Intracorneal Ring Segment Implantation for Keratoconus With Duck Phenotype
Purpose
To evaluate the efficacy and safety of implantation of Ferrara-type intrastromal corneal ring segments (ICRS) for the refractive correction of paracentral keratoconus with non coincident topographic and coma axis (Duck phenotype).
Methods
Snellen uncorrected (UDVA) and corrected (CDVA) distance visual acuity, residual refractive error, topographic parameters and aberrometry (vertical coma) were recorded before and 6 months after ICRS implantation for keratoconus. The tunnels were created with manual technique and a Ferrara intracorneal ring segment of 150º arc lenght with variable thickness was implanated on the flat axis covering the coma axis. The inclusion criteria was a difference between the topographic flat axis and the coma axis superior to 30º.
Results
The study evaluated 32 eyes of 29 patients. The mean snellen UDVA was 0.17 preoperatively and 0.39 postoperatively and the mean snellen CDVA, 0.46 and 0.59 respectively (both p<0.05). The subjective refractive cylinder improved from a mean preoperatively value of -2.99 D to -1.80 D after follow-up. 5% eyes lost lines of CDVA, two thirds of eyes gained lines of CDVA, 47% of patients gained 2 or more lines of CDVA. All topographic and aberrometry (coma for 6.00 mm pupil) parameters improved after surgery (p<0.05 for all). No intraoperative complications occurred. 2 eyes developed spontaneous ring segment extrusion because of superficial tunnel creation.
Conclusion
Intrastromal corneal ring segment implantation in eyes with paracentral keratoconus with non coincident topographic and coma axis provided good visual and refractive outcomes. A 150º segment can cover the topographic and the coma axis all together.