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Tear Clearance Rate Assessment with a Modified Slit Lamp Biomicroscope
1Visual Optics Group, Cathedral of Optics and Photonics, Department of Fundamental Problems of Technology, Wroclaw University of Science and Technology, Wrocław, Poland. Izabela.garaszczuk@pwr.edu.pl.
Purpose:
Tear clearance rate (TCR) was assessed historically with fluorophotometry and used as a marker of dry eye disease (DED). Since it requires advanced tools and specialised expertise, this method has largely been confined to research settings. This study proposed a clinically accessible method for assessing TCR using a modified slit lamp biomicroscope.
Methods:
This cross-sectional study included 95 subjects divided into dry eye (n = 65) and age-matched control (n = 30) groups. Five microlitres of 0.5% fluorescein solution was instilled, and tear fluorescence intensity decay was recorded over 5 min post instillation using a smartphone attached to a slit lamp biomicroscope, equipped with narrow-band filters designed to observe fluorescence. Custom-written software was used to quantify fluorescence intensity over time from the entire exposed ocular surface and calculate blinking frequency. TCR was calculated as the percentage drop in image intensity at selected intervals (0, 0.5, 1, 2, 3, 4 and 5 min) post instillation. Additionally, subjects underwent symptom assessment (ocular surface disease index (OSDI) and 5-item dry eye questionnaire (DEQ-5)), tear osmolarity, ocular surface staining, tear meniscus height, bulbar and limbal redness and noninvasive tear film break-up time (NIKBUT) assessment with the Oculus Keratograph 5M.
Results:
Biomicroscope-based TCRs were lower in the DED group than controls, with TCR₀.₅₋₂ (percentage decrease in fluorescence intensity between 30 s and 2 min after instillation) showing the strongest discriminatory capacity between these two groups (TCR₀.₅₋₂: 6.9% vs. 13.8%, p < 0.01). Early-phase TCRs correlated linearly with DED severity, OSDI, DEQ-5 and ocular surface staining (r from -0.21 to -0.43, all p < 0.05) and positively with measures of NIKBUT (r from 0.27 to 0.30, all p < 0.01).
Conclusions:
This study demonstrated the clinical feasibility of assessing TCR using a modified slit lamp biomicroscope. The method discriminates effectively between non-DED and DED subjects, with strong correlations with established diagnostic parameters.
