Posterior Vitreous Detachment
Our eye is full of jelly called the vitreous humour which consists of 98% water and 2% collagen. As we age the protein component in the vitreous denaturises causing it to liquefy, with the result that instead of having the consistency of jelly, it is more like warm honey. Eventually the jelly becomes so liquefied that it collapses, pulling away from the retina. This process occurs in 20% of people at age 55 and up to 75% of people at age 65 and is termed a posterior vitreous detachment (PVD).
The initial symptoms of a PVD are similar to those of a retinal detachment:
- An increase in the number of visible floaters. These look like little mosquitoes or worms in your field of vision. They may move or be stationary but generally follow your line of sight.
- A flash of light (usually to one side) and which is like a camera flash. This is generally seen at night-time and can vary in frequency.
- A cobweb in your field of view. This is the thick outer edge of the vitreous and symptoms generally improve over a few months. Occasionally it can be secondary to a small vitreous haemorrhage that is caused by a bleed from a vessel damaged when the jelly tugs against the retina. The haemorrhage tends to dissolve over several weeks.
It is essential to perform a dilated fundus examination when you first develop symptoms of a PVD. This involves the optometrist placing drops in the eye to enlarge the pupil, waiting 20 minutes, then examining the retina to ensure no retinal breaks or tears have developed. Sometimes scleral indentation will be performed, which involves the optometrist pressing a small metal probe around the white part of the eye to facilitate a better view of the peripheral retina.
When symptoms of a PVD are first noticed, usually only a section of the jelly has started peeling off. This is termed a partial PVD, and is the reason a fundus examination needs to repeated 4 to 6 weeks after the initial symptoms. This is to detect if any retinal tears appear over the next month as the vitreous continues to detach from the retina. It would be prudent to avoid contact sports until the jelly has totally detached.
During the few months after the initial PVD, if symptoms become more frequent or you develop a shadow in your visual fields like a curtain or veil, you must return immediately for another retinal examination.
There is no treatment necessary for a PVD unless it is associated with a retinal break. The flashes of light will generally lessen after several weeks and the floaters after 6-9 months. If a large central floater develops then sometimes this can be treated with a YAG laser to break it into smaller floaters. Otherwise in visually debilitating cases a vitrectomy can be performed whereby the vitreous is surgically removed and replaced with clear fluid.
Sometimes an epi-retinal membrane can develop some months after a PVD. This is where a membrane similar in appearance to clear cellophane develops above the retinal surface. Very occasionally this membrane can affect the vision by wrinkling the retina, subsequently requiring surgical stripping.
Techniques to lessen the visual effect of a PVD:
- If a large centrally located floater is affecting your vision then roll your eye around to relocate it away from your visual axis.
- Wear your spectacles as clearer vision will make the floaters less apparent.
- Wear sunglasses. This will reduce the contrast of the shadow of the floater on your retina making it less obvious.
- Adjust your room illumination and the brightness of your computer screen.