Finite element model of capsular bag contraction and its effect on IOL position

In cataract surgery, once the cataractous lens is removed, an intraocular lens (IOL) is inserted into the capsular bag. After surgery, some patients may experience fibrosis that can lead to capsule contraction. Typically, only part(s) of the capsular bag exhibit(s) fibrosis and subsequent contraction of the capsule. The capsular contraction exerts a mechanical effect on the IOL that affects its position that can be quantified using modelling techniques. This study presents a simplified finite element model consisting of the capsular bag, intraocular lens, and zonular forces to simulate capsular fibrosis following cataract surgery. The model was used to simulate contractions of up to 20 % in various regions of the capsular bag and evaluate the biomechanical stability of the IOL, including lens decentration, tilt, and rotation. Capsular bag contractions of 20 % resulted in IOL decentrations between 0.34 mm and 0.51 mm, and tilts between 0.48° and 3.5°. The direction of the decentration and tilt was related to the location of the region being contracted. IOL rotations ranged between 1.6° and 7.8°, which could affect the effectiveness of the astigmatic correction in Toric IOLs. Capsular contraction affecting both the anterior and posterior capsule caused the largest decentration, while contraction in areas distant from the haptic resulted in the most significant amounts of IOL tilt. The IOL centration, tilt, and orientation depend considerably on the regions being contracted and the amount of contraction. This result may be used to improve the mechanical stability of IOLs in response to capsular contraction.