Effect of incision location on preoperative oblique astigmatism after scleral tunnel incision.

Purpose: To evaluate the effect of incision location or clinically relevant preoperative oblique astigmatism.

Setting: Department of Ophthalmology, Virchow Medical Center, Humboldt-University, Berlin, Germany.

Methods: This prospective study included 68 patients who had phacoemulsification and posterior chamber lens implantation using a standardized 7.0 mm self-sealing trapezoidal scleral tunnel incision. Each patient was randomly assigned to one of three incision locations: Group A, conventional superior incision; Group B, temporal incision; Group C, oblique incision centered on the steeper meridian (modified BENT incision). Astigmatism analysis was performed by manual keratometry and corneal topography.

Results: A significant mean reduction in astigmatism of 0.58 diopter (D) (P < .01) was achieved in only the modified BENT incision group. Postoperatively, significant flattening of 0.27 D (P < .01) in the steeper meridian as well as steepening of 0.29 D (P < .01) in the flatter meridian occurred. No decrease in astigmatism was noted in the superior or temporal incision groups. Five months postoperatively, vector analysis showed that surgically induced astigmatism was significantly higher in the superior incision group (1.16 D +/- 0.44 [SD]) than in the temporal incision group (0.66 +/- 0.32 D) or modified BENT incision group (0.82 +/- 0.50 D). Corneal topographic analysis confirmed these results within +/- 0.3 D.

Conclusions: Only the oblique incision centered on the steeper meridian (modified BENT incision) effectively and predictably reduced preoperative oblique astigmatism. In eyes with clinically relevant oblique astigmatism, we recommend using a modified BENT incision.