Soluble and Collagen Fiber–Associated Proteins
Many proteins remain in solution after the collagen fibers and other insoluble elements present in the vitreous gel are removed by filtration or centrifugation. Serum albumin is the major soluble vitreous protein, followed by transferrin. Other proteins include neutrophil elastase inhibitor (which may play a role in resisting neovascularization) and tissue plasminogen activator (which may have a fibrinolytic role in the event of vitreous hemorrhage). The concentration of serum proteins in the vitreous gel depends on the integrity of the retinal vasculature and the degree of intraocular inflammation. Consequently, if the blood–ocular barrier is compromised, the concentration of soluble proteins within the vitreous cavity can rise dramatically.
Some structural proteins are specifically associated with the collagen fibers. These include a leucine-rich repeat glycoprotein called opticin, which is produced in the posterior nonpigmented ciliary epithelium (NPE), and another glycoprotein called VIT1. Both opticin and VIT1 are thought to play key roles in the structure of collagen fibers and to interact with proteoglycans within the vitreous.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.