Abstract
Purpose :
To use finite element (FE) analysis to assess what morphological and biomechanical factors of the Iris and of the Anterior Chamber (AC) are more likely to trigger angle closure during pupil dilation.
Methods :
The study consisted of 1,344 FE models (Figure 1) comprising of the cornea, sclera, lens and iris (stroma, sphincter and dilator tissues) to simulate pupil dilation and to assess changes in angle. For each model, we varied the following parameters: the AC depth (ACD) and width (ACW), iris convexity (IC), thickness (IT), stiffness (E) and Poisson’s ratio (v), with all possible combinations of the parameters ACD = 2, 3 & 4 mm, ACW = 10, 11 & 12 mm, IC = 0, 0.1, 0.2, 0.3 mm, IT = 0.3, 0.4 & 0.5 mm, E = 3, 4, 5 & 6 kPa and v = 0, 0.1, 0.2 & 0.3. All models simulated a dilator muscle contractile force of 40 kPa, and all exhibited an initial pupil diameter of 4 mm. A zero-friction sliding interface was enforced between the lens and the iris and the AC angle was measured. We evaluated for the change in AC angle (△∠) and the final dilated AC angles (∠f) from baseline to dilation for each parameter.
Results :
The parameters that influenced angle closure the most were ACD, ACW, IT and v (Table 1). With decreasing ACD, we observed smaller changes in AC angle, but the final angles also remained smaller (∠f = 63.9°±10.2°, 52.6°±11.5° and 36.1°±11.4° for ACD = 4mm, 3mm and 2mm respectively). For IT, △∠ increased by +9.7°±3.9° when IT increased from 3 to 4mm, and +9.4°±3.7° when IT increased from 4 to 5mm, resulting in decreased ∠f. A smaller ACW and larger v were both attributed to closing of the AC angle, with the former resulting in a larger change in ∠f. Interestingly, IC showed an inverse relationship to expected outcomes, with a larger convexity resulting in smaller △∠ and ∠f. The stiffness of the iris (E) was not found to be of significance in angle closure, possibly in part from less dilation at higher stiffness values.
Conclusions :
We performed a parametric computational study to better understand what morphological and biomechanical factors (and their interactions) of the iris and of the AC could trigger angle closure. Our study was performed with ‘hypothetical’ patients, but could be combined with optical coherence tomography imaging in a clinical scenario to better identify the patients at risks of developing angle closure.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.