The majority of the eyeball’s volume is occupied by a clear, gelatinous material. This substance maintains the eye’s physical structure and ensures light travels correctly to the retina. Understanding the nature of this internal gel is helpful for recognizing common, age-related changes in vision.
Identifying the Vitreous Humor
The jelly-like material that fills the largest portion of the eye is called the vitreous humor, or vitreous body. This clear, colorless gel occupies the space between the lens at the front and the retina lining the back of the eye, making up approximately 80% of the eyeball’s total volume.
The vitreous humor is nearly 99% water, held in a semi-solid state by a delicate scaffolding of fine collagen fibers and hyaluronic acid. Hyaluronic acid allows the substance to retain water, creating its distinct viscous consistency.
The vitreous humor contains very few cells, mainly specialized phagocytes and hyalocytes. Phagocytes help remove cellular debris, keeping the visual field clear. The gel is formed primarily during embryonic development and does not undergo continuous secretion and drainage.
Essential Functions in Vision
The vitreous humor supports the visual system. Its primary purpose is structural support, helping the eyeball maintain its spherical shape and the internal pressure necessary for proper light focusing.
The gel also exerts steady pressure that keeps the delicate retinal layer pressed against the back wall of the eye. This support prevents the retina from detaching from the underlying vascular layer. Additionally, the vitreous acts as a soft, viscous shock absorber, protecting internal structures, particularly the retina, from physical trauma.
The transparent nature of the vitreous humor is necessary for clear vision. Since light must travel unimpeded from the lens to the retina, the gel’s clarity ensures visual stimuli reach the light-sensitive cells without distortion. It also transports oxygen and nutrients, assisting in the nourishment of surrounding tissues.
Why We See Floaters and Flashes
The most common changes occur when the vitreous humor ages and begins to liquefy, a natural process known as vitreous syneresis. This liquefaction causes the collagen fibers within the gel to clump together, forming small pieces of debris.
These clumps are known as floaters, appearing as specks, threads, or cobweb shapes drifting across the field of vision. Floaters are shadows cast upon the retina by the condensed fibers floating in the liquefied vitreous. They are often more noticeable when looking at a bright, plain surface, such as a blue sky or a white wall.
Eventually, the shrinking vitreous gel may pull away from the retina, a condition called Posterior Vitreous Detachment (PVD). When the vitreous tugs on the retina during this separation, it mechanically stimulates the light-sensitive cells. This stimulation is perceived as brief flashes of light, known as photopsias, typically seen in the peripheral vision.
Although PVD is a normal, age-related change that often occurs in patients over 65, a sudden increase in floaters or flashes requires an urgent eye examination. These symptoms can indicate a more serious issue, such as a retinal tear or detachment, which requires prompt medical attention.
How the Vitreous Differs from Aqueous Humor
It is helpful to distinguish the vitreous humor from the aqueous humor. The vitreous humor is the thick, gel-like substance that fills the large posterior segment (the back of the eye). Unlike the aqueous humor, the vitreous is largely static and does not undergo a regular formation and drainage process.
In contrast, the aqueous humor is a thin, watery fluid that fills the smaller anterior segment, located between the cornea and the lens. The aqueous humor is continuously produced by the ciliary body and constantly drained through the trabecular meshwork. This constant renewal helps maintain intraocular pressure and provides nourishment to the surrounding tissues.