Flashcards in Ocular Route Deck (21)
Ocular route is..
administration via the eye
what does the pre-corneal tear film do?
lubricates and protects the eye surface
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
pH of normal tears is...
diseases - 5.2 - 9.3
pH of tears upon awakening?
Who has more acidic tears?
contact-lens wearers more acidic due to impediment of the efflux of co2
alkaline in case of diseases such as dry eye
Human tear volume..
Maximum amount of fluid that can be held in lower eyelid sack..
Basal tear are secreted at...
1.2 uL per minute
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.
Blink rate in humans at rest..
17 per minute
Delivery can be via (3)
cornea - main route
passing the conjunctival and corneal epithelium
directly reach the back of the eye
Barriers to ocular local delivery: (3)
tear system constantly washed the eye
blinking promotes fluid clearence
maximum dose volume 20-30uL
Ophthalmic preparations include... (4)
simple design, cheap, homogenous dose between 25 to 50 uL
reduce clearing, may cause blurring. used for poorly soluble drugs, hydrophobic and hydrophilic
semi-solid, water soluble base so more suitable than ointments for water soluble drugs
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
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
salt concentration within the lacrimal fluid determines its osmolarity
hypotonic cause oedemaa
hypertonic cause dehydration
= both cause irritation and induce tear production
pH range of 3.5 to 9, extreme pH could damage ocular tissue
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
increasing viscosity of solutions can prolong their residence time thus enhance drug absorption
over the viscosity limit (0.9N) would cause pain / cause blurring.
Eye drops must be:
easy to use
rapid onset of action
close to neutral pH, stable, sterile, particle free