title: Nonarteritic anterior ischemic optic neuropathy: refractive error and its relationship to cup/disc ratio.
abstract: OBJECTIVE
  To investigate refractive error in eyes with nonarteritic anterior ischemic optic neuropathy (NA-AION) and its relationship to cup/disc (C/D) ratio.
  
  
  METHODS
  Cohort study.
  
  
  METHODS
  A total of 608 consecutive patients with NA-AION.
  
  
  METHODS
  At first visit, all patients had a comprehensive ophthalmic evaluation, including recording best-corrected visual acuity, visual fields, anterior segment examination, ophthalmoscopy, and fluorescein fundus angiography. Morphometric measurement of C/D ratio was performed in 65 fellow normal eyes in patients with unilateral NA-AION. Refraction was converted into spherical equivalent for data analysis. The data were analyzed using Pearson correlation, Mantel-Haenszel chi-square test, Cochran-Mantel-Haenszel test, chi-square goodness-of-fit test, and segmented linear regression.
  
  
  METHODS
  Refractive error in NA-AION eyes and any association between refractive error and C/D ratio.
  
  
  RESULTS
  Mean age of patients with NA-AION was 60.9 (standard deviation [SD] = 12.6; range 20.5-95.2) years. Median time from onset to refraction was 2 weeks (interquartile range 1-5 weeks). There was a significant association between spherical equivalent and age (P<0.0001). Comparison of refraction in patients with NA-AION who were aged >or=50 years with that of an age-matched general population in the Framingham study cohort showed no significant difference between the 2 groups (P = 0.289). Comparison with the age-matched US population from the 1999-2000 National Health and Nutrition Examination Survey showed a higher proportion of NA-AION eyes with spherical equivalent from -0.5 to 0.5 diopters and a smaller proportion with -3 to <-0.5 and >0.5 to +3 diopters (P<0.001). For horizontal C/D ratio, a higher degree of myopia and higher degree of hyperopia were significantly associated with a larger C/D ratio (P<0.021). A similar pattern was seen for vertical C/D ratio in hyperopia (P = 0.057) but not in myopia (P = 0.428).
  
  
  CONCLUSIONS
  There was a significant association between spherical equivalent refraction and age (P<0.0001). C/D ratio in persons with NA-AION is significantly smaller than that seen in the general population. Morphometric study in patients with NA-AION showed that a higher degree of myopia and higher degree of hyperopia are significantly associated with a larger C/D ratio.
  
  
  BACKGROUND
  The authors have no proprietary or commercial interest in any materials discussed in this article.
authors.affiliation: Department of Ophthalmology and Visual Sciences, College of Medicine, University of Iowa, Iowa City, Iowa, USA. sohan-hayreh@uiowa.edu
authors.forename: Sohan Singh
authors.initials: SS
authors.lastname: Hayreh
authors.forename: M Bridget
authors.initials: MB
authors.lastname: Zimmerman
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001167:Arteritis / Q000503:physiopathology; D015331:Cohort Studies; D005260:Female; D005451:Fluorescein Angiography; D006801:Humans; D008297:Male; D008875:Middle Aged; D009898:Optic Disk / Q000473:pathology*; D018917:Optic Neuropathy, Ischemic / Q000175:diagnosis / Q000503:physiopathology*; D011446:Prospective Studies; D012030:Refractive Errors / Q000175:diagnosis / Q000503:physiopathology*; D014792:Visual Acuity / Q000502:physiology