ABSTRACT
PURPOSE: To assess the effect of a combination of proparacaine 0.50%-sodium fluorescein 0.25% and ultrasound (US) pachymetry on central and midperipheral corneal thickness. SETTING: School of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom. DESIGN: Case series. METHOD: Topographic measurements of corneal thickness in healthy right eyes were obtained using a scanning-slit device (Orbscan IIz) and a Scheimpflug device (Pentacam) before and after application of proparacaine 0.50%-sodium fluorescein 0.25% and US pachymetry. Changes in corneal thickness in the center and 2.5 mm from the center in the temporal, nasal, inferior, and superior locations were assessed. RESULTS: The study evaluated 35 eyes. The scanning-slit and Scheimpflug devices recorded a small but statistically significant increase in corneal thickness at all locations (mean 4.9 ± 14.3 [SD] to 9.1 ± 11.7 µm; P<.05, paired t test). The cornea swelled uniformly across its diameter (scanning slit, P=.934; Scheimpflug, P=.654; analysis of variance); there was no statistically significant difference in the amount of swelling between the 2 devices (P>.05, t test). The 95% limits of agreement were broad (-10 to +30 µm), suggesting a large degree of interindividual variability. CONCLUSIONS: Ultrasound pachymetry combined with proparacaine 0.50%-sodium fluorescein 0.25% caused a small (<10 µm) but significant amount of corneal swelling on average. Because the effect on corneal thickness may be greater than -10 to +30 µm in individual cases, clinicians should avoid contact procedures before obtaining topographic maps of corneal thickness using scanning-slit and Scheimpflug devices.
