title: Iris cross-sectional area decreases with pupil dilation and its dynamic behavior is a risk factor in angle closure.
abstract: OBJECTIVE
  To estimate the change in iris cross-sectional (CS) area with pupil dilation using anterior segment optical coherence tomography comparing eyes with angle closure (AC) to open angle glaucoma (OAG).
  
  
  METHODS
  Sixty-five patients from the Wilmer Glaucoma service, 36 with definite or suspected OAG and 29 with definite or suspected AC, underwent anterior segment optical coherence tomography imaging under 3 conditions (pupil constriction to light, physiologic dilation in the dark, and after pharmacologic dilation). The nasal and temporal iris CS areas were measured with custom software, 3 times in each of 4 meridians. The principal outcome variables were iris CS area and change in iris CS area/mm pupil diameter change. The relation of these parameters to potential variables that would influence iris area was estimated by multivariate regression.
  
  
  RESULTS
  CS area was smaller in eyes with larger pupil diameter, those that had undergone trabeculectomy, and those of European-derived persons (P<0.05 for all in a univariate analysis). In a multivariate model with CS area as the dependent variable, larger pupil diameter (with a 0.19 mm decrease in CS area for each 1 mm of pupil enlargement, P=0.0002), and trabeculectomy remained significant factors. In a second multivariate model, AC irides had less change in CS area/mm pupil enlargement than OAG or OAG suspects (P=0.01). Change in iris CS area was essentially complete in 5 seconds (n=10 eyes).
  
  
  CONCLUSIONS
  The iris loses nearly half its volume from a pupil diameter of 3 to 7 mm, probably by eliminating extracellular fluid. Smaller iris CS area change with physiologic pupil dilation is a potential risk factor for AC. Dynamic iris CS area change deserves testing as a prospective indicator of AC.
authors.affiliation: Wilmer Institute, Johns Hopkins University School of Medicine, Baltimore, MD, USA. hquigley@jhmi.edu
authors.forename: Harry A
authors.initials: HA
authors.lastname: Quigley
authors.forename: David M
authors.initials: DM
authors.lastname: Silver
authors.forename: David S
authors.initials: DS
authors.lastname: Friedman
authors.forename: Mingguang
authors.initials: M
authors.lastname: He
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Plyler
authors.forename: Charles G
authors.initials: CG
authors.lastname: Eberhart
authors.forename: Henry D
authors.initials: HD
authors.lastname: Jampel
authors.forename: Pradeep
authors.initials: P
authors.lastname: Ramulu
mesh_terms: D005260:Female; D015812:Glaucoma, Angle-Closure / Q000503:physiopathology*; D005902:Glaucoma, Open-Angle / Q000503:physiopathology; D006068:Gonioscopy; D006801:Humans; D007429:Intraocular Pressure; D007498:Iris / Q000503:physiopathology*; D008027:Light; D008297:Male; D008875:Middle Aged; D009184:Mydriatics / Q000008:administration & dosage; D009798:Ocular Hypertension / Q000503:physiopathology; D011680:Pupil / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D012307:Risk Factors; D041623:Tomography, Optical Coherence; D014065:Tonometry, Ocular
chemical_list: D009184:Mydriatics