title: Unilateral keratoconus. Incidence and quantitative topographic analysis.
abstract: OBJECTIVE
  This study was designed to determine the incidence of unilaterality in a population of patients with clinical keratoconus and to compare quantitative descriptors of topography between affected corneas from patients with unilateral keratoconus and corneas of patients with bilateral disease.
  
  
  METHODS
  Retrospective clinical study with new evaluation of some patients.
  
  
  METHODS
  One hundred sixty-four patients from the University of Texas South-western Medical Center and Wills Eye Hospital who were diagnosed to have moderate-to-advanced keratoconus on the basis of characteristic topographic patterns associated with corneal thinning.
  
  
  METHODS
  Corneal topography was evaluated in both eyes of each patient.
  
  
  METHODS
  Quantitative descriptors of corneal topography were compared between 5 affected corneas of patients with unilateral keratoconus (combined cases from University of Texas Southwestern, LSU Eye Center, and Wills Eye Hospital) and 15 corneas of patients with moderate-to-advanced bilateral keratoconus (1 cornea from each patient). Indices selected for statistical analysis were the Keratoconus Predication Index (KPI), Surface Asymmetry Index (SAI), and Surface Regularity Index (SRI).
  
  
  RESULTS
  Three (1.83%) of 164 patients with moderate-to-advanced keratoconus had no topographic evidence of keratoconus in the opposite eye. There were no statistically significant differences in KPI, SRI, or SAI values between the affected corneas of patients with unilateral and bilateral keratoconus. Over a period of 4 years of observation, signs of keratoconus in the previously normal eye developed in a patient with unilateral keratoconus.
  
  
  CONCLUSIONS
  The authors found no differences in the quantitative descriptors of corneal topography between corneas with keratoconus from unilateral and bilateral cases. The authors' results suggest that the incidence of "unilateral" keratoconus is very low. Patients initially diagnosed with unilateral keratoconus, if observed for a sufficient period, commonly had signs of keratoconus develop in the opposite eye. The possibility that all cases of unilateral keratoconus may eventually become bilateral cannot be excluded. Therefore, refractive surgical procedures should not be performed on apparently normal corneas when keratoconus is detected in the opposite eye.
authors.affiliation: Department of Ophthalmology, University of Texas Southwestern Medical Center at Dallas, USA.
authors.forename: D R
authors.initials: DR
authors.lastname: Holland
authors.forename: N
authors.initials: N
authors.lastname: Maeda
authors.forename: S B
authors.initials: SB
authors.lastname: Hannush
authors.forename: L H
authors.initials: LH
authors.lastname: Riveroll
authors.forename: M T
authors.initials: MT
authors.lastname: Green
authors.forename: S D
authors.initials: SD
authors.lastname: Klyce
authors.forename: S E
authors.initials: SE
authors.lastname: Wilson
mesh_terms: D003315:Cornea / Q000473:pathology*; D007839:Functional Laterality; D006801:Humans; D007091:Image Processing, Computer-Assisted; D015994:Incidence; D007640:Keratoconus / Q000453:epidemiology* / Q000473:pathology; D010414:Pennsylvania / Q000453:epidemiology; D012189:Retrospective Studies; D013781:Texas / Q000453:epidemiology