Optical Coherence Tomography Quantitative Analysis of Iris Volume Changes after Pharmacologic Mydriasis
Received 25 May 2009; received in revised form 13 October 2009; accepted 13 October 2009. published online 17 November 2009.
Purpose
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.
Design
Cross-sectional study.
Participants
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.
Main Outcome Measures
Iris volume, pupil diameter, angle configuration including angle opening distance at 500 μm (AOD 500) and trabecular–iris space at 500 μm (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 mm3 and 44.29±3.9 mm3 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 mm3 to 49.92±2.9 mm3; P<0.01), whereas it decreased significantly in the open-angle eyes (from 44.29±3.9 mm3 to 37.88±2.2 mm3; 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.
Financial Disclosure(s)
The author(s) have no proprietary or commercial interest in any materials discussed in this article.
Available online: November 17, 2009.
Department of Ophthalmology, Edouard Herriot Hospital, Lyon 1 University, Lyon, France
Correspondence: Florent Aptel, MD, MSc, Department of Ophthalmology, Edouard Herriot Hospital, 5, place d'Arsonval, 69437 Lyon Cedex 03, France
Manuscript no. 2009-696.
Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article.
ABSTRACT