POSTERIOR VITREOUS DETACHMENT. (PVD)

As people get older their eyes grow slightly, while the vitreous jelly inside breaks down, liquefies and shrinks. Eventually, this leads to the vitreous body being detached from the retina in 65% of 65 year olds and 100% of 90 year olds.  This process generally happens earlier in myopic, or short-sighted, people (as the myopic eye is already larger) and it leaves the jelly (which does not grow) under more tension. Vitreous jelly can also become dislodged during trauma.

 

SYMPTOMS
As the jelly pulls away from the retina it stimulates it. Unlike other parts of the body, the only sensation the retina can produce is sight and as it is stimulated the patient sees flashes of light - usually in their peripheral vision. The back of the vitreous is attached firmly to the optic nerve and as it pulls away it can bring away some of the fibres from around the nerve head. This is not nerve tissue, but the skin of the nerve, so the vision is not damaged by the process.  This change can often be seen by the ophthalmologist as a ring of tissue on the back of the jelly (known as a Weiss Ring) and may remain circular or can collapse into various shapes that cast a shadow on the retina, causing the patient to see a crescent moon, a spider or a cobweb shape or simply a  blob in their vision.

Diagram of a posterior vitreous detachment

 

The posterior vitreous detachment (PVD) is harmless. The flashing light it causes will usually stop completely and the floaters will be ignored by the brain in a similar way to which it ignores the blind spot, by filling in the background.  However, on bright sunny day and against a white background, the patient will still see these floaters when not preoccupied with other things.

Occasionally, as the vitreous detaches from the retina, it can pull on blood vessels causing bleeding or breaks in the retina that can lead to a retinal detachment.

 

 

TREATMENT

As there is always a risk that as the vitreous pulls on the retina, it can cause a retinal detachment, the patient should be warned about the symptoms that they can expect. These are the 3 F’s, Flashing lights, another shower of Floaters or a sudden Failing in vision, like a curtain coming in front of their vision. If they experience any of these they should seek an ophthalmic opinion as a matter of urgency.

There is an operation to remove the vitreous, a vitrectomy, that can be performed, but as there are risks to the procedure and very little benefit, it is not recommended except in exceptional circumstances. (i.e, when it effects your career, a fighter pilot may find that an unwanted floater hinder his abilities).

Click here to see an animated video of a vitrectomy (the surgical removal of the vitreous from the eye).