Reducing surgically induced astigmatism by using a scleral tunnel.

We conducted a prospective study of 36 eyes undergoing pars plana lensectomy, vitrectomy, and implantation of an intraocular lens. We used a scleral tunnel begun 3 mm posterior to the corneoscleral limbus and entered the anterior chamber through clear cornea. We found that this technique produced minimal postoperative astigmatism. After follow-up periods ranging from three to 15 months, the average change in the flatter meridian was -0.07 diopter and that in the steeper meridian was +0.26 diopter. The mean induced astigmatism was -0.33 diopter. A group of nine eyes undergoing pars plana lensectomy and vitrectomy alone showed no significant changes in the postoperative astigmatism. Statistical comparisons established that there was no significant difference between eyes undergoing intraocular lens implantation in addition to pars plana lensectomy and vitrectomy and those not undergoing intraocular lens implantation.