In proliferative diabetic retinopathy (PDR), abnormal blood
vessels and scar tissue grow on the surface of the retina and
also attach firmly to the back surface of the vitreous. The
vitreous then pulls on the scar tissue and can cause the blood
vessels to bleed into the vitreous cavity (called vitreous
hemorrhage). This can cause immediate and severe visual loss.
Often, the hemorrhage will clear by itself. If it doesn't clear,
a vitrectomy can be performed to remove the blood-filled vitreous.
When the vitreous pulls on the scar tissue, it can detach the
retina. This is called a "traction retinal detachment". When the
detachment involves the macula, central vision is lost. Also,
scar tissue may wrinkle the retina and cause visual loss.
The patient can regain some vision only if the scar tissue is
removed from the surface of the retina and the retina is
reattached. This is accomplished by vitrectomy. The surgeon
removes the vitreous and scar tissue from the surface of the
retina so that they stop pulling on the retina, thereby releasing
the traction. Removal of the scar tissue also reduces or
eliminates wrinkling of the retina.
The surgeon may use laser inside the eye to prevent later
development of abnormal new blood vessels on the iris, called
"rubeosis". Preventing rubeosis is important since rubeosis may
casue bleeding and blinding glaucoma. Laser is used to seal off
any tears of the retina. If there are tears of the retina, a
large air bubble may be placed in the eye to press the retina
completely against the back wall of the eye while the laser
treatment takes hold. In time, the air bubble will disappear and
be replaced by the eye's own fluid.