Intra-observer repeatability assessment of the S390L Firefly WDR slit lamp in patients with dry eye disease: Objective, automated and non-invasive measures

Abstract

Objectives: To assess the intra-observer repeatability of automated, objective and non-invasive measures obtained with the S390L Firefly WDR slit lamp. Methods: This cross-sectional study included fifty eyes of patients with dry eye disease (DED) with a mean age of 55.06 ± 12.96 years. Three consecutively repeated measures of the following variables were obtained: first non-invasive break-up time (F-NIBUT), average non-invasive break-up time (A-NIBUT), tear meniscus height (TMH), tear meniscus area (TMA), nasal ciliary hyperemia (NCIH), temporal ciliary hyperemia (TCIH), nasal conjunctival hyperemia (NCOH), temporal conjunctival hyperemia (TCOH), upper loss area meibomian gland (U-LAMG), lower loss area meibomian gland (L-LAMG), upper meibomian gland dysfunction grade (U-MGD grade) and lower meibomian gland dysfunction grade (L-MGD grade). Intra-observer repeatability was estimated with coefficient of variation (CoV), intra-subject standard deviation (Sw) and Bland-Altman plots. Results: All variables showed no statistically significant differences in the repeated measures analysis except for L-MGD grade (P = 0.045). F-NIBUT and A-NIBUT obtained the highest CoV with an average value of 0.48 ± 0.41 [0.02 to 1.00] and 0.34 ± 0.25 [0.02 to 1.00], respectively. The remaining variables showed CoVs between 0.04 ± 0.11 [0.00 to 0.43] and 0.18 ± 0.16 [0.00 to 0.75]. A-NIBUT, TMA, NCOH and L-LAMG obtained a Sw of 2.78 s, 0.21 mm2, <0.001 and 4.11 %, respectively. Bland-Altman plots showed a high level of agreement between pairs of repeated measures. Conclusion: The S390L Firefly WDR slit lamp has moderate intra-observer repeatability for F-NIBUT and A-NIBUT, which suggests that they are tests with high variability. The remaining variables show satisfactory intra-observer repeatability.