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S. D. Smith, J. See, L. Aguiar, T. Aung, W. P. Nolan, D. S. Friedman, S. Radhakrishnan, Z. Ce, P. T. K. Chew; Quantitative Analysis of Iris Curvature Using Anterior Segment OCT in Patients Undergoing Laser Peripheral Iridotomy. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4544.
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To quantify iris curvature (IC) in eyes with primary angle-closure (PAC) before and after laser peripheral iridotomy (LPI).
Horizontally oriented anterior segment optical coherence tomography (AS-OCT) images were obtained of patients with PAC before and after LPI in both dark and light using a prototype instrument. Gonioscopy was performed by an experienced observer. Image analysis software was used to identify the boundaries of the anterior chamber and statistical software was used to perform least-squares regression to estimate 5th order polynomial functions describing the cornea, iris, and lens surfaces. Point-wise values of the IC (= 1/radius of curvature, with negative values representing convex up contour) of the anterior surface of the nasal and temporal iris were computed based upon the 1st and 2nd derivatives of the respective polynomials. IC was evaluated graphically (Figure), and the mean curvature values were compared before and after LPI.
Images were obtained of 9 patients (17 eyes). The median Shaffer grade was 0 or 1 in all quadrants. A significant change in IC with flattening of the iris was observed in the both quadrants of left eyes under all lighting conditions and in right eyes in the nasal quadrant in the light (all p<0.04, Wilcoxon matched-pairs signed rank test). Including images obtained in both light and dark, a reduction of IC was seen in 29/34 quadrants evaluated.
Quantitative analysis of IC is feasible using images obtained by AS-OCT. IC decreases following LPI in most patients with PAC, and likely reflects elimination of pupillary block. Evaluation of this parameter may offer insight into the mechanism of angle closure in individual patients.
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