Subbasal nerve regeneration after penetrating keratoplasty

To evaluate subbasal nerve regeneration, corneal sensitivity, and tear film function after penetrating keratoplasty.

Twenty keratoplasty patients were assessed before and 1, 3, 6, and 12 months after penetrating keratoplasty by using noncontact corneal esthesiometry, tear breakup time measurement, the phenol red thread test, and confocal microscopy. Ten healthy control subjects were also assessed by using these techniques on 1 occasion. Subbasal nerve images were analyzed by using customized software to evaluate nerve regeneration.

Before surgery, the subbasal nerve plexus could be imaged only in 11 patients because of the existence of pathology. Significant deficits in nerve morphology were apparent in these patients compared with control subjects. No subbasal nerves were detected over the 12-month postoperative period. Central corneal sensitivity decreased significantly after surgery and returned to near normal levels after 12 months. Tear breakup time was significantly shorter at 3 and 12 months after keratoplasty. There were no significant differences in the phenol red thread test results before and after surgery.

There is no direct association between subbasal nerve fiber regeneration, central corneal sensitivity, and tear film stability and volume. The apparent recovery of corneal sensitivity to normal levels 12 months postoperatively, in the absence of clinically observable subbasal nerves, may be a methodologic phenomenon related to the inability of current-generation confocal microscopes to image fine regenerating nerves that mediate corneal sensibility.