Corneal Bniomechanical Response To Long Arc-Length Intrastromal Corneal Ring Segments Implantation In Keratoconus: 3 Year Follow-Up

Intrastromal corneal ring segments (ICRS) have been shown to be safe and effective for inducing corneal regularisation in patients with keratoconus. However, given the pathogenesis of keratoconus, it is expected that if the ICRS implantation does not provide additional support to the corneal structure, the disease will continue its natural progression after surgery, diminishing the long-term effectiveness of ICRS. Thus, given the potential time-course corneal weakness induced by the disease, longitudinal studies are needed to evaluate whether ICRS provides additional support to the corneal structure. This is the first study that longitudinally assesses the biomechanical corneal response to ICRS implantation over a 3-year follow-up.

Fernandez-Vega University Institute

Twenty-nine eyes with central keratoconus that underwent a 300° arc-length ICRS implantation were enrolled. The clinical measurements included uncorrected (UDVA) and corrected distance (CDVA) visual acuities and corneal tomographic analysis. The dynamic corneal response (DCR) parameters of the Corvis ST analyzed were: The peak distance, the Deformation amplitude ratio (DA ratio), the inverse integrated radius (IIR), the Deflection amplitude (DefA), the stiffness parameter at first applanation (SP-A1), and stress–strain index (SSI). All parameters were studied preoperatively and at 1 and 3 years postoperatively.

The mean UDVA improved from 0.79±0.36 (LogMAR) preoperatively to 0.40±0.22 postoperatively (P<0.0001). The mean CDVA changed from 0.20±0.12 (LogMAR) to 0.11±0.07 (P<0.0001). UDVA and CDVA remained stable over follow-up (P>0.06). The mean K-flat reading dipped from 46.79±2.55D preoperatively to 43.00±1.89D and 43.24±1.71D at 1- and 3-year postoperatively, respectively (P<0.0001). The mean K-steep reading declined from a pre-implant 53.21±3.49D to 46.74±2.37D and 46.92±2.19D 1- and 3-year post-implant, respectively (P<0.0001). All analysed DCR parameters showed a statistically significant change after ICRS implantation compared with preoperatively and remained unchanged between 1 and 3 years postoperatively.

The 300º arc-length ICRS implantation induced a substantial corneal flattening and visual acuity improvement over a 3-year period. The ICRS induced a stiffer corneal response that persisted over the 3-year follow-up, likely due to an enhanced biomechanical environment as evidenced by sustained changes in DCR parameter.