title: New considerations on pupillary block mechanism.
abstract: OBJECTIVE
  To study the mechanisms of pupillary block in eyes with occludable angle by ultrasound biomicroscopy.
  
  
  METHODS
  Initially, a pilot study of 13 eyes with acute primary angle-closure without medication was executed. Ultrasound biomicroscopy measurements of the angle, posterior chamber depth and iris thickness were performed in the temporal quadrant under light and dark conditions. Afterwards, ultrasound biomicroscopy measurements of iris-lens contact distance and iris-lens angle in the temporal quadrant and central anterior chamber depth were made in 32 eyes with acute primary angle-closure or intermittent primary angle-closure without medication, under light and dark conditions before and after laser peripheral iridectomy.
  
  
  RESULTS
  In the pilot study, a significant decrease in the angle as well as a significant increase in the iris thickness occurred when comparing light to dark conditions. Before and after laser peripheral iridectomy (second study), significant differences were found in iris-lens contact distance (P<0.001) and iris-lens angle (P<0.001) under light and dark conditions. Also, significant differences were found in light and dark conditions, before laser peripheral iridectomy, in iris-lens angle (P=0.005), and after laser peripheral iridectomy, in iris-lens contact distance (P<0.001). No significant change occurred with anterior chamber depth.
  
  
  CONCLUSIONS
  A decreased angle was correlated to an increase in iris thickness. After laser peripheral iridectomy, acute primary angle-closure or primary angle-closure eyes had an increased iris-lens contact distance and a decreased iris-lens angle. The anterior chamber depth did not change. These findings contradict the theory that pupillary block is the mechanism of acute primary angle-closure.
authors.affiliation: Federal University of Minas Gerais School of Medicine - Belo Horizonte (MG) - Brazil. cronem@task.com.br
authors.forename: Sebastião
authors.initials: S
authors.lastname: Cronemberger
authors.forename: Nassim
authors.initials: N
authors.lastname: Calixto
authors.forename: André Oliveira
authors.initials: AO
authors.lastname: de Andrade
authors.forename: Rafael Vidal
authors.initials: RV
authors.lastname: Mérula
mesh_terms: D000208:Acute Disease; D005260:Female; D015812:Glaucoma, Angle-Closure / Q000000981:diagnostic imaging* / Q000209:etiology; D006801:Humans; D008297:Male; D033401:Microscopy, Acoustic; D008875:Middle Aged; D010865:Pilot Projects; D011681:Pupil Disorders / Q000150:complications / Q000000981:diagnostic imaging*