Structural changes of vitreous humor under enzymatic activity: an in situ rheological study
The vitreous humor is a clear gel with complex fluid characteristics that occupies more than two thirds of the eye globe volume. Recently vitreous structure and the connection between its characteristics and vitreoretinal diseases have drawn significant attention. However, the fluid properties of the vitreous gel and its degeneration remain poorly understood. Reported experimental studies are aggressive for the structure of the vitreous and can affect the results drastically. Hence a less invasive method can provide results with minimized alterations to the structure of the vitreous. In addition, a method that does not require dissection of the vitreous provides the opportunity for time dependent studies.
A better understanding of the complex structure and behavior of the vitreous gel and their changes during aging and various diseases such as diabetes can lead to improvements in current treatments. This knowledge can also help with the development of new therapeutic options, both surgical and pharmaceutical, for a variety of vitreoretinal conditions. Moreover, studying the connection between the macromolecular structure of the vitreous and its fluid properties can shed light on the pathobiology of vitreoretinal diseases, which may lead to the advancement of preventive care.
Rheological methods are commonly used to study the properties of complex fluids. However, it is not possible to avoid damages to the delicate structure of the vitreous gel using traditional shear rheological methods. The purpose of this study is to use a novel in situ rheological technique to measure the viscoelastic properties of the vitreous humor gel. In addition, we quantify the impact of enzyme activity on the vitreous humor structure over time to understand the caused changes in the mechanical characteristics of the vitreous. The viscoelastic behavior of vitreous gel is due to the presence of different biopolymers in its structure. In particular, fluid properties of the vitreous are directly related to the interaction of the fluid characteristics of collagen type II and hyaluronic acid networks. We studied the effects of collagenase type II on the vitreous in comparison with a control group using the in situ method. Furthermore, we analyzed the behavior of each component over time in both groups using mechanical analogies. We ran statistical analyses between the two groups to compare the changes in the collagen network characteristics over time. The results of analysis from individual components are in agreement with the results on the changes within the vitreous network in its entirety.