Patients with proliferative diabetic retinopathy can be treated with laser photocoagulation and/or Avastin. Proliferative diabetic retinopathy, or PDR, is a specific stage of diabetic retinopathy which may lead to blindness if left untreated.
While most patients (if not all) develop some degree of diabetic retinopathy, most patients will not progress to the proliferative stage.
Diabetes is a disease which affects blood vessels. The retina may lose blood supply resulting in “retinal ischemia,” a condition where insufficient oxygen gets to the tissues (“angina” is another ischemic condition, chest pain develops due to lack of oxygen).
In response to chronic ischemia (poor oxygenation), the eye secretes VEGF (vascular endothelial growth factor). VEGF acts as a fertilizer to grow abnormal vessels somewhere in the eye. These abnormal vessels are called neovascularization.
Neovascular tissue may cause a diabetic retinal detachment or neovascular glaucoma. Either can blind.
Avastin, a common anti-VEGF, when used in the eye, can treat wet macular degeneration and macular edema. Over the last few years, Avastin has also been used to chemically treat PDR.
Avastin works by chemically neutralizing VEGF circulating in the eye.
Laser treatment, called pan-retinal photocoagulation (PRP), indirectly reduces VEGF by killing retinal cells. By reducing the number of retinal cells (we don’t really need them for vision by the way), the overall demand for oxygen is reduced. At some point, the reduced oxygen supply becomes adequate and VEGF is no longer produced.
Avastin, in my opinion and experience, is a quick and immediate treatment for PDR. It needs to be repeated as it does not fix the actual problem…the ischemia.
I have found that repeating the injections every 90 days or so can keep the neovascularization under control.
PRP, the laser photocoagulation, is a more permanent therapy as it remedies the actual problem…it cures the relative ischemia. Ischemia is inadequate supply of blood flow/oxygen. While the laser does not improve supply, it reduces demand and cures the oxygen problem.
What Does this Mean?
I don’t really know how long laser treatment takes to work on patients. There are several reasons why PRP is not immediately effective; severity of disease, amount of laser, etc.
Avastin works almost immediately and usually within 24-48 hours. It gives me a great clue as to the likely success of the eventual PRP.
I can often “stop” the disease with the Avastin and perform the more curative treatment at a later date.