The primary function of the lens capsule of the eye unfolds during the process of accommodation; wherein, tension imposed onto its equator is released, allowing the elastic capsule to mold the underlying lens nucleus and cortex into a more quasispherical morphology to change focus from distant to near objects. Given its highly mechanical nature, it is prudent to study the native lens capsule from the perspective of biomechanics for such applications as understanding the mechanism of accommodation. Further, cataract surgery introduces alterations to the geometry of the lens capsule that lead to changes in resident cell behavior from quiescent to contractile and synthetic. Though resultant changes in capsule histology are well documented little has been done to quantify the corresponding altered mechanics, which is important for elucidating related post-surgical pathologies and improving prosthetic lens design. In this study we present the first data on the in situ multiaxial mechanical behavior of the native and hyperglycemic anterior lens capsule in both the porcine and human models. From these data, native stresses in the lens capsule are calculated using a finite element analysis, and alterations in the corresponding strain field are calculated after the introduction of a continuous circular capsulorhexis, which is imposed during cataract surgery. Finally, we quantify both the altered mechanical behavior and contractile loads imposed onto the lens capsule after cataract surgery.

Knowledge of the mechanics of the lens capsule is crucial for improving cataract surgery as well as understanding better the physiological role of the lens capsule in the process of accommodation. Previous research on the mechanical properties of the lens capsule contains many gaps and contradictions due to experimental limitations and inappropriate assumptions. Thus, the goal of this work is to quantify fully the regional, multiaxial mechanical behavior of the lens capsule and to calculate the change in stress and strain fields as a result of cataract surgery. Determining in situ the multiaxial mechanical behavior of the lens capsule required the design and construction of an experimental device capable of altering stresses in the capsule while measuring localized surface deformations. Tests performed on this device reveal that the meridional and circumferential strains align with the principal directions and are equivalent through most of the anterior lens capsule, except close to the equator where the meridional strain is greater. Furthermore, preconditioning effects were also found to be significant. Most importantly, however, these tests provide the data necessary for calculating material properties. This experimental system is advantageous in that it allows reconstruction of 3D geometry of the lens capsule and thereby quantification of curvature changes, as well as measurement of surface deformations that result from various surgical interventions. For instance, a continuous circular capsulorhexis (CCC) is commonly used during cataract surgery to create a hole in the anterior lens capsule (typically with a diameter of 5 mm). After the introduction of a CCC, strain was found to redistribute evenly from the meridional direction (retractional strain) to the circumferential direction (extensional strain), where both directional components of strain reached magnitudes up to 20% near the edge of the CCC. Furthermore, the curvature was found to increase at the edge of the CCC and remain the same near the equator, indicating that the mere introduction of a hole in the lens capsule will alter the focal characteristics of the lens and must therefore be considered in the design of an accommodative intraocular lens.