title: Quantitative OCT-based longitudinal evaluation of intracorneal ring segment implantation in keratoconus.
abstract: OBJECTIVE
  To characterize the geometrical properties of keratoconic corneas upon intracorneal ring segments (ICRS) implantation, using custom-developed optical coherence tomography (OCT).
  
  
  METHODS
  Ten keratoconic corneas were measured pre- and post-ICRS surgery (7, 30, and 90 days). Corneal topographic and pachymetric maps were obtained from three-dimensional (3D) images acquired with OCT, provided with custom algorithms for image analysis, distortion correction, and quantification. The 3D positioning of the ICRS was also estimated longitudinally, relative to the pupil center and iris plane.
  
  
  RESULTS
  Preoperatively, the average corneal radii of curvature were 7.02 ± 0.54 mm (anterior) and 5.40 ± 0.77 mm (posterior), and the minimum corneal thickness was 384 ± 60 μm. At 90 days, the average corneal radii of curvature were 7.26 ± 0.53 mm (anterior) and 5.44 ± 0.71 mm (posterior), and the minimum corneal thickness was 396 ± 46 μm. ICRS implantation produced a significant decrease of corneal power (by 1.71 ± 1.83 diopters [D] at 90 days). Corneal irregularities (defined by high order Zernike terms of the corneal elevation maps) and the corneal thickness distribution decreased in some patients and increased in others. The 3D ICRS depth matched the planned ICRS depth well (within 23.93 ± 23.49 μm). On average, ICRS showed an overall tilt of -6.8 ± 2.6° (temporal) and -2.1 ± 0.8° (superior) at 7 days.
  
  
  CONCLUSIONS
  Spectral OCT (sOCT) provided with distortion correction and analysis tools, is an excellent instrument for evaluating the changes produced by ICRS in keratoconic corneas, and for analyzing the 3D ICRS position during the follow up. ICRS produced flattening on the anterior corneal surface, although the benefit for corneal surface regularization varied across patients.
authors.affiliation: Instituto de Óptica Daza de Valdés, Consejo Superior de Investigaciones Científicas CSIC, 28006 Madrid, Spain. p.perez@io.cfmac.csic.es
authors.forename: Pablo
authors.initials: P
authors.lastname: Pérez-Merino
authors.forename: Sergio
authors.initials: S
authors.lastname: Ortiz
authors.forename: Nicolas
authors.initials: N
authors.lastname: Alejandre
authors.forename: Ignacio
authors.initials: I
authors.lastname: Jiménez-Alfaro
authors.forename: Susana
authors.initials: S
authors.lastname: Marcos
mesh_terms: D000328:Adult; D003319:Corneal Stroma / Q000473:pathology* / Q000601:surgery; D019781:Corneal Topography; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007640:Keratoconus / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D019736:Prostheses and Implants; D019919:Prosthesis Implantation / Q000379:methods*; D012029:Refraction, Ocular; D041623:Tomography, Optical Coherence / Q000379:methods*; D016896:Treatment Outcome; D055815:Young Adult
keywords: corneal topography; intracorneal ring segments (ICRS); keratoconus; optical coherence tomography (OCT)