title: Can the prevalence of open-angle glaucoma be estimated from a retrospective clinical material? A study on the west coast of Iceland.
abstract: OBJECTIVE
  To explore the possibility of estimating the prevalence of open-angle glaucoma (OAG) on the west coast of Iceland using a clinical retrospective material, and to compare that estimate with the results from a recent prospective Icelandic study.
  
  
  METHODS
  The compulsory ophthalmological examination for the prescription of eye glasses in combination with information obtained from Statistics Iceland were used to establish the prevalence of glaucoma in Akranes and to estimate the minimum prevalence for the greater west coast area. A recent prospective study from Iceland was used as reference.
  
  
  RESULTS
  In all, 79% of 1443 Akranes inhabitants aged 50 years or more had visited the eye clinic at least once between 1996 and 2001. The prevalence of OAG was 4.8% (95% CI 3.6-6.1). The minimum prevalence for the west coast was 3.8% (95% CI 3.2-4.4). The prevalence increased with age (p < 0.001). The overall prevalence was similar to that of recently published prospective data but the prevalence of normal tension glaucoma (NTG) was lower.
  
  
  CONCLUSIONS
  The results from the two studies are similar in many respects, which indicates that retrospective data may supply meaningful information on glaucoma prevalence. Important sources of error are the selection and attendance of patients, screening methods and diagnostic criteria. If routine examination does not include fundus photography and/or perimetry, the prevalence of NTG will be underestimated.
authors.affiliation: Department of Clinical Sciences, Ophthalmology, Umeå University, Umeå, Sweden.
authors.forename: Gauti
authors.initials: G
authors.lastname: Jóhannesson
authors.forename: Gudrún J
authors.initials: GJ
authors.lastname: Gudmundsdóttir
authors.forename: Christina
authors.initials: C
authors.lastname: Lindén
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D004812:Epidemiologic Methods; D005260:Female; D005902:Glaucoma, Open-Angle / Q000453:epidemiology*; D006801:Humans; D007055:Iceland / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011446:Prospective Studies; D012042:Registries; D012189:Retrospective Studies