Cataract surgery causes biomechanical alterations to the eye detectable by Corvis ST tonometry

Abstract

PurposeModern cataract surgery is generally considered to bring about modest and sustained intraocular pressure (IOP) reduction. However, the pathophysiological mechanism for this remains unclear. Moreover, a change in ocular biomechanical properties after surgery can affect the measurement of IOP. The aim of the study is to investigate ocular biomechanics, before and following cataract surgery, using Corvis ST tonometry (CST).Patients and methodsFifty-nine eyes of 59 patients with cataract were analyzed. IOP with Goldmann applanation tonometry (IOP-G), axial length, corneal curvature and CST parameters were measured before cataract surgery and, up to 3 months, following surgery. Since CST parameters are closely related to IOP-G, linear modeling was carried out to investigate whether there was a change in CST measurements following cataract surgery, adjusted for a change in IOP-G.ResultsIOP-G significantly decreased after surgery (mean±standard deviation: 11.8±3.1 mmHg) compared to pre-surgery (15.2±4.3 mmHg, P<0.001). Peak distance (the distance between the two surrounding peaks of the cornea at the highest concavity), maximum deformation amplitude (the movement of the corneal apex from the start of deformation to the highest concavity) and A1/A2 velocity (the corneal velocity during inward or outward movement) significantly increased after cataract surgery (P<0.05) while radius (the central curvature radius at the highest concavity) was significantly smaller following cataract surgery (P<0.05). Linear modeling supported many of these findings, suggesting that peak distance, maximum deformation amplitude and A2 velocity were increased, whereas A2 deformation amplitude and highest concavity time were decreased (after adjustment for IOP change), following cataract surgery.ConclusionCorneal biomechanical properties, as measured with CST, were observed to change significantly following cataract surgery.Trial registrationJapan Clinical Trials Registry UMIN000014370

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

“…The peripheral location of the relatively small corneal incisions is the likely reason that no significant changes were detected by the Corvis‐ST. This finding is consistent with similar results noted when assessing biomechanical changes induced by corneal‐scleral incisions …”

“…It is also relevant to highlight that the Corvis‐ST images the cornea in horizontal sections, and that the main incisions in the current study were all temporal, which may have affected the results. One previous study included both temporal corneal incisions (N = 22) and superior scleral/corneal incisions (N = 37) but performed no statistical analyses comparing these groups …”

“…Paired t tests with Holm‐Bonferroni corrections were used to assess the effect of cataract surgery on all corneal biomechanical parameters. Because Corvis‐ST parameters are affected by both IOP and other clinical factors, the confounding effects of these variables should be accounted for during analysis . Multiple linear regression was used to create models for each of the Corvis‐ST biomechanical parameters, taking into account IOP, pachymetry, age, gender and measurement time (pre‐ or postoperative).…”

“…Previous studies investigating corneal biomechanical changes following cataract surgery have been small and reported conflicting results at 3‐mo follow‐up . Studies with the Corvis‐ST have previously reported statistically significant changes in corneal deformation amplitude (DA), first applanation (A1) time, A1 and A2 velocities and peak distance .…”

“…7,8 Due to the in vivo nature of the measurements, many Corvis-ST parameters are also affected by IOP and recent investigations have attempted to identify which parameters strongly relate to corneal stiffness independently of IOP. [9][10][11] One of the recently released Corvis-ST parameters is the biomechanically corrected IOP (bIOP), which corrects the Corvis-ST reported IOP by accounting for central corneal thickness and age. 9,12,13 All other parameters had negligible effect on IOP and were therefore omitted from the algorithm.…”