Biomechanical changes in the cornea following cataract surgery: A prospective assessment with the Corneal Visualisation Scheimpflug Technology

Abstract

Importance: Intraocular pressure (IOP) is often reduced following cataract surgery. Postoperative changes in corneal stiffness are likely to be at least partly responsible for any reduction in IOP measured with applanation tonometry.

Background: To determine the effect of cataract surgery and corneal incision size on corneal biomechanics.

Design: Prospective randomized trial.

Participants: One hundred prospectively enrolled patients qualifying for cataract surgery.

Methods: Participants were randomized to clear corneal incisions with a 2.20 or 2.85 mm keratome. Corneal Visualisation Scheimpflug Technology (Corvis-ST) tonometry and dynamic corneal response measurements were obtained preoperatively, and 3 mo postoperatively. Multiple regression analysis was completed using R software.

Main outcome measures: Corvis-ST biomechanical parameters.

Results: Ninety-three eyes of 93 patients were included in the final analysis. Mean Corvis-ST biomechanically corrected IOP decreased by 3.63 mmHg postoperatively (95% confidence interval = 2.97-4.35, P ≤ 0.01), and central pachymetry increased by 6.96 μm (4.33-9.59, P ≤ 0.01). Independent of IOP and pachymetry changes, mean (±SE) corneal first applanation stiffness parameter reduced by 9.761 ± 3.729 (P = 0.01) postoperatively. First applanation velocity increased by 0.007 ± 0.002 ms, second applanation velocity increased by 0.012 ± 0.004 ms (P ≤ 0.01), the first applanation deformation amplitude increased by 0.008 ± 0.002 mm (P ≤ 0.01) and the deflection amplitude at highest concavity increased by 0.030 ± 0.069 (P ≤ 0.01). There were no significant differences between different incision size groups.

Conclusions and relevance: Corneal stiffness is reduced 3 mo following cataract surgery and is associated with falsely low IOP measurements. This finding may be important for glaucoma patients and in particular when assessing the effectivity of minimally invasive glaucoma surgery devices.

Keywords: Corneal Visualisation Scheimpflug Technology; cataract surgery; corneal biomechanics.