Prediction of Surgically Induced Astigmatism in Manual and Femtosecond Laser-assisted Clear Corneal Incisions

Purpose: To assess the surgically induced astigmatism with femtosecond laser-assisted and manual temporal clear corneal incisions and to evaluate the performance of a model for prediction of the surgically induced astigmatism based on the preoperative corneal astigmatism.

Methods: Clinical data of 104 right eyes and 104 left eyes undergoing cataract surgery, 52 with manual incisions and 52 with femtosecond laser-assisted incisions in each eye group, were extracted and revised retrospectively. In all cases, manual incisions were 2.2 mm width and femtosecond incisions were 2.5 mm width, both at temporal location. A predictive model of the surgically induced astigmatism was obtained by means of simple linear regression analyses.

Results: Mean surgically induced astigmatisms for right eyes were 0.14D@65 (manual) and 0.24D@92 (femtosecond) (p > 0.05) and for left eyes, 0.15D@101 (manual) and 0.19D@104 (femtosecond) (p > 0.05). The orthogonal components of the surgically induced astigmatism (X, Y) were significantly correlated (p < 0.05) with the preoperative orthogonal components of corneal astigmatism (X, Y) (r = -0.29 for X and r = -0.1 for Y). The preoperative astigmatism explained 8% of the variability of the X and 3% of the variability of Y. The postoperative corneal astigmatism prediction was not improved by the surgically induced astigmatism obtained from the model in comparison with the simple vector subtraction of the mean surgically induced astigmatism.

Conclusion: Temporal incisions induce similar astigmatism either for manual or for femtosecond procedures. This can be clinically negligible for being considered for toric intraocular lens calculation due to the great standard deviation in comparison with the mean. The usefulness of the prediction model should be confirmed in patients with high preoperative corneal astigmatism.