which is covered by the conjunctiva
- area of absorption of large and hydrophilic drug molecules
What are the advantages of topical treatments vs systemic treatments?
topical
- less undesirable systemic side effects
- more convenient and simple method of delivery
- overcomes hepatic first pass metabolism
systemic
- very high systemic doses must be administered
What are the disadvantages of topical treatments?
very rapid and extensive drug loss caused by drainage and high tear fluid turnover
corneal impermeability
- is a barrier
pulse entry
non-specific absorption
- systemic side effects
ocular metabolism
- enzymatic activity
What are formulation strategies to improve ocular drug absorption/opthalmic drug delivery?
increasing corneal permeability
prolongation of the drug residence time in the pre corneal area
slowing drug release from the delivery system thus avoiding pulse entry
What factors need to be considered when designing topical ocular delivery systems?
physicochemical properties of the drug or bioactive molecule
formulation additives
buffer capacity and pH
instillation volume (drop size)
osmotic pressure (tonicity)
clarity
biocompatibility (none irritant)
How can corneal permeability be increased?
by chemical and pharmaceutical modification
- using prodrugs
- using penetration enhancers = surfactants, bile salts, fatty acids, ion pairs and cyclodextrin
How can preocular retention be improved?
using
- viscous vehicles
- bioadhesive vehicles
- in situ activated gelling systems
using coarse, dispersed and colloidal systems
- suspensions and emulsions
- ointments and gels
- microemulsions, SEDDS and SMEDDS
- liposomes
- particulate systems
What is the purpose of preservatives in eye solutions? What are different examples?
prevent the growth of bacteria after opening the bottle, allowing for longer periods of use
- lyse bacterial cell membranes and lyse corneal epithelium
benzalkonium chloride
What are the advantages and disadvantages of ointments?
advantages
- resistance to nasolacrimal drainage
- increased eye surface contact time
- resistance to dilution by tears
- method for formulating moisture sensitive
drugs
disadvantages
- interfere with vision
- may be associated with discomfort and ocular irritation
What are the disadvantages of suspensions compared to solutions?
suspensions must be shaken before use
- to redisperse drug solute in solvent
sterilisation is rewired
- may cause physical instability
particle size must be less than 10 microns
suspensions are expensive
What are the disadvantages of gels in comparison to solutions?
water soluble drugs are readily released from systems
- pulse entry
a marked increase in viscosity results in rapid elimination
- reflex blinking
blurred vision
matted eyelids
What are in situ gelling systems (gel forming eye drops)? What factors do they depend on?
polymers that undergo solution to gel phase transition upon change in a physicochemical parameter such as
- ionic strength
- temperature
- pH
- solvent exchange
What are the advantages of in situ gelling systems (gel forming eye drops)?
easy instillation in liquid form but increased residence time of the formulation on the ocular surface due to gelling (increase in viscosity)
What are posterior eye diseases?
degenerative
- age related macular generation (ARMD)
vascular
- diabetic retinopathy
- retinal vein/artery occlusion
inflammatory
- uveitis
infectious
- endophthalmitis
What are the different drug absorption routes for posterior eye diseases?
intravitreal
periocular
intracameral
topical
