title: Clinical characteristics influence screening intervals for diabetic retinopathy.
abstract: OBJECTIVE
  Most guidelines recommend annual screening for diabetic retinopathy (DR) but limited resources and the slow progression of DR suggest that longer recall intervals should be considered if patients have no detectable lesions. This study aimed to identify the cumulative incidence and time of development of referable DR in patients with no DR at baseline, classified by clinical characteristics.
  
  
  METHODS
  Analysis was performed of data collected prospectively over 20 years in a screening clinic based in a teaching hospital according to a consensus protocol. The cumulative incidence, time of development and relative risk of developing referable retinopathy over 6 years following a negative screening for DR were calculated in 4,320 patients, stratified according to age at onset of diabetes (<30 or ≥ 30 years), being on insulin treatment at the time of screening and known duration of diabetes (<10 or ≥ 10 years).
  
  
  RESULTS
  The 6 year cumulative incidence of referable retinopathy was 10.5% (95% CI 9.4, 11.8). Retinopathy progressed within 3 years to referable severity in 6.9% (95% CI 4.3, 11.0) of patients with age at onset ≥ 30 years, who were on insulin treatment and had a known disease duration of 10 years or longer. The other patients, especially those with age at onset <30 years, on insulin and <10 years duration, progressed more slowly.
  
  
  CONCLUSIONS
  Screening can be repeated safely at 2 year intervals in any patient without retinopathy. Longer intervals may be practicable, provided all efforts are made to ensure adherence to standards in procedures and to trace and recall non-attenders.
authors.affiliation: Diabetic Retinopathy Centre, Department of Medical Sciences, University of Turin, Corso AM Dogliotti 14, 10126 Turin, Italy. massimo.porta@unito.it
authors.forename: Massimo
authors.initials: M
authors.lastname: Porta
authors.forename: Mauro
authors.initials: M
authors.lastname: Maurino
authors.forename: Sara
authors.initials: S
authors.lastname: Severini
authors.forename: Elena
authors.initials: E
authors.lastname: Lamarmora
authors.forename: Marina
authors.initials: M
authors.lastname: Trento
authors.forename: Elena
authors.initials: E
authors.lastname: Sitia
authors.forename: Eleonora
authors.initials: E
authors.lastname: Coppo
authors.forename: Alessandro
authors.initials: A
authors.lastname: Raviolo
authors.forename: Stefania
authors.initials: S
authors.lastname: Carbonari
authors.forename: Marcello
authors.initials: M
authors.lastname: Montanaro
authors.forename: Lorenza
authors.initials: L
authors.lastname: Palanza
authors.forename: Paola
authors.initials: P
authors.lastname: Dalmasso
authors.forename: Franco
authors.initials: F
authors.lastname: Cavallo
mesh_terms: D000328:Adult; D001766:Blindness / Q000517:prevention & control; D003922:Diabetes Mellitus, Type 1 / Q000150:complications; D003924:Diabetes Mellitus, Type 2 / Q000150:complications; D003930:Diabetic Retinopathy / Q000175:diagnosis* / Q000209:etiology / Q000473:pathology; D005260:Female; D006801:Humans; D008297:Male