In vivo biomechanical assessment of iridial deformations and muscle contractions in human eyes

• Type of Material: Article
• Authors: Babak N Safa, Emory University; Mohammad Reza Bahrani Fard, Emory University; Christopher Ethier, Emory University
• Language: English
• Date: 2022-07-06
• Publisher: ROYAL SOC
• Publication Version: Final Published Version
• Copyright Statement: © 2022 The Authors.
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1098/rsif.2022.0108
• Title of Journal or Parent Work: JOURNAL OF THE ROYAL SOCIETY INTERFACE
• Volume: 19
• Issue: 192
• Start Page: 20220108
• End Page: 20220108
• Grant/Funding Information: We acknowledge our funding sources NIH-NEI (R01 EY031710, C.R.E.), the Georgia Research Alliance (C.R.E.) and the BrightFocus Foundation (postdoctoral fellowship G2021005F, B.N.S.).
• Keywords: Science & Technology; Multidisciplinary Sciences; pupil; glaucoma; IMAGE; IRIS MECHANICS; iris; STIFFNESS; GLAUCOMA; PUPIL SIZE; finite-element method; Science & Technology - Other Topics; digital image correlation; PARAMETERS; PRIMARY ANGLE-CLOSURE
• Research Categories: Engineering, Biomedical

Abstract

The iris is a muscular organ whose deformations can cause primary angle-closure glaucoma (PACG), a leading cause of blindness. PACG risk assessment does not consider iridial biomechanical factors, despite their expected influence on iris deformations. Here, we exploited an existing biometric dataset consisting of near-infrared movies acquired during the pupillary light reflex (PLR) as a unique resource to study iris biomechanics. The PLR caused significant (greater than 100%) and essentially spatially uniform radial strains in the iris in vivo, consistent with previous findings. Inverse finite-element modelling showed that sphincter muscle tractions were ca fivefold greater than iridial stroma stiffness (range 4- to 13-fold, depending on sphincter muscle size). This muscle traction is greater than has been previously estimated, which may be due to methodological differences and/or to different patient populations in our study (European descent) versus previous studies (Asian); the latter possibility is of particular interest due to differential incidence rates of PACG in these populations. Our methodology is fast and inexpensive and may be a useful tool in understanding biomechanical factors contributing to PACG.