title: Intrastromal Corneal Ring Segment Implantation in 409 Paracentral Keratoconic Eyes.
abstract: OBJECTIVE
  To assess the efficacy outcomes of implanting intrastromal corneal ring segments (ICRS) to correct paracentral keratoconus.
  
  
  METHODS
  Four hundred nine eyes with paracentral keratoconus, in which the differences between the axes of refractive cylinder and the corneal flattest meridian and the comatic aberration map were less than 30 degrees, were evaluated before and after the implantation of Ferrara-type ICRS. Snellen uncorrected and best-corrected distance visual acuity, residual refractive errors analyzed with vector analysis, and the root mean square for corneal coma-like aberration for a pupil size of 4.5 mm were recorded before and 6 months after ICRS implantation.
  
  
  RESULTS
  The mean uncorrected distance visual acuity (Snellen decimal scale) rose from 0.19 ± 0.19 before ICRS implantation to 0.42 ± 0.30 after implantation (P < 0.0001). The mean preoperative best-corrected distance visual acuity was 0.69 ± 0.24 and the postoperative value was 0.77 ± 0.23 (P < 0.0001). The safety index was 1.13. The spherical equivalent declined steeply after ICRS implantation (P < 0.0001). Cylinder power decreased by more than 50% in 71% of the eyes. The root mean square for corneal coma-like aberration for a 4.5-mm pupil changed from 1.32 ± 1.01 μm before surgery to 1.06 ± 0.85 μm after surgery (P ≤ 0.001).
  
  
  CONCLUSIONS
  The Ferrara-type ICRS implantation is a safe and effective procedure for treating patients with keratoconus that meets the morphological characteristics of the sample under study.
authors.affiliation: *Fernández-Vega Ophthalmological Institute, Oviedo, Madrid, Spain; †Optics II Department, Optics and Optometry Faculty, Complutense University of Madrid, Spain; and ‡Surgery Department, School of Medicine, University of Oviedo, Oviedo, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Fernández-Vega Cueto
authors.forename: Carlos
authors.initials: C
authors.lastname: Lisa
authors.forename: Aranzazu
authors.initials: A
authors.lastname: Poo-López
authors.forename: David
authors.initials: D
authors.lastname: Madrid-Costa
authors.forename: Jesús
authors.initials: J
authors.lastname: Merayo-Lloves
authors.forename: Jose F
authors.initials: JF
authors.lastname: Alfonso
mesh_terms: D000328:Adult; D063171:Corneal Pachymetry; D003319:Corneal Stroma / Q000601:surgery*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019736:Prostheses and Implants; D019919:Prosthesis Implantation; D012029:Refraction, Ocular / Q000502:physiology; D012030:Refractive Errors / Q000503:physiopathology; D041623:Tomography, Optical Coherence; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult