The vitreous humour is a clear, gel-like substance that fills the large space between the lens and the retina at the back of the eye. Comprising approximately 80% of the eye’s total volume, this component plays a significant role in maintaining the eye’s structural integrity and supporting clear vision. Understanding the vitreous humour provides insight into a fundamental part of eye health and how it contributes to sight.
What It’s Made Of and How It’s Structured
The vitreous humour is primarily composed of water, making up about 98-99% of its volume. The remaining small percentage consists mainly of collagen fibers, particularly Type II collagen, and hyaluronic acid. These components interweave to form a transparent, viscous gel, providing its structural integrity. While largely avascular, meaning it lacks blood vessels, the vitreous is enclosed by a collagen layer known as the vitreous membrane. It maintains various attachment points within the eye, including strong adhesion to the vitreous base (a band straddling the ora serrata), the optic nerve disc, and along major retinal blood vessels.
Its Roles in Vision
The vitreous humour performs several important functions that support clear vision and overall eye health, as its gel-like nature is instrumental in maintaining the spherical shape of the eyeball. This stable shape is important for light to focus correctly onto the retina. Beyond structural maintenance, the vitreous acts as a natural shock absorber, protecting the delicate retina from external forces or rapid movements. Its transparency is fundamental, allowing light to pass unimpeded from the lens to the retina. The vitreous also contributes to the eye’s metabolic balance by providing some limited nutrient support to surrounding avascular structures like the lens and parts of the retina, and by helping to maintain an oxygen gradient within the eye.
Age-Related Changes and Common Issues
The vitreous gel naturally undergoes changes with age, a process referred to as vitreous liquefaction or synchysis. This involves the collagen fibers clumping and the gel becoming more liquid, with over 50% potentially liquefying by age 80, a process that can begin as early as age four.
As the vitreous changes, small specks or strands, known as floaters, may appear in one’s field of vision. These floaters are caused by the aggregated collagen clumps casting shadows on the retina. While common and typically harmless, a sudden increase in their number can indicate a more serious underlying issue.
A more significant age-related change is Posterior Vitreous Detachment (PVD), which occurs when the liquefying vitreous pulls away from the retina. PVD is a common, natural part of aging, usually occurring after age 50, and is not painful or sight-threatening. Symptoms often include a sudden increase in floaters and flashes of light, especially in peripheral vision. While PVD itself is generally benign, it is important to seek prompt medical evaluation to rule out complications like retinal tears or detachment, which are medical emergencies requiring immediate attention.
Less common but more serious issues can also affect the vitreous, such as vitreous hemorrhage, which is bleeding into the vitreous. This can result from conditions like diabetic retinopathy, trauma, or retinal tears, and may cause sudden vision loss or blurred vision. Additionally, inflammatory conditions like vitritis, a form of uveitis, can lead to floaters, blurred vision, eye pain, and light sensitivity due to inflammation of the vitreous gel. Immediate medical attention is necessary for these conditions.