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- Title
Corneal epithelial permeability to fluorescein in humans by a multi-drop method.
- Authors
Srinivas, Sangly P.; Goyal, Arushi; Talele, Deepti P.; Mahadik, Sanjay; Sudhir, Rachapalle Reddi; Murthy, P. Pavani; Ranganath, Sudhir; Kompella, Uday B.; Padmanabhan, Prema
- Abstract
Purpose: The permeability of the corneal epithelium to fluorescein Pdc is an indicator of the health of the ocular surface. It can be measured in a clinical setting by determining the accumulation of fluorescein in the stroma following administration of the dye on the ocular surface. Here we demonstrate a new multi-drop method for the measurement of Pdc by a spot fluorometer. Methods: Twenty-nine healthy participants were recruited for this study. First, a probe-drop of fluorescein (0.35%, 2 μL) was instilled on the conjunctiva. The clearance of the dye from the tears was immediately measured using the fluorometer. Following this, two loading drops (2%; 6 μL each) were administered 10 min apart. Fifteen minutes later, the ocular surface was washed and fluorescence from the stroma Fs was measured. Permeability was calculated using Pdc = (Q x Fs)/ (2 x AUC), where Q is the stromal thickness and AUC is the area under the fluorescence vs. time curve for the loading drops. Results: After the probe drop, the tear fluorescence followed an exponential decay (elimination rate constant; kd = 0.41 ± 0.28 per min; 49 eyes of 29 subjects), but the increase in Fs was negligible. However, after the loading drops, the measured Fs was ~ 20-fold higher than the autofluorescence and could be recorded at a high signal to noise ratio (SNR > 40). The intra-subject variability of kd was insignificant. Since fluorescein undergoes concentration quenching at > 0.5%, the value of AUC for the loading drops was estimated by scaling the AUC of the probe drop. The calculated Pdc was 0.54 ± 0.54 nm/sec (n = 49). A Monte Carlo simulation of the model for the multi-drop protocol confirmed the robustness of the estimated Pdc. Conclusions: The new multi-drop method can be used in place of the single-drop approach. It can overcome a lack of sensitivity in fluorometers of high axial resolution. The Pdc estimated by the multi-drop method is ~ 11-fold higher than previously reported but closer to the value reported for other drugs with equivalent octanol/water partition coefficient.
- Subjects
CORNEA physiology; EPITHELIUM; FLUORESCEIN; RADIOACTIVE decay; PERMEABILITY
- Publication
PLoS ONE, 2018, Vol 13, Issue 6, p1
- ISSN
1932-6203
- Publication type
Article
- DOI
10.1371/journal.pone.0198831