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Sangly P Srinivas, Hadiya Farhath Pattan, Nandini Ravi, Prema Padmanabhan, Pete S Kollbaum, Rachapalle Reddi Sudhir; Ocular surface kinetics of topical fluorescein in Systane Gel. Invest. Ophthalmol. Vis. Sci. 2021;62(8):1326.
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To determine the Systane gel (SG) effect on the ocular surface kinetics of fluorescein using a custom-made spot fluorometer.
Experiments were performed with a cohort of healthy subjects with no ocular disease. Informed consent was obtained from all subjects before measurements. Fluorescein (0.5%), formulated in normal saline or SG, was administered as a 30 µL drop into the lower cul-de-sac. The patients were asked to blink after the drop, and corneal surface fluorescence measurements were begun immediately using a custom-made spot fluorometer. The fluorometer, built to measure fluorescence from any spot in the anterior segment, can record fluorescence at > 1 kHz. The fluorescence measurements, which could be started typically in < 10 seconds after the drop, were continued until baseline levels were observed. The measurements were performed frequently after the drop's administration but at 1-2 samples/min at the later stages. The dynamics of tear fluorescence was fitted to monoexponential decay to determine the elimination rate constant (expressed as half-life) and fluorescence at t = 0 (expressed in mV; i.e., initial concentration of fluorescein in tears). The tear meniscus height (TMH) and tear breakup time (TBUT) were also assessed after administration of the drops with a keratograph (Oculus 5M) every 20 mins for 1 hour.
After administration of fluorescein in NS or SG, the tear fluorescence decayed with a single exponential profile. The half-life of tear fluorescence and the fluorescence at zero time after an SG drop were much higher than those with NS (n = 8; p < 0.05). Fig. 1 shows tear fluorescence vs. time in one subject following SG and NS drops. Although fluorescence vanished from the ocular surface by ~ 20 min (with SG), the mucoadhesive property of SG lasted longer. This was apparent by the keratograph measurements, which showed an increase in TBUT for more than 40 min after an SG drop (p < 0.05). NS did increase TBUT significantly, even at 20 min.
The increase in half-life with SG is consistent with increased tear film stability noted with the agent [1-2]. Thus, the half-life of fluorescein on the ocular surface is a measure of the potential efficacy of SG in the artificial tear substitutes employed in the palliative treatment of DED. In conclusion, we have demonstrated a paradigm to assess formulations of artificial tear substitutes for DED with our new custom-made fluorometer.
This is a 2021 ARVO Annual Meeting abstract.
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