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.

Comparison of Ectasia Detection in Early Keratoconus Using Scheimpflug-Based Corneal Tomography and Biomechanical Assessments

“…20 A notable limitation of the Corvis ST in the screening of keratoconus is that it automatically images a single, central 8.5-mm horizontal section of the cornea. 5,11 Given that a common location of focal thinning in keratoconus is inferotemporally, the Corvis ST may therefore fail to capture the focal area of corneal biomechanical compromise in keratoconus. 4,21 In addition, the sensitivity of the Corvis ST in assessing the subtleties in corneal biomechanical properties may be inadequate to detect early keratoconus.…”

“…1,[5][6][7][8][9][10] The Corneal Visualization Scheimpflug Technology (Corvis ST; OCULUS Optikgeräte GmbH, Wetzlar, Germany) is a recently developed noncontact tonometry system. 6,11 The Corvis ST used a 60-mm Hg, 3.05-mm diameter collimated air pulse to deform the cornea while dynamically capturing the resulting corneal curvature changes in space and time using a high-speed Scheimpflug camera at a rate of frames per second. 11 The measurement of this dynamic corneal response allows the description of corneal biomechanics using parameters such as applanation times, velocities, and deflection amplitudes.…”

Corneal Biomechanical Parameters after 60-Year-Old

“… 7 8 9 10 11 Cataract surgery affects the biomechanical properties of the cornea. 12 13 14 15 The viscoelastic properties of the cornea change in the elderly population due to connective tissue changes with age. 16…”

Experimental Assessment of the Spatial and Temporal Distribu-Tion of Non-contact Tonometer Airflows

“…Through the use of this data and empirically derived algorithms, the device is able to offer measures of corneal hysteresis and corneal resistance factors that can be considered with the intraocular pressure measurements. [2] Despite significant efforts to understand corneal biomechanics with the use of the CorvisST and ORA [6][7][8][9][10][11][12][13][14][15][16], there is a dearth of literature on the actual physical and geometric properties of the airflow pressure applied to the cornea with these devices. Indeed, the physical attributes of the air-pressure applied during non-contact tonometry is fundamental to the measures of both intraocular pressure and corneal biomechanics.…”