Corneal Allograft Intrastromal Ring Segment Implantation In Keratoconus - Tomographic Findings And Visual Acuity

To evaluate the effect of corneal allograft intrastromal ring segments on the corneal elevation and to correlate those changes with visual acuity outcomes.

Retrospective, nonrandomized, interventional case series. Ring segment-shaped corneal allografts (KeraNatural^TM) were implanted in intrastromal tunnels created using a femtosecond laser in 65 keratoconic eyes of 49 consecutive patients. Computed tomography scans of the corneal surfaces ​​were performed with the Scheimpflug image camera preoperatively and postoperatively and  repeated measures ANOVA test was used to compare the parameters. Pearson’s correlation coefficient was used to measure the strength of the correlation between corneal elevation changes and changes in visual acuity.

Mean age was 29.5 ± 7.3 years (median 29, range: 20 to 52 years). Mean postoperative follow-up time was 14.3 ± 4.0 months (median: 14, range: 6 to 23 months). Anterior corneal surfaces showed statistically significant decreases in average flat kera­tometry (K1), steep kera­tometry (K2), and maximum kera­tometry (Kmax) after surgery (p<0.01 for all). The anterior and posterior best-fit spheres were flattened significantly (p<0.01).  Mean anterior and posterior maximum elevation were also decreased significantly (p<0.01).  A moderate correlation was found between the change in posterior maximum elevation and uncorrected distance visual acuity (r=-0.408, p=0.048), and corrected distance visual acuity (r= -0.481, p=0.017), respectively. 

This study demonstrated that implantation of KeraNatural ring segments changes corneal tomographic parameters in both anterior and posterior surfaces with an ensuing corneal regularization. Despite the changes in both corneal surfaces, there was a moderate correlation merely between posterior maximum elevation and vision improvement.