Differences in Bioavailability of Fornixes in Different Head Positions

Abstract

Clinically, in infectious corneal or scleral ulcers, we have found some upper lesions to show a poorer response to eye-drops than lower lesions. This clinical observation stimulated our interest to investigate the differences of drug bioavailability in upper and lower fornixes in three different head positions. Seventeen people, 34 eyes, were enrolled in this study. There were three head positions for 0.1% fluorescein eye-drops application, including sitting, supine, and supine-with-chin-up. Schirmer's test paper was placed in the fornix to absorb the fluorescein, and the bioavailability was analyzed by fluorescence spectrophotometry. Fluorescein bioavailability of upper-and-lower fornixes were 1.30 × 10^-5% and 7.33 × 10^-5%, 3.93 × 10^-5% and 9.57 × 10^-5%, and 23.19 × 10^-5% and 5.09 × 10^-5% in sitting, supine, and supine-with-chin-up positions, respectively. Bioavailability of the lower fornix was significantly higher than that of the upper in the sitting position, and the bioavailability of the upper fornix was significantly higher than for the lower fornix in the supine-with-chin-up position. The bioavailability of the upper fornix in the supine-with-chin-up position was significantly higher than that in the sitting and supine positions, respectively. The total fluorescein bioavailability of both fornixes in the supine-with-chin-up position was significantly higher than that in the sitting position. We postulate that different head positions can influence drug bioavailability in the upper and lower fornixes. Ocular surface lesions in different sites may require different head positions during eye-drop application to obtain the best therapeutic results.