Reliability of Aqueous Flare Measurements During Uveitis by a Spot Fluorometer.

Purpose: To evaluate the reliability of intensity of light scatter (ILS) for diagnosing mild-to-moderate uveitis, which is difficult to score by the subjective standardized uveitis nomenclature (SUN) grading. Methods: ILS (in millivolts) was measured in healthy subjects and uveitis patients by a custom-made Spot fluorometer. The reliability was assessed by noise analysis of the instrument using turbid samples and intra- and interobserver variabilities. Results: ILS increased with the severity of inflammation: healthy (0.1498 ± 0.0564) and SUN0 (0.1590 ± 0.0564) < SUN1+ (0.2050 ± 0.0887) < SUN2+ (0.4283 ± 0.1895). The increase in ILS was more significant between healthy and SUN1+ (P < 0.0001) compared to the difference between SUN0 and SUN1+ (P = 0.0006). The instrument noise was small (σ = 0.002). Intraobserver measurements revealed no variability (P > 0.98) between measurements and predicted repeatability coefficients of 0.0754, 0.0522, and 0.0532 in healthy, SUN0, and SUN1+, respectively. Interobserver measurements also showed no variability (P > 0.88) and predicted intraclass correlation coefficient > 0.63 in healthy and uveitis subjects. Conclusions: The fluorometer enables precise measurement of ILS with negligible instrument noise, and the measurements are unaffected by intra- and interobserver variabilities. However, the difference in mean ILS between SUN0 and SUN1+ is greater than the instrument noise and comparable to intra- and interobserver variabilities. Thus, ILS measurements are likely impacted by blinking, eye movements, and focusing jitter. The impact of these factors must be reduced before using the fluorometer to distinguish mild-to-moderate uveitis.

Ocular Spot Fluorometer Equipped With a Lock-In Amplifier for Measurement of Aqueous Flare.

PURPOSE: To evaluate a custom-made ocular fluorometer for detection of intensity of light scatter (ILS) from the anterior chamber (A/C) as an objective measure of aqueous flare. METHODS: The fluorometer, equipped with a lock-in amplifier, was employed in the scatter mode to detect ILS from A/C. Measurements were performed with two illumination slit widths of 0.5 and 0.25 mm. The axial resolution at these slit widths were 80 and 200 µm, respectively. Healthy and pseudophakic eyes, with grade 0 Standardization of Uveitis Nomenclature (SUN) score, were employed as control subjects. ILS was also recorded in a cohort of patients who had undergone phacoemulsification and showed grades 1+ or 2+ on postoperative days 1 and 4. RESULTS: The inter- and intraobserver variabilities in the measurement of ILS were not significant. In cataract patients, ILS was significantly higher on postoperative day 1 relative to healthy eyes. By day 4, ILS decreased significantly and was only marginally different from ILS in quiet pseudophakic eyes or healthy eyes. Eyes with higher SUN scores showed proportionately increased ILS. The receiver-operator characteristic analysis indicated no advantage in using the smaller slit width in discriminating ILS at different SUN scores although it provided higher axial resolution. CONCLUSIONS: The lock-in-based spot fluorometer is reliable for measurement of ILS with high precision and accuracy.The measured ILS correlates linearly with SUN scores and can be used to provide a higher granularity for recording aqueous flare. TRANSLATIONAL RELEVANCE: The instrument can be used in the clinical management of uveitis and drug development toward uveitis.