Optimal size and location for corneal rotational autografts - A simplified mathematical model

Objective: To calculate clinical guidelines for the optimal location and size of a rotational autokeratoplasty. Methods: The ideal graft size and trephine decentration for a rotational autograft were calculated based on scar location using geometric models. Mathematical variables were set to maximize postoperative visual acuity and for generalization of the geometric model. This model was used in a rotational autokeratoplasty of a patient with a history of a corneal scar and diplopia. An 8-mm autograft was decentered 0.5mm superiorly and rotated 180 to relocate the scar to the superior aspect of the cornea, out of the patient's vision. Results: For cases that satisfy the given variables, a graft diameter of 8-mm with a decentration of 0.5 mm balances maximization of scar removal and scar movement superiorly, with minimization of discrepancy in corneal thickness after rotation. For scars that are alpha degrees from horizontal, the graft should be rotated 180-alpha degrees. By using these calculations, the autograft in this case successfully resolved the diplopia and improved visual acuity. Conclusions: A rotational autograft can be an effective alternative to standard penetrating keratoplasty for some patients with corneal scars. We establish a mathematical model for most clinical instances of a rotational autograft, in which an 8-mm graft with a decentration of 0.5 mm best satisfies the goals of surgery.