Journal d'ophtalmologie clinique et expérimentale
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Intraocular Pressure Measurement after Photorefractive Keratectomy : Does Contact Area Matter?

Vetrugno Michele, Maino Anna, Ferreri Paolo, Cardia Giuseppina, Trerotoli Paolo, Serio Gabriella and Sborgia Carlo

Background: Refractive laser surgery induces substantial changes in corneal structure, causing inaccurate intraocular pressure (IOP) readings. Pascal dynamic contour tonometry (PDCT) and Icare rebound tonometer (RBT) are two novel devices that do not depend on applanation to measure IOP. Purpose of this prospective study was to compare PDCT and rebound tonometry versus Goldmann tonometry (GAT) in a group of patients who underwent photorefractive keratectomy (PRK).
Methods: Central corneal thickness and IOP were measured in 54 eyes before and after PRK. All IOP measurements were taken by the same examiner, using PDCT, RBT and GAT in a randomised, masked fashion.
Results: After excimer laser surgery, PDCT measurements were higher than GAT (p<0.0001) and RBT (p=0.0012). Multiple linear regression analysis indicated that size of contact area was significant (b=-0.504; p<0.0001) while corneal thickness was not (b=0.003; p=0.169). Bland-Altman test showed that there was good agreement between RBT and PDCT (p=0.454), whereas GAT gave lower IOP values than both RBT (p=0.0103) and PDCT (p=0.0031).
Conclusion: PDCT and RBT are less dependent on iatrogenic corneal changes than GAT and this might be related to their small contact area. In order to minimise IOP underestimation after excimer laser surgery, the clinician should consider adopting non-applanation tonometers like RBT and PDCT as an alternative to GAT.