How does the vitreous change with age?

What is the vitreous?

The vitreous is the clear gel that fills the space between the lens and the retina, the light-sensitive lining at the back of the eye. A fine network of collagen fibres holds water within the gel. In a young eye, this network gives the vitreous a relatively firm, gel-like consistency.

The same fibres are discussed in What are eye floaters made of?

Further explanation: Why does myopia increase the risk of retinal detachment and myopic macular degeneration?.

How is it like an egg?

An analogy I use is to compare the changing consistency of the vitreous with an egg:

• When we are young: the gel is thicker and holds together, rather like a semi-boiled egg.
• As we get older: it becomes softer and more runny, like a soft-boiled egg.
• With further ageing: a larger proportion is liquid, more like a raw egg.

How does this lead to a PVD?

As the collagen network changes, pockets of liquid form and some fibres gather into clumps. The remaining gel loses its firm structure and contracts. At the same time, the attachment between the gel and the retina becomes weaker.

Together, these changes allow the back surface of the gel to separate from the retina. Liquid fills the space behind it. The gel usually remains attached near the front edge of the retina, so a PVD does not mean that the gel has seperated from the entire retina.

Clumped fibres can cast shadows on the retina, as explained in How do floaters cause symptoms?

Can the separating gel tear the retina?

Sometimes the gel is still firmly attached at a particular spot. As it moves away, it can tug on that spot. This pulling is called traction, and occasionally it creates a retinal tear.

If liquid passes through a tear and collects beneath the retina, it can lift the retina away from the eye wall, causing a retinal detachment. A PVD is therefore different from a retinal detachment: one is separation of the gel; the other is separation of the retina itself.

Most PVDs occur without a retinal tear. The Floaters guide explains what an examination checks and how uncomplicated PVD is usually managed.

When should I seek urgent advice?

Arrange an urgent dilated retinal examination today if you notice:

• New flashes or a sudden increase or shower of floaters.
• A new shadow, curtain or missing area of vision.
• New blurred or reduced vision.

Contact your ophthalmologist urgently, or attend an emergency department. Read Flashes, floaters or a curtain: when is it urgent? for more detail.