title: Defining "occludable" angles in population surveys: drainage angle width, peripheral anterior synechiae, and glaucomatous optic neuropathy in east Asian people.
abstract: BACKGROUND
  /aim: A current consensus in epidemiological studies of primary angle closure (PAC) is to diagnose the condition only if the posterior (usually pigmented) trabecular meshwork is seen for less than 90 degrees of the angle circumference, termed an "occludable angle." The authors sought to assess the validity of this epidemiological classification by exploring the relation between drainage angle width, peripheral anterior synechiae (PAS) and glaucomatous optic neuropathy (GON).
  
  
  METHODS
  918 Mongolians and 995 Chinese Singaporeans, both groups aged 40 years and older were examined in two population based surveys. Gonioscopic angle width was graded in five categories (0 = closed to 4 = wide open) according the scheme described by Shaffer. Cases with secondary PAS were excluded.
  
  
  RESULTS
  The rate of PAS was between 0.3% and 1.7% in people with wide angles (grades 3 and 4). In those with grade 2 angles, PAS were seen in between 8% of eyes. In eyes with grade 1 angles, the rate rose to 17% in Chinese Singaporeans, and 31% in Mongolians. The odds of PAS were higher in people with narrower angles. However, there was a greater absolute number of people with PAS whose drainage angles were classified as "not occludable" than those classified "occludable."
  
  
  CONCLUSIONS
  The traditional view that primary angle closure becomes a significant possibility in drainage angles of < or = grade 2 (approximately 20 degrees ) is valid in east Asians. The definition of an "occludable" angle examined here excludes many people with PAS. This probably serves to underemphasise the role of PAC in population surveys of glaucoma prevalence in Asian people.
authors.affiliation: Singapore National Eye Centre and Singapore Eye Research Institute, Singapore.
authors.forename: P J
authors.initials: PJ
authors.lastname: Foster
authors.forename: T
authors.initials: T
authors.lastname: Aung
authors.forename: W P
authors.initials: WP
authors.lastname: Nolan
authors.forename: D
authors.initials: D
authors.lastname: Machin
authors.forename: J
authors.initials: J
authors.lastname: Baasanhu
authors.forename: P T
authors.initials: PT
authors.lastname: Khaw
authors.forename: P-H
authors.initials: PH
authors.lastname: Alsbirk
authors.forename: P S
authors.initials: PS
authors.lastname: Lee
authors.forename: S K L
authors.initials: SK
authors.lastname: Seah
authors.forename: G J
authors.initials: GJ
authors.lastname: Johnson
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D002681:China / Q000208:ethnology; D005260:Female; D005902:Glaucoma, Open-Angle / Q000175:diagnosis* / Q000208:ethnology*; D006068:Gonioscopy; D006801:Humans; D015994:Incidence; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D008986:Mongolia; D011237:Predictive Value of Tests; D012307:Risk Factors; D017678:Sex Distribution; D012846:Singapore