title: Modification and refinement of astigmatism in keratoconic eyes with intrastromal corneal ring segments.
abstract: OBJECTIVE
  To analyze corneal astigmatic changes after implantation of intrastromal corneal ring segments (ICRS) in keratoconic eyes using the Alpins vectorial method.
  
  
  METHODS
  Vissum Corporation, Alicante, Spain.
  
  
  METHODS
  Keraring ICRS were implanted in eyes with a diagnosis of keratoconus. One of 3 surgeons performed the ICRS implantations using femtosecond technology and following the same protocol. Visual, refractive, keratometric, and corneal aberrometric changes were evaluated during a 12-month follow-up. Corneal astigmatic changes were also analyzed using the following Alpins vectorial components: targeted induced astigmatism (TIA), surgically induced astigmatism (SIA), difference vector, magnitude of error, flattening effect, and torque.
  
  
  RESULTS
  Postoperatively, there was significant visual improvement (P = .03), significant central flattening (P = .03), and a significant reduction in manifest astigmatism (P<.01). The magnitude of SIA vector was significantly lower than the TIA postoperatively (P>or=.02). The mean magnitude of the difference vector 3 months postoperatively was +2.96 diopters (D) +/- 1.68 (SD). The mean magnitude of error remained negative and unchanged (P>or=.10). The mean magnitude of the flattening effect was significantly lower than the TIA at all postoperative visits (P<or=.01). The mean magnitude of torque vector was 1.21 +/- 0.98 D at 3 months. Significant negative correlations were found between preoperative corneal astigmatism and the magnitude of error and difference vector at all postoperative visits.
  
  
  CONCLUSIONS
  Although ICRS implantation significantly reduced the magnitude of corneal astigmatism, there was a trend toward undercorrection and the meridian of correction was not appropriate in all cases, showing the need for nomogram adjustments.
authors.affiliation: Keratoconus Unit, Vissum Corporation, and Departamento de Optica, Farmacología y Anatomía, Universidad de Alicante, Alicanted, Spain.
authors.forename: David P
authors.initials: DP
authors.lastname: Piñero
authors.forename: Jorge L
authors.initials: JL
authors.lastname: Alió
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Teus
authors.forename: Rafael I
authors.initials: RI
authors.lastname: Barraquer
authors.forename: Ralph
authors.initials: R
authors.lastname: Michael
authors.forename: Ramón
authors.initials: R
authors.lastname: Jiménez
mesh_terms: D057128:Aberrometry; D000293:Adolescent; D000328:Adult; D000368:Aged; D001251:Astigmatism / Q000503:physiopathology / Q000601:surgery*; D003319:Corneal Stroma / Q000601:surgery*; D019781:Corneal Topography; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D013508:Ophthalmologic Surgical Procedures; D019904:Polymethyl Methacrylate; D019736:Prostheses and Implants; D019919:Prosthesis Implantation / Q000379:methods*; D012029:Refraction, Ocular / Q000502:physiology; D012189:Retrospective Studies; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult
chemical_list: D019904:Polymethyl Methacrylate