title: Internal, corneal, and refractive astigmatism as prognostic factors for intrastromal corneal ring segment implantation in mild to moderate keratoconus.
abstract: OBJECTIVE
  To improve the predictability of the visual and refractive outcomes of intrastromal corneal ring segment (ICRS) implantation in keratoconus patients and highlight the importance of internal astigmatism and its relationship to corneal and refractive astigmatism as prognostic factors.
  
  
  METHODS
  Vissum Corporación, Alicante, and Centro de Oftalmología Barrquer, Barcelona, Spain.
  
  
  METHODS
  Retrospective case series.
  
  
  METHODS
  Visual, refractive, topographic, and aberrometric variables were evaluated in eyes having ICRS implantation. The eyes were divided into 2 groups according to the relative position of the keratometric axis and refractive axis; that is, coincident axis (0 degree ± 15 [SD]) or uncoincident axis. Internal astigmatism was calculated by vectorial analysis. The relationship between topographic astigmatism and refractive astigmatism was evaluated. The follow-up was 6 months.
  
  
  RESULTS
  Of the 127 eyes evaluated, 79 had grade II keratoconus and 48 had grade I keratoconus. Statistically significant differences were found in the relative position of the refractive axis and keratometric axis (P=.017). Internal astigmatism had a significant correlation with the gain in visual acuity in patients with grade II keratoconus (r = -0.455, P=.0001). This relationship was less significant in patients with grade I keratoconus (r = -0.391, P=.021).
  
  
  CONCLUSIONS
  The predictability of visual and refractive outcomes can be significantly increased in grade II keratoconus patients when the relative position of the keratometric and refractive axes; the internal, corneal, and refractive astigmatism; and their combinations are used as prognostic factors.
  
  
  BACKGROUND
  No author has a financial or proprietary interest in any material or method mentioned.
authors.affiliation: From the Division of Ophthalmology (Peña-García, Alió), Universidad Miguel Hernández, and the Keratoconus Unit (Alió, Vega-Estrada), Vissum Instituto Oftalmologico de Alicante, Alicante, and Centro de Oftalmología Barraquer (Barraquer), Barcelona, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Peña-García
authors.affiliation: From the Division of Ophthalmology (Peña-García, Alió), Universidad Miguel Hernández, and the Keratoconus Unit (Alió, Vega-Estrada), Vissum Instituto Oftalmologico de Alicante, Alicante, and Centro de Oftalmología Barraquer (Barraquer), Barcelona, Spain. Electronic address: jlalio@vissum.com.
authors.forename: Jorge L
authors.initials: JL
authors.lastname: Alió
authors.affiliation: From the Division of Ophthalmology (Peña-García, Alió), Universidad Miguel Hernández, and the Keratoconus Unit (Alió, Vega-Estrada), Vissum Instituto Oftalmologico de Alicante, Alicante, and Centro de Oftalmología Barraquer (Barraquer), Barcelona, Spain.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Vega-Estrada
authors.affiliation: From the Division of Ophthalmology (Peña-García, Alió), Universidad Miguel Hernández, and the Keratoconus Unit (Alió, Vega-Estrada), Vissum Instituto Oftalmologico de Alicante, Alicante, and Centro de Oftalmología Barraquer (Barraquer), Barcelona, Spain.
authors.forename: Rafael I
authors.initials: RI
authors.lastname: Barraquer
mesh_terms: D057128:Aberrometry; D000293:Adolescent; D000328:Adult; D001251:Astigmatism / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D003319:Corneal Stroma / Q000601:surgery*; D019781:Corneal Topography; D057108:Corneal Wavefront Aberration / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D019736:Prostheses and Implants; D019919:Prosthesis Implantation; D012029:Refraction, Ocular / Q000502:physiology*; D012189:Retrospective Studies; D014792:Visual Acuity / Q000502:physiology*; D055815:Young Adult