Rheology and hydraulic fracture in cataract surgery

Abstract

Cataracts are responsible for almost half of worldwide blindness, making it one of the biggest health challenges in this era. Cataracts are irreversible because of their pathology, which is controlled by the aging and biochemical change of eye tissues. As a result cataract surgery is currently the only effective treatment. The general procedure of cataract surgery includes separation and removal of the failed lens tissue from the surrounding soft tissue in the eye, followed by artificial lens implantation. Lens removal requires successful separation of lens tissues as a critical step that determines surgical success. However key parts of cataract separation affected by fluid mechanics and rheology are uncharacterised. This project aims to explain the behaviors of such separation phenomena and connect fundamentals with possible explanations and enhancements.

A multi-layer bio-polymer injection model is developed to mimic the separation process in cataract surgeries. The separation can be considered peeling of a soft elastic tissue by a pressure-driven fluid flow, whose performance is closely related to properties such as flow rate and velocity as well as fluid viscosity, normal stress and yield stress. In our project, the separation physics is studied as a hydraulic fracture problem. Theories are proposed to discuss the effectiveness and safety of hydraulic fracture with different flow and fluid parameters. It is found both higher flow rate and viscosity will cause tissue to be deformed more, which may increase the risks of tissue damage. Yield stress fluids with significant elasticity are not suitable as in most cases they rupture the tissue. Normal stress fluids have the potential to provide safe and effective separation. It is found that with a small scale separation, however, the separation effectiveness is mainly affected by the flow rate, and the fluid properties play a more minor role. General ideas and potential improvements according to our results and theories are also proposed for cataract surgeries, which we hope will contribute to easier and safer separation.