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Rouzbeh Amini, Anup Pant, Priyanka Gogte, Syril K Dorairaj, Vanita Pathak-Ray; Iris mechanical stiffness calculated using an in-vivo imaged-based finite element method in Indian patients with occludable angles post laser peripheral iridotomy. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3151. doi: https://doi.org/.
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Ex-vivo studies have shown that the iris is mechanically stiffer in patients suffering from angle closure glaucoma (IOVS, 2015 May: 6139). The in-vivo tissue responses, however, differ from ex-vivo ones, and ex-vivo measurements are severely limited for diagnosis and treatment development. To bridge this knowledge gap, we developed a method to calculate the iris stiffness using in-vivo imaging and computer simulation both in glaucomatous eyes and in healthy control ones.
Anterior segment optical coherence tomography (Carl Zeiss Meditec, Inc., Dublin, CA) images were acquired from Indian patients with occludable angles (n=8) who had undergone peripheral laser iridotomy (LPI) for angle closure and in healthy volunteers (n=8) at LV Prasad Eye Institute in Hyderabad, India. Images were taken in standard light and following pharmacologically induced dilation. An axis symmetric model of the iris based on our previous finite element model (IOVS, 53: 1188-1194) was constructed. A thin layer of the dilator muscle (8.5µm) was identified in the model and the corresponding dilator stress was applied. An inverse modeling approach (J. Global. Optim., 11: 341–359) was used to calculate iris elastic modulus (E), a metric for iris stiffness. The simulations were performed on an HP Intel Xeon machine at the Ohio Supercomputing Center (Columbus, OH).
The iris elastic modulus in healthy eyes was 2.05 ± 0.73 kPa (mean ± standard error). However, in patients with occludable angles who had undergone LPI, the iris was significantly stiffer with much higher elastic modulus value of 9.86 ± 3.71 kPa (Figure 1, p <0.05, Student t test).
Previous studies have attributed parameters contributing to the dynamic deformation of the iris (e.g. compressibility) as risk factors for glaucoma (J Glaucoma, 18:173–179; Ophthalmology, 117:3–10). In this work, we showed that in-vivo iris stiffness is potentially another parameter significantly different in patients with the history of angle closure glaucoma. Since our proposed study is a non-invasive procedure, it has the potential to become a new diagnostic method following further studies in different patient populations.
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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