Effect of a proparacaine 0.50%–sodium fluorescein 0.25% mix and contact ultrasound pachymetry on central and midperipheral corneal thickness measured by noncontact optical pachymetry

PurposeTo assess the effect of a combination of proparacaine 0.50%–sodium fluorescein 0.25% and ultrasound (US) pachymetry on central and midperipheral corneal thickness.SettingSchool of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom.DesignCase series.MethodTopographic 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.ResultsThe 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.ConclusionsUltrasound 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.Financial DisclosureNo author has a financial or proprietary interest in any material or method mentioned.