Corneal shape changes after pars plana vitrectomy.

Abstract

The purpose of this prospective, controlled, clinical study was to investigate corneal shape changes due to pars plana vitrectomy (PPV) in patients with potential visual improvement postoperatively. A total of 36 consecutive patients undergoing conventional PPV combined with or without macular surgery were studied. Sequential determinations of the corneal curvature by manual keratometry and corneal topography were performed preoperatively, during the first postoperative week, at 4 weeks and after 2-8 months (mean 4 months). The mean surgically induced keratometric astigmatism was 2.92 +/- 1.98 diopters (D) (P < 0.0001) during the first postoperative week. After 4 weeks and 4 months the values decreased to 1.01 +/- 0.97 D and 0.67 +/- 0.43 D, respectively. Videokeratographic analysis confirmed significant curvature changes, with corneal steepening (P < 0.008) which corresponded to the superonasal and temporal semimeridian, and flattening (P < 0.008) along the inferior and inferonasal semimeridians. Corneal changes persisted in some cases for several weeks, partly in an asymmetric and irregular configuration. Shifts in axis to against-the-rule and oblique meridians were noted postoperatively with redistribution within preoperative values in 53% of the cases at 4 weeks after surgery. Subgroup analysis revealed that suture diameter, as well as the use of gas endotamponade, influenced the induced astigmatism. A substantial increase of the corneal astigmatism and distinct shape changes can occur after PPV in the immediate postoperative period. Consecutive stabilization at preoperative values was observed after several weeks. The time course of the corneal curvature alterations should be considered in the postoperative management to detect refractive causes of inadequate visual acuity.