Does the vitreous grow back after vitrectomy surgery?

What is the vitreous, and why do we have it?

The vitreous is the transparent gel behind the lens and in front of the retina. It is about 99% water. A delicate network of collagen fibres and hyaluronan, a molecule that holds water, gives it its jelly-like consistency. It also contains small amounts of salts, proteins and cells.

It has an important role while the eye develops. Before birth, temporary blood vessels run through the developing vitreous and supply the forming eye, including the lens. These vessels normally disappear as development progresses. The gel also provides a clear, supportive environment within the growing eye.

By adulthood, the eye can retain its shape and work without this gel. That does not mean the vitreous has no remaining functions: one is helping regulate oxygen inside the eye.

What are the benefits of removing the vitreous?

Removing troublesome vitreous can improve vision in two main ways:

• A clearer path for light. Removing gel containing dense floaters or blood can improve visual clarity. The benefit depends on the health of the retina and the rest of the eye.
• Relief from pulling on the retina. Vitreous traction can contribute to retinal tears and macular holes. Releasing that traction is an important part of vitrectomy surgery for these conditions.

The removed gel can no longer tug on the retina. However, this does not mean vitrectomy guarantees protection from retinal detachment. Some vitreous usually remains at the edges of the eye, and retinal tears or detachment can occur during or after surgery. Vitrectomy is used to treat a problem, rather than routinely removing healthy gel to prevent one.

What replaces the gel during surgery?

As the gel is removed, the surgeon continuously replaces it with a sterile balanced salt solution. This is a physiological irrigation fluid designed for use inside the eye. Its salt concentration and pH are carefully controlled to suit delicate eye tissues.

Solutions such as BSS contain sodium, potassium, calcium and magnesium salts, with acetate and citrate to help maintain the chemical balance. BSS Plus also contains bicarbonate and phosphate buffers, glucose and glutathione, an antioxidant-related substance. Its pH is approximately 7.4, close to the body’s normal physiological pH, and its concentration of dissolved particles is close to that of natural eye fluid.

These solutions are prepared specifically for eye surgery, rather than being plain water. Depending on the retinal problem, the surgeon may instead leave an air or gas bubble, or silicone oil, at the end of the operation. Those have a separate role in supporting retinal repair.

What replaces the surgical fluid afterwards?

The eye continues making its own clear fluid, called aqueous humour. It is produced by the ciliary body, a ring of tissue behind the iris. After vitrectomy, this natural fluid gradually replaces the balanced salt solution in the space previously occupied by the gel.

Replacement is a continuous process over the days after surgery, rather than a single changeover at a set time. There is no precisely established replacement time that applies to every eye. Normal aqueous production is only a few thousandths of a millilitre per minute and varies through the day. This fluid turnover should not be confused with the time needed for vision to recover.

A gas bubble takes longer to disappear, depending on the gas used. Silicone oil does not gradually turn into natural fluid; it usually needs a further operation to remove it.

What keeps the eye inflated without the gel?

The eye stays filled with fluid. Its tough outer wall, the sclera, together with controlled internal fluid pressure, helps maintain its shape. During surgery, the irrigation system maintains the fill and pressure. Afterwards, the balance between natural fluid production and drainage maintains eye pressure. The eye does not need the vitreous gel to act as a permanent internal prop.

Why can vitrectomy cause cataracts?

The vitreous gel and its antioxidants help limit the amount of oxygen reaching the natural lens. Removing the gel changes oxygen movement inside the eye and can speed up clouding of the lens. This is why cataracts commonly progress after vitrectomy in an eye that still has its natural lens.

The separate article Why does vitrectomy cause cataracts? explains this in more detail. An artificial lens implant cannot develop this type of cataract.