Increased Iris Stiffness in Patients With a History of Angle-Closure Glaucoma: An Image-Based Inverse Modeling Analysis

Pant, Anup; Gogte, Priyanka; Pathak-Ray, Vanita; Dorairaj, Syril; Amini, Rouzbeh

doi:10.1167/iovs.18-24327

Cited by 26 publications

(37 citation statements)

References 42 publications

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“…For a given soft tissue, the density of collagen fibers typically correlates with the mechanical stiffness of such a tissue [25]. [9]. Our results are consistent with these observations, but our methodology also had the benefit to additionally assess the permeability of the iris tissue.…”

Section: Higher Tissue Stiffness In Pacg Subjectssupporting

confidence: 85%

“…The sphincter region was assumed to be electrically active, and the active force produced by the smooth muscle cells (SMCs) in the circumferential direction was defined as σactive= σ eθ⊗eθ , where σ is the magnitude of the active force and eθ is the unit circumferential vector. Following previous studies, the magnitude of σactive was assumed to be 40 kPa for both PACG and healthy eyes [9,18]. The total stress in the sphincter region was computed by adding the passive and active components, i.e., σtotal = σpassive + σactive.…”

Section: Constitutive Relationships For All Tissue Layersmentioning

confidence: 99%

“…Because of this limitation, Pant et al proposed a non-invasive in-vivo procedure to evaluate iris stiffness directly from optical coherence tomography (OCT) images [9]. While this was an important piece of work, it was limited by the assumption that the iris was an incompressible solid that could not exchange water with the anterior chamber.…”

Section: Introductionmentioning

confidence: 99%

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Changes in Iris Stiffness and Permeability in Primary Angle Closure Glaucoma

Panda

Tan

Tun

et al. 2021

Preprint

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PurposeTo evaluate the biomechanical properties of the iris by evaluating iris movement during pupil constriction and to compare such properties between healthy and primary angle-closure glaucoma (PACG) subjects.MethodsA total of 140 subjects were recruited for this study. In a dark room, the anterior segments of one eye per subject were scanned using anterior segment optical coherence tomography (AS-OCT, SS-1000 CASIA, Tomey Corporation, Nagoya, Japan) imaging during induced pupil constriction with an external white light source of 1700 lux. Using a custom segmentation code, we automatically isolated the iris segments from the AS-OCT images, which were then discretized and transformed into a three-dimensional point cloud. For each iris, a finite element (FE) mesh was constructed from the point cloud, and an inverse FE simulation was performed to match the clinically observed iris constriction in the AS-OCT images. Through this optimization process, we were able to identify the elastic modulus and permeability of each iris.ResultsFor all 140 subjects (95 healthy and 45 PACG of Indian/Chinese ethnicity, Age: 60.2±8.7 for PACG subjects and 57.7±10.1 for healthy subjects), the simulated deformation pattern of the iris during pupil constriction matched well with OCT images. We found that the iris stiffness was higher in PACG than in healthy controls (24.5±8.4 kPa vs 17.1±6.6 kPa with 40 kPa of active stress specified in the sphincter region; p < 0.001), whereas iris permeability was lower (0.41±0.2 mm2/kPa.s vs 0.55±0.2 mm2/kPa.s; p = 0.142).ConclusionThis study suggests that the biomechanical properties of the iris in PACG are different from those in healthy controls. An improved understanding of the biomechanical behavior of the iris may have implications for the understanding and management of angle-closure glaucoma.

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Section: Higher Tissue Stiffness In Pacg Subjectssupporting

confidence: 85%

Section: Constitutive Relationships For All Tissue Layersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Changes in Iris Stiffness and Permeability in Primary Angle Closure Glaucoma

Panda

Tan

Tun

et al. 2021

Preprint

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“…Zheng et al 19 reported the novel associations of a slower speed of iris constriction in eyes with angle closure as well as a lower acceleration of iris stretch, and a more convex iris configuration compared to open-angled eyes, suggesting that such differences in irido-pupillary dynamics may have a role in the pathogenesis of angle closure. Pant et al 20 evaluated in vivo iris mechanical properties using optical coherence tomography scans and image-based inverse modeling analysis. They found that the irides of patients with a history of PACG were significantly stiffer compared to healthy irides.…”

Section: Discussionmentioning

confidence: 99%

Young's Modulus Determination of Normal and Glaucomatous Human Iris

Narayanaswamy

Nai

Nongpiur

et al. 2019

Invest. Ophthalmol. Vis. Sci.

