Research Article: Graft-size selection and anisometropia reduction in penetrating keratoplasty (PKP)

Date Published: June 20, 2019

Publisher: Public Library of Science

Author(s): Ellen H. Koo, William J. Feuer, Richard K. Forster, Yan Li.


To compare the amount of myopia induced by same-size donor-to-host penetrating keratoplasty with that of the amount of myopia induced by over-sized donor-to-host penetrating keratoplasty.

Tertiary referral academic center.

Retrospective cohort study.

Charts from patients who underwent penetrating keratoplasty by the same technique at Bascom Palmer Eye Institute between Nov 1, 2002, and January 1, 2006, were reviewed. The patients underwent optical penetrating keratoplasty using 12 interrupted 10–0 nylon sutures and a 12-bite continuous 10–0 nylon suture by a single surgeon (R.K.F.). The surgical technique used would be considered standard of care at most institutions. The Institutional Review Board, University of Miami Human Subjects Research Office, approved the study protocol. The donor graft was over-sized by 0.25mm in eyes when the intended final refractive target was greater than -1.00 diopters spherical equivalent (SE). The same-size donor graft was used when the intended final refractive target was less than -1.00 diopters SE. The selection of donor graft size was entirely based upon clinical parameters, meaning that the intended final refractive target was determined per each patient’s fellow eye refraction, with the intention of reducing anisometropia. All patients received postoperative refraction and corneal topography. These measurements were performed at 6–8 weeks when the initial removal of sutures commenced, then at 6 months, then after completion of selective suture removal, then again at 12 months.

At 12 months, the over-sized group resulted in -1.35 diopters (SD = 2.25) SE of refraction, and the same-size group resulted in -0.14 diopters (SD = 2.42) SE. This approached statistical significance (p = 0.052) in comparison to -1.00 diopters spherical equivalent.

Using a donor graft that is over-sized by 0.25mm results in refraction of -1.00 diopters SE or more of myopia. Using a same-size donor-graft results in refraction of less than -1.00 diopters SE. Therefore, careful graft-size selection can result in a more favorable clinical outcome—namely, reduction in anisometropia—in patients undergoing penetrating keratoplasty.

Partial Text

One of the biggest challenges after penetrating keratoplasty (PKP) is the management of the patient’s refractive outcome. To this date, the refractive outcome after PKP still remains variable, even though graft survival rate 3–5 years following penetrating keratoplasty has reached 90%[1–3]. The lack of predictability is a challenge both for clinician and the patient, as a reasonable refractive outcome translates into meaningful vision for the patient.

Penetrating keratoplasty (PKP) continues to play an important role in visual rehabilitation for patients with corneal opacities. However, a clear cornea is usually insufficient for meaningful visual functioning for the patient. The refractive outcomes—which include myopia, astigmatism and anisometropia—need to be optimized in order to maximize visual functioning. Unwanted extremes in refractive outcomes after penetrating keratoplasty continue to be a challenge in visual rehabilitation after penetrating keratoplasty. Anisometropia needs to be minimized to allow for successful binocular visual functioning for the patient after penetrating keratoplasty.