Intrastromal Corneal Ring Segments: Effect of Depth of Implantation in Visual, Refractive and Topographic Outcomes in Keratoconus Patients.

Abstract

To evaluate visual, refractive and topographic outcomes of intracorneal ring segment implantation in relation to the achieved segment depth, using the manual technique. Ophthalmology Department, Hospital de Braga, Braga, Portugal. Retrospective cohort study. We obtained 104 eyes of 93 keratoconus patients submitted to Ferrara intracorneal ring segment (ICRS) implantation, using a manual technique. Subjects were divided into 3 groups according to the achieved depth of implantation: 40-70% (Group 1), 70-80% (Group 2), and 80-100% (Group 3). Visual, refractive and topographic variables were evaluated at baseline and 6-months. Topographic measurement was performed using Pentacam. Thibos-Horner and Alpins methods were used to analyze the vectorial change of refractive and topographic astigmatism, respectively. We found a significant improvement of UDVA and CDVA in all groups at 6-months (P<0.005); no differences were observed regarding safety and efficacy indexes in the three groups (p>0.05). Manifest cylinder and spherical equivalent significantly reduced in all groups (P<0.05). Topographic evaluation showed a significant improvement of all parameters in the three groups (P<0.05). A shallower (group 1) or deeper (group 3) implantation was associated with topographic cylinder overcorrection, a higher magnitude of error and a higher mean centroid postoperative corneal astigmatism. ICRS implantation with manual technique showed to be equally effective in terms of visual and refractive outcomes despite the depth of implantation; however, shallower or deeper implants were associated with topographic overcorrection and a higher mean centroid postoperative astigmatism, which explain the lower topographic predictability associated with manual surgery for ICRS implantation.