Radial keratotomy: III. Relationship between wound gape and corneal curvature in primate eyes

The relationship between changes in wound gape and corneal curvature after radial keratotomy (RK) was evaluated in five primates. Four-incision RK was performed using a diamond knife set to 100% of central corneal thickness with a 3-mm optical zone. In vivo measurements of wound gape were obtained using tandem scanning confocal microscopy at 3, 7, 14, and 45 days after surgery. The changes in corneal contour were measured at the same time points using a corneal modeling system with a specially designed primate cone. Wounds progressively increased in width to a maximum of 38 ± 1 μm (n = 5) at day 7. After day 7, wounds showed increasing fibrosis which correlated with decreasing wound gape to 20 ± 1 μm at day 45. A similar temporal change was detected in central corneal curvature (K), with maximum flattening occurring at day 7 (ΔK = -3.17 ± 0.90 diopters, n = 5), and progressive regression of effect to 1.32 ± 0.61 diopters (n = 5) at day 45. Although there was interanimal variation, the mean temporal changes in corneal curvature significantly paralleled the changes in wound gape (r = -0.96, n = 4, P < 0.05). Based upon these findings, a simple geometric model was proposed which provides a hypothetic foundation for the relationship between corneal curvature and wound gape after RK. Calculations of wound gape made from this analytic model (using the measured topographic data) showed significant correlation with the actual wound gape measurements (r = 0.96, n = 4, P < 0.05). These data support the hypothesis that, after RK, changes in wound gape during wound healing are directly related to refractive changes. Based on parallel studies which demonstrate the coincident appearance of wound fibrosis with the initiation of incisional wound closure, it is hypothesized that contractile elements developing within the wound directly modulate wound gape and thus determine final corneal curvature after wound healing.