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Citation: Narayanaswamy A, Nai MH, Nongpiur ME, et al. Young's modulus determination of normal and glaucomatous human iris. Invest Ophthalmol Vis Sci. 2019;60:2690-2695. https://doi.org/10.1167/iovs.18-26455 PURPOSE. To evaluate the biomechanical properties (Young's modulus) of normal (control) and glaucomatous human iris using atomic force microscopy (AFM).METHODS. Iris tissue obtained from eighteen glaucomatous subjects (equal number of eyes with primary angle closure glaucoma (PACG) and primary open angle glaucoma (POAG) and five normal subjects who underwent elective eye surgery were subjected to the estimation of Young's modulus by AFM. Force measurements were done at room temperature using Nanowizard II BioAFM. The iris samples were immersed in the liquid media (PBS with 0.1% BSA) during force measurements. Young's modulus values were calculated for each recorded curve using JPK Data Processing Software, which uses a Hertz's contact model for spherical indenters fitted to the extend curves.

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“…The iris is also implicated in the pathophysiology of glaucoma through alterations in its biomechanical properties and fluid conductivity. 2 Altered biomechanical function of the iris exhibits itself as increased mechanical stiffness in the PACG iris, 3 , 4 which has been demonstrated in PACG irises both ex vivo 5 and in vivo, 6 in association with a reduction in iris volume/area changes in response to pupil dilation. 7 – 9 This property of the PACG iris may be correlated with increase in extracellular matrix gene expression in the iris.…”

mentioning

confidence: 99%

Altered Iris Aquaporin Expression and Aqueous Humor Osmolality in Glaucoma

Huang

Seet

et al. 2021

Invest. Ophthalmol. Vis. Sci.

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Purpose Aquaporins (AQPs) facilitate transmembrane osmotic water transport and may play a role in iris fluid conductivity, which is implicated in the pathophysiology of glaucoma. In this study, we compared the iris expression of AQPs and aqueous osmolality between primary angle closure glaucoma (PACG), primary open-angle glaucoma (POAG), and nonglaucoma eyes. Methods AQP1-5 transcripts from a cohort of 36 PACG, 34 POAG and 26 nonglaucoma irises were measured by quantitative real-time PCR. Osmolality of aqueous humor from another cohort of 49 PACG, 50 POAG, and 50 nonglaucoma eyes were measured using an osmometer. The localization of AQP1 in both glaucoma and nonglaucoma irises was determined by immunofluorescent analysis. Results Of the five AQP genes evaluated, AQP1 and AQP2 transcripts were significantly upregulated in both PACG (3.48- and 8.07-fold, respectively) and POAG (3.12- and 11.58-fold, respectively) irises relative to nonglaucoma counterparts. The aqueous osmolalities of PACG (303.68 mmol/kg) and POAG (300.79 mmol/kg) eyes were significantly lower compared to nonglaucoma eyes (312.6 mmol/kg). There was no significant difference in expression of AQP transcripts or aqueous osmolality between PACG and POAG eyes. Conclusions PACG and POAG eyes featured significant increase in AQP1 and AQP2 expression in the iris and reduced aqueous osmolality compared to nonglaucoma eyes. These findings suggest that the iris may be involved in altered aqueous humor dynamics in glaucoma pathophysiology. Because PACG did not differ from POAG in both properties studied, it is likely that they are common to glaucoma disease in general.

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Increased Iris Stiffness in Patients With a History of Angle-Closure Glaucoma: An Image-Based Inverse Modeling Analysis

Cited by 26 publications

References 42 publications

Changes in Iris Stiffness and Permeability in Primary Angle Closure Glaucoma

Changes in Iris Stiffness and Permeability in Primary Angle Closure Glaucoma

Young's Modulus Determination of Normal and Glaucomatous Human Iris

Altered Iris Aquaporin Expression and Aqueous Humor Osmolality in Glaucoma

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