A Laser Scanning Confocal Raman Spectroscopy (LSCRS) system was applied for
the non-invasive quantification of the transport of a drug through the rab
bit cornea in vivo.
Employing LSCRS, the changes in the amplitude of a drug-specific Raman sign
al were assessed over time in the tearfilm and corneal epithelium of the li
ving rabbit eye (n=6), after topical application of 25 mu L Trusopt 2%(TM).
This allowed for quantification of pharmacokinetic variables. The effect o
f the drug on corneal hydration was also monitored.
LSCRS demonstrated adequate sensitivity and reproducibility, for continuous
peal-time monitoring of the Trusopt concentration. Each concentration-time
curve had a bi-phasic trend; the rapid initial phase (t<8 min.) correspond
s to the nonproductive losses of Trusopt from the tears (k(10)=0.24+/-0.04
min(-1)), and the slower later phase (t>20 min.) is the result of transfer
of the drug from the corneal epithelium to the stroma (k(23)=0.0047+/-0.000
4 min(-1)). Drug absorption into the corneal epithelium occurred at a rate
of k(12)=0.034+/-0.006 min(-1). Trusopt caused an acute dehydrating effect,
with a maximum decrease in corneal hydration of similar to 15% at similar
to 60 min, following application of the drug.
LSCRS has the specificity, sensitivity, reproducibility and spatial resolut
ion for employment as a potentially valuable tool for the study of ocular p
harmacokinetics.