Abstract
IntroductionThe 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.MethodsTheoretical 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.ResultsFor 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).ConclusionThis 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.
Highlights
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
With undilated pupil With pupil dilated to 7 mm With 7 mm M-ring (BC I) With 7 mm M-ring (BC II)
The dynamic coupled characteristics of the iris and the aqueous humour flow has been previously analysed by Heys et al, and presented as a mathematical model to predict the iris deformation mechanics [27]
Summary
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. Femtosecond laser cataract surgery has been associated with the release of prostaglandins into the aqueous humour and subsequent pupillary constriction and it has been reported that up to 10% of cases of inadequate pupillary dilatation will still need mechanical pupil expansion, using adjuncts such as iris hooks or ring devices [10,11,12]. One such device is the popular Malyugin ring (MicroSurgical Technology Inc., Redmond, Washington, USA), which was launched in 2007. It has four circular scrolls located at equidistant points on the ring to allow eight iris-retaining points of attachment, stabilising the central pupil margin and limiting abnormal iris movement, with the second version providing a fixed 7 mm pupil opening [13,14,15]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
