title: The prevalence of convergence insufficiency in Iran: a population-based study.
abstract: OBJECTIVE
  The aim was to determine the prevalence of convergence insufficiency and its relationship with age, gender and refractive error in a population-based study.
  
  
  METHODS
  In this cross-sectional study, all residents over one year old in Mashhad city, in the north east of Iran, were sampled through random stratified cluster sampling. After selecting samples and their participation in the study, they all had eye examinations including the measurement of visual acuity, refraction, binocular vision assessment, including cover test, measurement of near point of convergence and fusional vergences and finally, slitlamp biomicroscopy.
  
  
  RESULTS
  Of the 4,453 selected people, 3,132 participated in the study and finally, analyses were done with data from 2,219 individuals. The mean age of the participants was 30.5 ± 14.0 years (range: 10 to 69). The prevalence of convergence insufficiency in this study was 5.51 per cent (range: 4.51 to 6.52): 4.78 per cent (range: 3.11 to 6.45) in males and 5.86 per cent (range: 4.60 to 7.11) in females (p = 0.276). Convergence insufficiency prevalence in different age groups showed no significant linear trend; however, a significant increase was observed after the age of 60 years. The prevalence of myopia, emmetropia and hyperopia was respectively 12.1, 56.9 and 31 per cent in participants with convergence insufficiency and 15.9, 54.4 and 29.6 per cent in those without convergence insufficiency (p = 0.537). Multiple logistic regression models revealed no significant relationship between the prevalence of convergence insufficiency and age, gender or refractive errors.
  
  
  CONCLUSIONS
  This study showed that the overall prevalence of convergence insufficiency in the Iranian population was 5.46 per cent, which is lower than that in the majority of previous studies. Convergence insufficiency prevalence had no significant change with age up to the age of 60 years but increased significantly after 60 years.
authors.affiliation: Noor Research Center for Ophthalmic Epidemiology, Noor Eye Hospital, Tehran, Iran.
authors.forename: Hassan
authors.initials: H
authors.lastname: Hashemi
authors.affiliation: Department of Optometry, School of Rehabilitation, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: Payam
authors.initials: P
authors.lastname: Nabovati
authors.affiliation: Department of Medical Surgical Nursing, School of Nursing and Midwifery, Shahid Beheshti University of Medical Sciences, Tehran, Iran.|Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Khabazkhoob
authors.affiliation: Refractive Errors Research Center, School of Paramedical Sciences, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Hadi
authors.initials: H
authors.lastname: Ostadimoghaddam
authors.affiliation: Department of Optometry, School of Rehabilitation, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: Asgar
authors.initials: A
authors.lastname: Doostdar
authors.affiliation: Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Shiralivand
authors.affiliation: Department of Optometry, School of Paramedical Sciences, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Abbasali
authors.initials: A
authors.lastname: Yekta
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007492:Iran / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015835:Ocular Motility Disorders / Q000453:epidemiology*; D015995:Prevalence; D012030:Refractive Errors / Q000453:epidemiology; D017678:Sex Distribution; D066167:Slit Lamp; D055815:Young Adult
keywords: age; convergence insufficiency; gender; population-based; prevalence; refractive errors