title: Seasonality and incidence of central retinal vein occlusion in Sweden: a 6-year study.
abstract: OBJECTIVE
  To investigate seasonality in onset and incidence of central retinal vein occlusion (CRVO) in Stockholm, Sweden.
  
  
  METHODS
  A retrospective consecutive population-based case series of patients presenting to the emergency department with CRVO from January 2008 through December 2013 at the St Erik Eye Hospital. Date, age at occurrence and sex were recorded in the study cohort.
  
  
  RESULTS
  A total of 854 patients presented with CRVO during the study period. Peak CRVO onset occurred during the winter/spring period and was significantly higher than during the summer/autumn period. The number of patients presenting by season were: 166 (28.8%, 95% confidence interval, CI, 25.3-32.6%) in winter, 172 (29.9%, 95% CI 26.3-33.7%) in spring, 131 (22.7%, 95% CI 19.5-26.3%) in summer, and 107 (18.9%, 95% CI 15.6-22.0%) in autumn (p < 0.0002). There were more males, accounting for 53.9% of subjects (460/856; p = 0.029). Mean annual incidence of CRVO was 2/10,000 for persons aged over 40 years, increasing from 0.25/10,000 at 45 years to 7/10,000 at 85 years (p < 0.001).
  
  
  CONCLUSIONS
  The onset of CRVO in Stockholm, Sweden, had a significant seasonal pattern and most cases occurred during the winter-spring period. The highest incidence of CRVO was found in elderly people.
authors.affiliation: Karolinska Institutet, St Eriks Eye Hospital , Stockholm , Sweden , and.
authors.forename: David
authors.initials: D
authors.lastname: Epstein
authors.forename: Anders
authors.initials: A
authors.lastname: Kvanta
authors.forename: Pelle G
authors.initials: PG
authors.lastname: Lindqvist
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D012170:Retinal Vein Occlusion / Q000453:epidemiology*; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons; D013548:Sweden / Q000453:epidemiology
keywords: Central retinal vein occlusion; Sweden; incidence; seasonality; vitamin D