Impact of Small Incision Lenticule Extraction for High Myopia on Intraocular Pressure Measurements With Pneumotonometry

PURPOSE: To evaluate the medium-term impact of small incision lenticule extraction (SMILE) on air-puff tonometry (APT) and how it may be corrected. METHODS: In this controlled prospective study, 69 eyes from 69 patients treated with SMILE for high myopia (mean:-7.22 diopters) were included. Central corneal thickness (CCT), spherical equivalent refraction (SEQ), corneal power, and traocular pressure (IOP) (assessed by APT) were measured before and 3 months after surgery. RESULTS: The measured IOP decreased significantly after SMILE surgery (mean:-6.43 mm Hg), indicating a significant underestimation of the true IOP by APT. There was a significant correlation between change in SEQ, CCT, and apparent IOP. Correcting the apparent IOP measurement by applying a multiple regression correction did not provide significantly better estimates compared to adding 6.4 mm Hg to the measurement. CONCLUSIONS: This study showed that previous SMILE surgery should be considered when interpreting APT measurements, because the measurements underestimate the true IOP. Multiple regressions cannot estimate the true IOP with certainty. For screening purposes, adding 6.4 mm Hg to the apparent IOP of a patient treated for high myopia may be sufficient.