title: Keratometric index obtained by Fourier-domain optical coherence tomography.
abstract: OBJECTIVE
  To determine the keratometric indices calculated based on parameters obtained by Fourier-domain optical coherence tomography (FD-OCT).
  
  
  METHODS
  The ratio of anterior corneal curvature to posterior corneal curvature (Ratio) and keratometric index (N) were calculated within central 3 mm zone with the RTVue FD-OCT (RTVue, Optovue, Inc.) in 186 untreated eyes, 60 post-LASIK/PRK eyes, and 39 keratoconus eyes. The total corneal powers were calculated using different keratometric indices: Kcal based on the mean calculated keratometric index, K1.3315 calculated by the keratometric index of 1.3315, and K1.3375 calculated by the keratometric index of 1.3375. In addition, the total corneal powers based on Gaussian optics formula (Kactual) were calculated.
  
  
  RESULTS
  The means for Ratio in untreated controls, post-LASIK/PRK group and keratoconus group were 1.176 ± 0.022 (95% confidence interval (CI), 1.172-1.179), 1.314 ± 0.042 (95%CI, 1.303-1.325) and 1.229 ± 0.118 (95%CI, 1.191-1.267), respectively. And the mean calculated keratometric index in untreated controls, post-LASIK/PRK group and keratoconus group were 1.3299 ± 0.00085 (95%CI, 1.3272-1.3308), 1.3242 ± 0.00171 (95%CI, 1.3238-1.3246) and 1.3277 ± 0.0046 (95%CI, 1.3263-1.3292), respectively. All the parameters were normally distributed. The differences between Kcal and Kactual, K1.3315 and Kactual, and K1.3375 and Kactual were 0.00 ± 0.11 D, 0.21 ± 0.11 D and 0.99 ± 0.12 D, respectively, in untreated controls; -0.01 ± 0.20 D, 0.85 ± 0.18 D and 1.56 ± 0.16 D, respectively, in post-LASIK/PRK group; and 0.03 ± 0.67 D, 0.56 ± 0.70 D and 1.40 ± 0.76 D, respectively, in keratoconus group.
  
  
  CONCLUSIONS
  The calculated keratometric index is negatively related to the ratio of anterior corneal curvature to posterior corneal curvature in untreated, post-LASIK/PRK, and keratoconus eyes, respectively. Using the calculated keratometric index may improve the prediction accuracies of total corneal powers in untreated controls, but not in post-LASIK/PRK and keratoconus eyes.
authors.affiliation: Department of Ophthalmology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, 200233, China.
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Hua
authors.affiliation: Department of Ophthalmology, University Hospital of North Norway, Tromsø, Norway; SynsLaser Kirurgi AS, Tromsø/Oslo, Norway.
authors.forename: Aleksander
authors.initials: A
authors.lastname: Stojanovic
authors.affiliation: Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Tor Paaske
authors.initials: TP
authors.lastname: Utheim
authors.affiliation: SynsLaser Kirurgi AS, Tromsø/Oslo, Norway.
authors.forename: Xiangjun
authors.initials: X
authors.lastname: Chen
authors.affiliation: SynsLaser Kirurgi AS, Tromsø/Oslo, Norway.
authors.forename: Sten
authors.initials: S
authors.lastname: Ræder
authors.affiliation: School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Key Laboratory of Vision Science, Ministry of Health of People's Republic of China, Wenzhou, Zhejiang, People's Republic of China.
authors.forename: Jinhai
authors.initials: J
authors.lastname: Huang
authors.affiliation: School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Key Laboratory of Vision Science, Ministry of Health of People's Republic of China, Wenzhou, Zhejiang, People's Republic of China.
authors.forename: Qinmei
authors.initials: Q
authors.lastname: Wang
mesh_terms: D000328:Adult; D003315:Cornea / Q000503:physiopathology / Q000601:surgery*; D005583:Fourier Analysis; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology / Q000601:surgery*; D020731:Keratomileusis, Laser In Situ; D008875:Middle Aged; D018903:Photorefractive Keratectomy; D012029:Refraction, Ocular / Q000502:physiology*; D041623:Tomography, Optical Coherence; D055815:Young Adult