title: Optical coherence tomography quantitative analysis of iris volume changes after pharmacologic mydriasis.
abstract: OBJECTIVE
  To describe a method using anterior segment optical coherence tomography (AS OCT) for estimating iris volume. To quantify changes in iris volume induced by pharmacologic mydriasis in narrow-angle eyes predisposed to angle-closure compared with normal open-angle eyes.
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  Thirty fellow eyes of 30 patients who had an episode of primary acute angle-closure and 30 eyes of 30 normal age- and gender-matched subjects with open angles. All fellow eyes had a patent laser peripheral iridotomy.
  
  
  METHODS
  Iris volume and all biometric measurements were performed before and after instillation of 1% tropicamide and at least 1 week later 10% phenylephrine. Iris volume was estimated using AS OCT radial sections of the iris and a customized image-processing software.
  
  
  METHODS
  Iris volume, pupil diameter, angle configuration including angle opening distance at 500 mum (AOD 500) and trabecular-iris space at 500 mum (TISA 500), AS OCT anterior chamber depth, and A-scan ultrasonography axial length before and after pupil dilation.
  
  
  RESULTS
  Iris volumes measured before dilation of the pupil were 44.94+/-2.1 mm(3) and 44.29+/-3.9 mm(3) in the fellow eyes and open-angle eyes, respectively, which was not significantly different (P>0.1). Thirty minutes after instillation of 1% tropicamide, mean iris volume increased significantly in the fellow eyes (from 44.94+/-2.1 mm(3) to 49.92+/-2.9 mm(3); P<0.01), whereas it decreased significantly in the open-angle eyes (from 44.29+/-3.9 mm(3) to 37.88+/-2.2 mm(3); P<0.01). Similar changes were observed after instillation of 10% phenylephrine. Based on multivariate analysis, significant predictors of increase in iris volume after pupil dilation were eyes predisposed to angle-closure compared with open-angle eyes (P = 0.008), larger pupil diameter (P = 0.02), and brown eyes (P = 0.01). Relative iris volume increase was correlated significantly with AOD 500 and TISA 500 relative decrease in the narrow-angle group (P<0.05).
  
  
  CONCLUSIONS
  The iris volume may be estimated with AS OCT. The iris volume increases after pupil dilation in narrow-angle eyes predisposed to acute angle closure. In those patients, this biometric change is associated with a narrowing of the angle despite a patent laser peripheral iridotomy.
  
  
  BACKGROUND
  The author(s) have no proprietary or commercial interest in any materials discussed in this article.
authors.affiliation: Department of Ophthalmology, Edouard Herriot Hospital, Lyon 1 University, Lyon, France.
authors.forename: Florent
authors.initials: F
authors.lastname: Aptel
authors.forename: Philippe
authors.initials: P
authors.lastname: Denis
mesh_terms: D000208:Acute Disease; D000368:Aged; D003430:Cross-Sectional Studies; D004108:Dilatation, Pathologic; D005260:Female; D015812:Glaucoma, Angle-Closure / Q000175:diagnosis* / Q000209:etiology; D005902:Glaucoma, Open-Angle / Q000175:diagnosis; D006068:Gonioscopy; D006801:Humans; D007429:Intraocular Pressure; D007498:Iris / Q000000981:diagnostic imaging / Q000473:pathology*; D008297:Male; D033401:Microscopy, Acoustic; D009184:Mydriatics / Q000008:administration & dosage*; D010656:Phenylephrine; D011446:Prospective Studies; D011680:Pupil / Q000187:drug effects*; D012307:Risk Factors; D041623:Tomography, Optical Coherence; D014331:Tropicamide / Q000008:administration & dosage
chemical_list: D009184:Mydriatics; D010656:Phenylephrine; D014331:Tropicamide