Insight into vitreous biomechanics and clinical implications: A systematic review

Purpose: This systematic review investigates the current landscape of rheometric techniques used to study the viscosity and viscoelastic properties of vitreous humor to better understand vitreous behavior for clinical applications, particularly in anomalous posterior vitreous detachment (PVD). Methods: A comprehensive literature search was conducted in PubMed, EMBASE, and Scopus using the keywords "vitreous body," "viscosity," and "rheology." The review followed PRISMA guidelines, including studies assessing vitreous viscosity in human or animal eyes with experimental methods. Non-peer-reviewed and non-English studies were excluded. The quality of the 42 studies selected was assessed using the SYRCLE and adapted Newcastle-Ottawa Scale (NOS) tools. Rheometric devices, experimental models, and outcomes were analyzed. Results: The 42 studies analyzed 1,125 experimental eyes, including porcine (33.3%), bovine (25%), and human (15%) eyes. Various devices were used for experimentation with capillary tubes (20%) and rotational devices (15%) being most common. Mechanical properties such as G' and G" were reported in 10 and 8 studies, respectively. Steady-state viscosity (nss) was reported in 15 studies, values ranging from 1.43 x 10^5 +/- 2.19 x 10^4 Pa x s to 12.3 +/- 0.94 Pa x s across studies. Conclusions: This systematic review highlights variability in rheometric methods with species, techniques, and outcomes to assess vitreous humor. Standardized methods are necessary to assess vitreous properties and for clinical application.