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Title: Modelling floppy iris syndrome and the impact of pupil size and ring devices on iris displacement
Authors: Lockington, D
Wang, ZK 
Qi, N
Malyugin, B
Cai, L
Wang, CL 
Tang, H 
Ramaesh, K
Luo, XY
Issue Date: Dec-2020
Source: Eye, Dec. 2020, v. 34, no. 12, p. 2227-2234
Abstract: Introduction The aim of this paper was to further develop a previously described finite element model which equates clinical iris billowing movements with mechanical buckling behaviour, simulating floppy iris syndrome. We wished to evaluate the impact of pupil dilation and mechanical devices on normal iris and floppy iris models. Methods Theoretical mathematical modelling and computer simulations were used to assess billowing/buckling patterns of the iris under loading pressures for the undilated and dilated normal iris, the undilated and dilated floppy iris, and additionally with a mechanical ring device. Results For the normal iris, billowing/buckling occurred at a critical pressure of 19.92 mmHg for 5 mm pupil size, which increased to 28.00 mmHg (40.56%) with a 7 mm pupil. The Malyugin ring device significantly increased critical initiating buckling pressures in the normal iris scenario, to 34.58 mmHg (73.59%) for 7 mm ring with boundary conditions I (BC I) and 34.51 mmHg (73.24%) with BC II. For the most floppy iris modelling (40% degradation), initiating buckling value was 18.04 mmHg (-9.44%), which increased to 28.39 mmHg (42.52%) with the 7 mm ring. These results were much greater than for normal undilated iris without restrictive mechanical expansion (19.92 mmHg). Conclusion This simulation demonstrates that pupil expansion devices inhibit iris billowing even in the setting of floppy iris syndrome. Our work also provides a model to further investigate the impact of pupil size or pharmacological interventions on anterior segment conditions affected by iris position.
Publisher: Nature Publishing Group
Journal: Eye 
ISSN: 0950-222X
EISSN: 1476-5454
DOI: 10.1038/s41433-020-0782-7
Rights: © 2021 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Ain Shams University. This is an open access article under the CC BY-NC-ND license (
The following publication Lockington, D., Wang, Z., Qi, N., Malyugin, B., Cai, L., Wang, C., . . . Luo, X. (2020). Modelling floppy iris syndrome and the impact of pupil size and ring devices on iris displacement. Eye (Basingstoke), 34(12), 2227-2234 is available at
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