title: Pupil dynamics in Chinese subjects with angle closure.
abstract: OBJECTIVE
  To evaluate the speed of pupil constriction (SPC) in response to a standardized change in illumination from dark to light using anterior segment optical coherence tomography (AS-OCT) in eyes with closed angles, compared to those with open angles.
  
  
  METHODS
  This was a prospective, comparative, observational study. Study subjects with primary angle-closure glaucoma (PACG) and/or primary angle-closure (PAC) were recruited along with a group of normal as controls. Videos of iris and anterior segment changes in response to illumination were captured with real-time video recording from AS-OCT and analysed frame by frame, beginning from a dilated to a constricted pupil. Customized software was used to measure speed of iris constriction, anterior chamber depth (ACD), anterior chamber width (ACW), iris thickness, and pupil diameter (PD). SPC was defined as the rate of pupil diameter change in response to illumination.
  
  
  RESULTS
  One hundred and sixty three Chinese subjects were recruited in this study. A total of 137 of 163 eligible videos (82.5%) were available for analysis, comprising 87 subjects with closed angles (all had undergone laser peripheral iridotomies before) and 50 with open angles. SPC was less in eyes with closed angles (1.22 mm/sec vs 1.56 mm/sec, p<0.001), after adjusting for age and ACW, and was positively correlated with axial length, ACD, anterior chamber angle status, PD in the dark, and iris thickness in the dark, (all r>0.2, all p<0.05). In multivariate analysis, SPC was independently associated with anterior chamber angle status (closed angle vs open angle) (β=0.276, p=0.016) and PD in dark (β= 0.129, p=0.009), after adjusting for age, ACW, ACD, iris thickness and vertical cup-to-disc ratio.
  
  
  CONCLUSIONS
  Compared to those with open angles, eyes with closed angles in Chinese subjects have slower speed of pupil constriction in response to dark-light change, even after adjusting for biometric factors associated with angle closure. The results suggest that differences in irido-pupillary dynamics may play a role in the pathogenesis of angle closure.
authors.affiliation: Singapore Eye Research Institute, Singapore & Singapore National Eye Centre, Singapore, Singapore.
authors.forename: Ce
authors.initials: C
authors.lastname: Zheng
authors.forename: Carol Y
authors.initials: CY
authors.lastname: Cheung
authors.forename: Arun
authors.initials: A
authors.lastname: Narayanaswamy
authors.forename: Sim-Heng
authors.initials: SH
authors.lastname: Ong
authors.forename: Shamira A
authors.initials: SA
authors.lastname: Perera
authors.forename: Mani
authors.initials: M
authors.lastname: Baskaran
authors.forename: Paul T
authors.initials: PT
authors.lastname: Chew
authors.forename: David S
authors.initials: DS
authors.lastname: Friedman
authors.forename: Tin
authors.initials: T
authors.lastname: Aung
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D044466:Asian People / Q000208:ethnology; D003623:Dark Adaptation; D005260:Female; D015812:Glaucoma, Angle-Closure / Q000208:ethnology / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D032801:Iridectomy; D007498:Iris / Q000502:physiology; 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; D014794:Visual Fields / Q000502:physiology