Courtesy of David Kinshuck © Good Hope Hospital
A clear jelly —the vitreous or ‘vitreous jelly’—fills the middle of the eye. The vitreous lies against the retina in the normal eye. It is transparent like glass, so light passes through it to reach the retina: the retina is the film that lines the back of the eye.
The Normal Eye
The eye is like a small ball, the size of a table-tennis ball.
Light enters the eye, and then passes through to fall on the retina. The retina turns the light into electrical signals, which are then sent to the brain.
As you get older the vitreous may shrink away from the retina. This may happen earlier if you are short sighted or have injured your eye. A PVD proably occurs in all of us.
This shrinking process may happen rather suddenly, that is over a few days. This process is called a posterior vitreous detachment.
The eye still sees well with a shrunken vitreous: the shrinkage is essentially like a jelly liquefying, and no harm comes to the eye.
The vitreous may shrink in different ways.
First, it may shrink away from the retina, and leave the retina unaffected. You may not notice if this happens.
Secondly, it may tug the retina gently. This may cause tiny flashes of light. These usually subside over a couple of weeks.
Third, you may develop floaters. Tiny amounts of pigment may come off the retina, into the vitreous, and this may cause floaters. You may see these as a spiders web or veil over the eye. The floaters disappear a little, and become less noticeable, over the next few weeks or months.
Floaters are naturally much more noticeable if you only have one good eye (and this process is happening in the good eye).
Less commonly, the vitreous may pull the retina and make a small retinal tear, or even less commonly, a detached retina.
When the vitreous shrinks it may cause blackish floaters and flashes of light.
Occasionally the PVD (the shrinking vitreous) pulls the retina to make a retinal tear.
Or a detached retina
If there is a vitreous haemorrhage, there is a nearly 2/3 chance there is a tear, and 1/3 chance there is a detachment. Risk of tear/detachment is slightly lower in if the patient is using anticoagulants.
If there is a haemorrhage there is a much higher risk of tear/detachment.
The Eye Examination
In the eye clinic or the eye emergency department your eye will be examined. So the doctor can see the edge of the retina to look for a retinal tear, your pupil will be dilated with drops. The drops take about 20 minutes to work, and your reading sight will be blurred for about two hours. (Very occasionally the sight is slightly blurred for a day or two.)
The examination may be carried out with several types of instrument, or even a contact lens, and occasionally the doctor has to press on the edge of the eye. This may be a little painful.
There is no treatment that will put the vitreous back in position. The floaters and veil that may have drifted across your sight subside by themselves. You may notice a large floater for a long time, which is a nuisance; the doctor can not remove this. As mentioned, most people become accustomed to the floater or floaters, and with a little effort ignore them.
Tears are uncommon, but if one develops, laser treatment around it, or freezing therapy, may be necessary to prevent the tear becoming larger.
If the doctor checks your eye and all is well, the floaters and flashes subside. However, you usually need a further examination if
- you suddenly develop a lot more flashes or floaters (this could be a small tear)
- a shutter or curtain of blurred vision drifts across your eye, sometimes from below. To check for this, cover one eye at a time for a few seconds every day. If the eye you have not covered sees well in all directions, all is well.
- 15% of people with a PVD and symptoms (flashes/floaters) do have a retinal tear. If the flashes do not settle after a few days and occur during the day a tear is more likely.
An area of poor sight drifting across your vision: if such a problem develops, you need a check the same day or next morning to determine whether or not there is a retinal detachment.
Test your sight everyday covering one eye at a time.