Effect of limbal relaxing incisions during phacoemulsification surgery based on nomogram review and numerical simulation.

PURPOSE: To determine the effect of the parameters related to limbal incisions (length, depth, optical zone, and so on) by revision of different nomograms and analyzing the outcomes of numerical simulation of incisions with a biomechanical model of the cornea.

METHODS

The Cristóbal nomogram was developed based on our experience on the performance of relaxing incisions to correct astigmatism. A numerical model of the eye was used to analyze the effect induced by variation of each parameter compiled in nomograms. The biomechanical properties remained invariable for all cases. Different incisions were simulated to study the influence of each parameter, being one varied while the others remain constant, under equal biomechanical conditions, ignoring the human factor.

RESULTS

Quantitatively, simulation of incisions of 45, 60, and 90 degrees; optical zone of 10 mm; and depth of 90% of the thickness induced astigmatic changes of 1.2, 1.4, and 1.9 diopters (D). Paired incisions at 7.5-mm optical zone and 90-degree length induced astigmatic changes of 0.7, 2.6, and 4.4 D for 40%, 75%, and 90% depth, respectively. Paired incisions of 90-degree length and 90% depth for 10- and 7.5-mm optical zones induced 1.9 and 4.4 D, respectively. Qualitatively, the results confirm the guidelines compiled in nomograms.

CONCLUSIONS

The revision of some nomograms for limbal incisions to correct astigmatism, compared with the outcomes of numerical simulation, leads to common guidelines. Numerical simulation supplies theoretical outcomes that the clinician can take into account to decide the values of the parameters for the surgery, in addition to their clinical experience.