Mathematical Modelling Of The Mechanics Of Iris Buckling With Floppy Iris Leading To Angle Closure In DSEK

1. David Lockington¹
2. Xiaoyu Luo²
3. Nick Hill²
4. Kanna Ramaesh¹

¹Tennent Institute of Ophthalmology, Glasgow, UK
²Department of Mathematics, University of Glasgow, UK

Purpose: Floppy iris syndrome has been shown to complicate cataract surgery. We report similar behaviour during DSEK leading to intra-operative angle closure. We discuss the mechanics of abnormal iris behaviour in this setting.

Methods: 1. Discussion of retrospective case report
2. Mathematical modelling of floppy iris and use of energy formulae to explain novel concept of 'iris buckling'.

Results: 2 patients were observed to have floppy iris properties (miosis, billowing, prolapse) during DSEK. This led to intra-operative angle closure in 1 case despite the use of surgical iridectomy. Assessment of forces competing at pupil margin following intracameral injection of air bubble can be evaluated by energy formulae. If an iris has abnormal properties, it will buckle into a wavy mode if the external loading exceeds a critical value.

Conclusions: Energy formulae suggest a critical value of pressure exists to maintain anterior chamber stability. This critical value is lowered if iris tissue is less rigid (lower Young's modulus) or if floppy iris alters geometry leading to iris buckling. [See Figure of energy formulae]
Angle closure post DSEK has been reported on the first postoperative day, dependent on the location of the air to the iris. We believe both anterior and posterior mechanisms occurred intraoperatively in this scenario due to the floppy iris. We predict an increase in these complications due to increasing use of alpha blockers.