The Influence of the Dropsize on the Elimination of an Ophthalmic Solution from the Precorneal Area of Human Eyes

Abstract

In order to study the influence of the dropsize on the ocular contact time and on the drainage of a fluorescent tracer a non-invasive method, using a slit lamp fluorophotometer is employed. Quantitative measurements of the fluorescence decay in the tear film, after instillation of an iso-osmotic tracer solution ranging in volume from 20 to 1 μl, are performed.

In most cases an initial fast decay is followed by a slower elimination after a few minutes. The initial phase of the decay profile obeyes fairly well first order kinetics and the tear elimination coefficient is calculated. Important intra and inter subject variations are noted.

In contrast to results obtained with rabbits no linear relationship between dropsize and tear elimination coefficient is observed. The elimination coefficient is insensitive to the dropsize over the range of 1 to 10 μl and sometimes to 20 μl.

In general a dropsize smaller than 20 μl should be preferred to improve the therapeutic effect of ophthalmic drugs.