- The vitreous humor, also known as the vitreous body, is a clear, gel-like substance that fills the posterior chamber of the eye, occupying the space between the lens and the retina.
- It comprises about 80% of the eye’s total volume and plays a crucial role in maintaining the shape of the eye, supporting the retina, and allowing the unobstructed passage of light to the photoreceptor cells. Unlike the continuously circulating aqueous humor in the anterior segment, the vitreous humor is relatively static and is not replenished during life.
- Structurally, the vitreous humor is composed of about 99% water, with the remaining 1% consisting of collagen fibrils, hyaluronic acid, proteins, and small amounts of salts and sugars. Despite its high water content, the presence of these macromolecules gives it a gelatinous consistency. The collagen and hyaluronic acid are organized in a way that maintains optical clarity while providing structural support. The vitreous is enclosed by a thin membrane called the vitreous cortex, which interfaces with the retina and other internal ocular structures.
- Functionally, the vitreous humor acts as a shock absorber, protecting the delicate retinal tissue from sudden eye movements or trauma. It also helps to hold the retina in place by pressing it gently against the choroid, ensuring proper alignment with the lens for focused vision. Additionally, it serves as a light-transmitting medium, allowing photons to pass through without distortion on their way to the retina. The vitreous is virtually free of cells and blood vessels, which contributes to its transparency, essential for sharp vision.
- Over time, especially with aging, the vitreous humor can undergo liquefaction in a process called vitreous syneresis. This results in the formation of small clumps or strands of collagen, which may cast shadows on the retina and be perceived as floaters—tiny specks or cobweb-like shapes in the field of vision. In some cases, the vitreous can detach from the retina, a condition known as posterior vitreous detachment (PVD). While often benign, PVD can sometimes lead to retinal tears or retinal detachment, which are sight-threatening emergencies requiring prompt treatment.
- The vitreous can also be affected by pathological conditions such as vitreous hemorrhage, where blood leaks into the gel due to retinal vessel damage, often related to diabetic retinopathy, trauma, or retinal vein occlusion. Inflammatory diseases like uveitis may lead to clouding of the vitreous, further impairing vision. When the vitreous becomes severely clouded or contains blood, vitrectomy surgery may be performed to remove it and restore visual clarity.
- Unlike the aqueous humor, the vitreous does not have a regenerative capacity or an active drainage system, making it more vulnerable to long-term changes and less accessible for therapeutic interventions. However, research into drug delivery via the vitreous cavity (intravitreal injections) has led to advances in treating conditions like wet age-related macular degeneration, diabetic macular edema, and retinal vein occlusion.
