Ryan M. Pedrigi
Date of this Version
Ameku, K. (2022). Finite Element Modeling of the Human Lens Capsule to Characterize Evolving Mechanics after Cataract Surgery [Unpublished master's thesis]. University of Nebraska-Lincoln.
Cataract surgery is one of the most commonly performed ophthalmic procedures in the world. During surgery, a permanent hole is cut in the lens capsule, the diseased tissue is removed, and an artificial intraocular lens (IOL) is implanted. While considered highly successful, limitations remain. Mainly, most implanted IOLs are monofocal, meaning they cannot restore accommodation, the ability of the lens to change focus from distant to near vision. Attempts to design IOLs with an accommodative feature (AIOLs) have been hindered by a cellular response known as posterior capsule opacification (PCO). While improvements in implant design have decreased the rates of PCO in monofocal IOLs, it is still present and continues to progress years after surgery. Previous work has hypothesized that this errant cellular behavior is due to the change in mechanical environment introduced by cataract surgery.
Few numerical models have explored the interaction between the lens capsule and an implanted device, which is key in quantifying the changes to the mechanical environment that occur after surgery. Recent work by our group proposed the first fully 3D numerical model of the post-surgical human lens capsule with an implanted IOL and showed a highly disturbed stress field in the post-surgical model compared to native, supporting the theory of a preferred mechanical environment. Herein, this approach was extended to AIOLs by developing a new post-surgical model with an implanted AIOL, with tractions calibrated to approximate accommodation based on changes in geometry of a native lens model. The post-surgical model indicated that current AIOL designs cannot restore youthful levels of accommodation based on axial displacement measurements.
Since PCO is a chronic disease, a method to quantify changes in lens capsule mechanics years after surgery was developed by coupling the numerical model of the post-surgical lens with a growth and remodeling (G&R) framework. The results showed that implantation of an additional device called a capsular tension ring (CTR) mitigated the increases in mass production, capsule thickness, and capsule stiffness caused by the cellular response, supporting studies that have shown implantation of such a device minimizes the effects of PCO compared to an implanted IOL alone.
Advisor: Ryan M. Pedrigi