Falsely high rebound tonometry

Abstract

Background: Rebound tonometry (RBT) can be used to measure intraocular pressure (IOP) in children unable to tolerate measurement with applanation tonometry (AT) while awake. RBT readings are often 2-3 mm Hg higher than AT. We have experienced children with a repeatedly higher difference between RBT and AT measurements (≥6 mm Hg). The purpose of this study was to identify demographic and ocular characteristics that contribute to this artifactuous discrepancy.

Methods: The medical records of pediatric patients with IOP measured by RBT followed by AT within 6 months without intervening surgery or change in medical management were retrospectively reviewed to identify potential predictors of greater difference between RBT and AT readings.

Results: A total of 123 eyes of 65 patients were included. In patients with normal IOP (≤24 mm Hg), 18.5% had a ≥6 mm Hg difference between RBT and AT, with RBT being higher. Risk factors for this included presence of persistent fetal vasculature (PFV), increased corneal diameter, and higher initial RBT value (>20). In patients with elevated IOP (>24 mm Hg), 77% had ≥6 mm Hg difference, with larger corneal diameter being the sole predictor. Eyes were less likely to have significant RBT-AT difference if there was corneal opacity or iris abnormalities in eyes with elevated IOP (>24 mm Hg).

Conclusions: In some children, RBT readings are ≥ 6 mm Hg higher than AT readings. Caution should be taken when interpreting RBT values in patients with PFV, increased corneal diameter, and higher initial RBT values.