Intrastromal Corneal Ring Segment Surgery In Moderate And Severe Cases Of Keratoconus.

To evaluate the results of treating advanced cases of keratoconus with intrastromal corneal ring segment surgery. When the patients do not tolerate rigid contact lenses nor scleral lenses, the only possibility is corneal transplantation. However, besides this surgery’s complications and irreversibility, the current median waiting time for corneal transplantation in our practice is 12 months. Therefore, the use of intrastromal segments in advanced cases of keratoconus is not only a valuable alternative, considering its benefits, reversibility and less complications, but also its availability and access in our public health care system.

Department of Ophthalmology, Hospital de Clínicas de Porto Alegre, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil

We studied 27 cases of intrastromal corneal ring segment surgery in keratoconus patients with a maximum keratometry of at least 50 diopters. A comprehensive preoperative evaluation including visual acuity, cycloplegic refraction, corneal biomicroscopy and Scheimpflug tomography was performed. All surgeries were planned using Ferrara's nomogram. The surgical technique was composed of a manual 5 to 6 mm tunnel assisted by a calibrated diamond knife. Minimum tunnel pachymetry based on the pachymetry map should be at least 300 microns. Patients included had at least 3 months of postoperative follow up. Statistics were calculated by R-software. All surgeries were performed by the same surgeon.

Surgery was performed in 27 eyes (21 patients). 50% were males, 50% were right eyes, median age of 32, preoperative spectacles BCVA of  0.5 in 8; 0.5-0.33 in 10; and < 0.33 in 9 patients. The mean preoperative keratometry was 52.4dp (50,5 – 54,3) against 48.2dp (46,3 – 50,1) after 3 months (p < 0.05 – Paired Student-t test). Maximum keratometry was reduced from 59.5dp (57.6 – 61.3) to 52.9dp (50.8 - 54.9)(p < 0.05). Median cylinder in refraction dropped from -4.5dp to -2.5dp (p<0.05).  Postoperative spectacles BCVA of 1.0 was achieved by 3 patients and > 0.50 by 19 (against 8 pre-surgery). Two eyes had to have a segment removal after 6 months and 1 year postoperatively for superficialization, but no other complications occurred.

Results demonstrate that intrastromal corneal ring segment surgery is a feasible solution in treating moderate and severe cases of keratoconus, enabling the use of glasses with more comfortable prescriptions or even soft contact lenses. It can avoid the need for corneal transplantation in many cases, since the ring might stabilize the disease progression and provide useful vision. The most recent counter-indication is not the minimum pachymetry of the entire cornea nor its maximum keratometry, but pachymetry of the tunnel. It benefits many more patients with advanced disease, and the position between 5 and 6mm, as used in Brazil, is more powerful in reducing high curvatures than between 6 and 7mm.