A mathematical and computer simulation model of floppy iris syndrome and the impact of pupil size and ring devices on iris displacement

Session Details

Session Title: Cataract
Session Date/Time: Saturday 16/02/2019 | 08:30-11:00
Paper Time: 09:54
Venue: Hall Trianti

First Author: D.Lockington UK
Co Author(s): Z. Wang  N. Qi  B. Malyugin  C. Wang  H. Tang  K. Ramaesh   

Abstract Details

Purpose:

Pupil expansion devices can address inadequate pupil dilation in cataract surgery. We have previously described a finite element model for floppy iris syndrome, and simulated the impact of phenylephrine. We wished to develop this work through evaluating the impact of dilation and the Malyugin ring on iris behaviour through mathematical modeling and computer simulation.

Setting:

Tennent Institute of Ophthalmology, Glasgow, UK; Department of Mechanical Engineering, Hong Kong Polytechnic University, Hong Kong; Institute of Marine Science and Technology, Shandong University, China; Fyodorov Eye Microsurgery Federal State Institution, Moscow, Russia; School of Mathematics and Statistics, University of Glasgow, Glasgow, UK.

Methods:

Using mathematical modelling and computer simulation, we considered the stability of an iris structure under a uniform pressure, and applied a dilated central pupil parameter with 8 points of fixation at 6.25mm and 7mm diameters. We then modeled reduced iris parameters (Young’s modulus) to investigate if floppy iris tissue altered the effectiveness of the expansion device.

Results:

We refined a mathematical model of normal iris movement in the undilated and dilated forms, and created a computer simulation consistent with floppy iris syndrome (demonstrating the potential for iris displacement). Critical pressure required to initiate buckling (billowing) increased with dilation in normal conditions. Both Malyugin ring sizes were effective in preventing abnormal iris movement, even when modelling a floppy iris simulation with 40% degradation of its’ elastic properties. The 7mm Malyugin ring was more effective due to greater pupil diameter (increase of 32% versus 28% for 6.25mm ring).

Conclusions:

This study demonstrates via mathematical modeling and computer simulation that pupil expansion devices inhibit iris buckling (billowing) even in the setting of floppy iris syndrome due to mechanical dilation. Our work also provides a model to further investigate the impact of pupil dilation or pharmacological interventions on anterior segment conditions affected by iris position.

Financial Disclosure:

... gains financially from product or procedure presented