Posters

Correlation of corneal biomechanics to the surgically-induced changes in corneal curvature

Poster Details

First Author: P.Srivatsa INDIA

Co Author(s):    M. Kurian Kummelil   R. Shetty   A. Sinha Roy   R. Nuijts   K. Shetty  

Abstract Details

Purpose:

To study the correlation between the surgically induced changes in corneal curvature following uncomplicated phacoemulsification with the preoperative biomechanical properties of the cornea.

Setting:

Tertiary eye care centre, Research and Post-graduate teaching Institute, Bangalore, India.

Methods:

The study was a prospective non-randomized case series. Consecutive patients reporting to the hospital for cataract surgery without coexisting ocular or systemic co-morbidity and signing the informed consent form were included in the study that was cleared by the institutional ethics review board and followed the tenets of the Helsinki Declaration. The patients underwent routine pre and post-operative cataract evaluation and uneventful phacoemulsification using a standardized surgical technique. Incision location, size and architecture were standardized for all patients. Specific for this study was, pre-operative corneal biomechanics measured using a Scheimpflug device (CorVis ST) and Corneal Tomography (Pentacam; Oculus, Wetzlar, Germany) measured pre and 6 weeks post- operatively. The outcome measures of the study were surgically induced changes in corneal curvature, measured in terms of Coupling Ratio (CR) and Surgically Induced Astigmatism (SIA) calculated by vector analysis and its correlation with the corneal biomechanics, measured in terms of Deformation Amplitude (DA) - i.e., maximum amplitude (in mm) of the applanation at the highest concavity.

Results:

Eighteen eyes of 18 patients (10 males; 8 females) with a mean age of 60.20 ± 7.25 years with a temporal clear corneal incision were included in the study. Mean Uncorrected Distance Visual Acuity (UDVA) improved from 1.10 ± 0.89 pre-operative to 0.32 ± 0.30 post-operative (p< 0.01), while the Best Corrected Distance Visual Acuity (CDVA) improved from 0.87 ± 0.99 preoperatively to 0.09 ± 0.10 postoperatively (p<0.01). The mean baseline IOP was 14.88 ± 2.74 mmHg, pachymetry was 530.35 ± 45.68 µ, IOL power was 20.10 ± 2.72 Diopters (D) and the DA was 0.99 ± 0.28mm. The mean CR was 0.92 ± 0.28 and SIA was 0.74 ± 0.46 D. The data was tested for normality, as the data was found not to be distributed normally, Non-parametric tests were used for statistical analysis. Correlation between Corneal Curvature Changes and Corneal biomechanics was tested using Spearman's Correlation Coefficient. It was found that CR positively correlated with DA (Spearman's rho = 0.71, p = 0.001, significant at the 0.01 level)

Conclusions:

The current understanding of the surgically induced astigmatism is based on static measures like the age of the patients, corneal thickness, architecture, length and number of incisions and does not account for the dynamic nature of the biomechanical properties of the cornea. This study shows that for surgical incisions that are standardized in location, size and architecture, the corneal biomechanics influences the magnitude of post-operative change in the corneal curvature. With equipment that help the surgeon measure the corneal biomechanical properties astigmatism management will in future be able to account for the dynamics of the patient's corneal biomechanics. FINANCIAL INTEREST: NONE