ABSTRACT
Over the past two decades dramatic improvements in microsurgical techniques have resulted in penetrating keratoplasty (PKP) becoming a more common and successful procedure, with over 40,000 surgeries performed annually.1 Unfortunately, refractive errors postoperatively continue to challenge the visual rehabilitation of these patients. Most patients will not tolerate more than three diopters of anisometropia, due to image size disparity or astigmatism of greater than one and a half to three to 3 diopters.2-3 Refractive unpredictability following penetrating keratoplasty is extremely common, due to the inherent imprecision of the operation with most series documenting mean cylinders of four to five diopters and significant anisometropia.4-10 The residual refractive error may be due to surgical technique, wound healing and donor tissue variables, and is often further complicated by implantation of an intraocular lens. Refractive anisometropia and high postoperative astigmatism can compromise the patient’s return to normal binocular function. Anisometropia may result in headache, photophobia, burning, tearing, diplopia, and blurred vision.2 Binder reported in a series of patients following corneal transplant and cataract extraction that only 21 out of 43 eyes achieved refractive errors within two diopters of emmetropia.11 Davis et al evaluated patients having combined cataract extraction with penetrating keratoplasty. Only 75 percent of patients fell between −4.00 and +2.00, when emmetropia was the goal.12 Flowers, et al evaluated intraocular lens power calculation in combined corneal transplant and cataract extraction and reported that only 39 percent of patients had a refractive error within two diopters of emmetropia. The range of ametropia was from −9.75 to +12.88 diopters, with 65 percent of the patients having myopic errors.5
