title: In vivo analysis of vectors involved in pupil constriction in Chinese subjects with angle closure.
abstract: OBJECTIVE
  To evaluate the acceleration of pupil constriction (APC) in response to illumination using video anterior segment optical coherence tomography (AS-OCT) in angle closure and normal eyes.
  
  
  METHODS
  This was an observational study of 342 Chinese subjects. Iris and angle changes in response to illumination were captured with real-time video recordings of AS-OCT and analyzed frame by frame. APC was calculated using a quadratic function, fitting pupil diameter to a time series. APC was divided into two vector components: acceleration of pupil block (APB) acting perpendicular to the lens surface and acceleration of iris stretch (AIS) acting toward the iris root.
  
  
  RESULTS
  Of 342 eligible patients, 306 (89.5%) were available for analysis; of whom 136 (41.7%) had angle closure. After adjusting for age, sex, baseline pupil diameter, and iris thickness, APC was significantly lower in angle closure eyes (0.61 mm/s(2)) than in open-angle eyes (0.90 mm/s(2)) (P < 0.0001) as was AIS (0.58 mm/s(2) vs. 0.89 mm/s(2)) (P < 0.001). APB was significantly higher in angle closure eyes compared to open-angle eyes (0.14 mm/s(2) vs. 0.09 mm/s(2)) (P < 0.001). After adjusting for age and sex in logistic regression, the magnitude and direction of all vector parameters were significantly associated with presence of angle closure.
  
  
  CONCLUSIONS
  Angle closure eyes have smaller AIS and larger APB in response to illumination as measured using AS-OCT videography. This shows that, comparatively, the iris of angle closure eyes stretches less and develops a more convex configuration in response to illumination.
authors.affiliation: Singapore Eye Research Institute at the Singapore National Eye Centre, Singapore, Republic of Singapore.
authors.forename: Ce
authors.initials: C
authors.lastname: Zheng
authors.forename: Carol Y
authors.initials: CY
authors.lastname: Cheung
authors.forename: Tin
authors.initials: T
authors.lastname: Aung
authors.forename: Arun
authors.initials: A
authors.lastname: Narayanaswamy
authors.forename: Sim-Heng
authors.initials: SH
authors.lastname: Ong
authors.forename: David S
authors.initials: DS
authors.lastname: Friedman
authors.forename: John C
authors.initials: JC
authors.lastname: Allen
authors.forename: Mani
authors.initials: M
authors.lastname: Baskaran
authors.forename: Paul T
authors.initials: PT
authors.lastname: Chew
authors.forename: Shamira A
authors.initials: SA
authors.lastname: Perera
mesh_terms: D000869:Anterior Eye Segment; D044466:Asian People / Q000208:ethnology; D001699:Biometry; D002681:China / Q000453:epidemiology; D005260:Female; D015812:Glaucoma, Angle-Closure / Q000208:ethnology / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D007429:Intraocular Pressure; D032801:Iridectomy; D008027:Light; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011680:Pupil / Q000528:radiation effects*; D012025:Reflex, Pupillary / Q000502:physiology*; D041623:Tomography, Optical Coherence; D014741:Video Recording