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Matthew Wojcik, Anup Pant, Priyanka Gogte, Allie Stanley, Chidiebere Aninweze, Syril K Dorairaj, Vanita Pathak-Ray, Rouzbeh Amini; Iris incompressibility in Indian patients with occludable angles post laser peripheral iridotomy. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2087.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies have shown that the iris is less compressible in angle closure glaucoma patients (Ophthalmology, 117:3–10). Using a theoretical model, we have shown that incompressible irides crowd into the anterior chamber angle independent of the commonly known culprit, i.e. the pupillary block phenomenon (IOVS, 54:2977-84). In this study, we examined dilation-induced changes in the iris biometrics in patients with occludable angles who had undergone laser peripheral iridotomy (LPI).
Anterior segment cross-sectional images were taken at eight different clock-hours under standard and dim lighting conditions using a Visante anterior segment optical coherence tomography device (Carl Zeiss Meditec, Inc., Dublin, CA) in LV Prasad Eye Institute in Hyderabad, India. Two groups of eyes were scanned: (i) patients with occludable angles who had undergone LPI (n=20) and (ii) a healthy control group (n=10). An internally-developed software was used to quantify fifteen anterior segment biometric parameters in these images. Paired Student ttest was performed to find significant difference between the light and dim conditions in different groups.
In both groups, the pupil diameter changed significantly confirming the response of the iris constituent muscles to the changes in the ambient light (P<0.05, Fig 1a). In the control group, the iris volume significantly decreased from 62.20 ± 4.24 mm3 (mean ± standard deviation) under standard light to 59.05 ± 2.41 mm3 under dim light (p <0.05). The iris concavity also increased significantly from 0.220 ± 0.0563 mm under dim light to 0.243 ± 0.0560 mm under standard light in the control group (p <0.05). However, no significant difference was found for the same two parameters in the post-LPI group (p > 0.05).
Consistent with previous studies in angle closure glaucoma patients, we observed that patients with occludable angles have less compressible irides. One could postulate that crowding of the iris periphery during dilation causes the narrowing of the angle in such patient groups. Since LPI equalizes the pressure between the anterior and posterior chambers, one could conclude that in these patients iris tissue properties (e.g. incompressibility) play more dominant roles than the increased aqueous humor pressure on the posterior side of the iris due to pupillary block.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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