title: Relationship between patient age and refractive index of the corneal stroma during refractive surgery assisted by femtosecond laser flap creation.
abstract: OBJECTIVE
  To measure the refractive index (RI) of the human corneal stroma in vivo using an objective Abbé refractometer (VCH-1) and to determine if RI of the stroma is related to age.
  
  
  METHODS
  VCH-1 was used to measure RI at the central anterior stroma immediately after lifting the flap in neophyte patients preselected for laser in situ keratomileusis. Surgical procedures continued as preplanned after measuring the RI, and in binocular cases, measurements were taken from the right eye only. Corneal flaps were created using a femtosecond laser system.
  
  
  RESULTS
  Mean RI (±SD, range) and age (±SD, range) values were 1.373 (±0.006, 1.358-1.385) and 36.55 (±12.26, 18-74). A significant linear correlation was found between age and RI. Least squares regression lines equating RI with age (x, years) were of the form: RI = 1.36911 + 0.000096x (r = +0.195; n = 115; P = 0.037). Mean RI (± SD) in the 2 age groups separated by the median age (≤34 and ≥35) were 1.371 (±0.007; n = 57) and 1.374 (±0.005; n = 58). The difference was statistically significant (P = 0.018).
  
  
  CONCLUSIONS
  RI of the anterior stroma in vivo tends to be increased in older patients when the corneal flap is created using a femtosecond laser device.
authors.affiliation: Research, Development and Innovation Department, VISSUM, Instituto Oftalmologico de Alicante, Alicante, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Amparo
authors.forename: Sudi
authors.initials: S
authors.lastname: Patel
authors.forename: Jorge L
authors.initials: JL
authors.lastname: Alió
authors.forename: Jose L
authors.initials: JL
authors.lastname: Rodriguez-Prats
authors.forename: Luis J
authors.initials: LJ
authors.lastname: Moreno
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D003319:Corneal Stroma / Q000502:physiology*; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology*; D013524:Surgical Flaps; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult