Iris Crypts Could Reduce the Chance of Angle Closure: A Computational Biomechanics Study Derived From Clinical and Human Iris Data.

PURPOSE

To investigate the effect of crypts during pupil constriction and dilation on the potential for angle closure by performing finite element analysis using clinical and experimental data on human tissues.

METHODS

A computational model was developed to determine the influence of small crypts (surface area of ∼0.015 mm2) and large crypts (surface area of 0.300 mm2) on the anterior chamber angles during pupil dilation. The model needed permeability data from human subjects; hence, 21 enucleated human eyes (72 hours postmortem) were procured and subjected to a flow setup previously reported. Finally, 66 subjects were recruited to measure pupil constriction and dilation levels from optical coherence tomography (OCT) videos.

RESULTS

The hydraulic permeability of the human iris stroma was determined to be 2.55 ± 1.93 × 10-5 mm2/Pa · s. The average iris constriction and dilation durations were 0.710 ± 0.213 seconds and 1.24 ± 0.401 seconds, respectively, with pupil diameter changes of 1.16 ± 0.39 mm and 0.75 ± 0.27 mm, respectively. The computational models had starting anterior chamber angles of 51.30° and final anterior chamber angles of 26.81° once steady state had been reached. In an extreme case with decreased anterior border layer (ABL) permeability, the anterior chamber angle narrowed to 12.37°, but the presence of crypts kept the angle above 20.36°, highlighting the potential of crypts in preventing angle closure.

CONCLUSIONS

Our findings on the biomechanics of crypts in the iris may drive the development of novel treatments by altering ABL morphology, providing an alternative bypass for angle closure prevention in high-risk patients.