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Mathew Kurian Kummelil, Rohit Shetty, Abhijit Sinha Roy, Purnima R Srivatsa, Rudy M Nuijts; Corneal biomechanical properties as a predictor of surgically induced astigmatism during cataract surgery. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3723.
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To study the correlation between the surgically induced astigmatism during uncomplicated phacoemulsification and the preoperative biomechanical properties of the cornea.
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 cataract evaluation and uneventful phacoemulsification using a standardized surgical technique. Specific for this study were pre-op corneal biomechanics measured using a Scheimpflug device and topography pre and 6 weeks post-operatively. The outcome measures were the surgically induced astigmatism calculated by vector analysis and its correlation with the corneal biomechanics.
44 eyes of 44 patients with a mean age of 62.11 ± 8.94 years were included in the study. 24 were males and 25 were right eyes. Mean UDVA improved from 1.15 ± 0.93 to 0.26 ± 0.23 (p<0.001) while the CDVA improved from 0.78 ± 0.93 to 0.10 ± 0.13 (p<0.001) postoperatively. The mean baseline IOP was 14.76 ± 3.00 mmHg, pachymetry was 524.59 ± 42.60 microns, IOL power was 20.32 ± 1.97 D and deflection amplitude was 1.09 ± 0.12 mm. Mean preoperative astigmatism of 0.73 ± 0.57 D had changed to 0.80 ± 0.52 D (p=2.03) as a result of the mean surgically induced astigmatism of 0.79 ± 0.73 D at 133.56 ± 32.91 degrees. The axis of the surgically induced astigmatism vector was significantly correlated with the deflection amplitude (p=0.032) while the magnitude of the vector was significantly correlated with the dioptric value of the preoperative steep axis (p=0.034).
The current understanding of the surgically induced astigmatism is based on static measures of the cornea 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 demonstrates the correlation of the axis of the surgically induced astigmatism vector with the deflection amplitude. Further prospective studies will help to improve the ability to accurately predict of the surgically induced astigmatism.
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