Both macular degeneration and diabetic retinopathy can cause “blindness” from neovascularization. Both are diseases of the retina, both can lead to “blindness,” both increase with age/time and both can be associated with abnormal blood vessel formation known as “neovascularization.”
The two diseases differ in the location of the neovascularization.
Diabetic Retinopathy – In cases of diabetic retinopathy, the presence of neovascularization defines a particular stage of eye disease; proliferative diabetic retinopathy. The neovascularization may “proliferate” along the surface of the retina and other structures inside the eye. As long as the VEGF is circulating, the vessels will continue to grow.
Diabetic retinal detachments may occur if the the neovascular tissue proliferates out of control. Neovascular glaucoma may develop if the abnormal blood vessels “clog” the internal drain of the eye. In this case, intraocular fluid that normally filters out of the eye can no longer escape as the drain is closed. The pressure escalates out of control and severe pain (and redness) develop.
In short, proliferative diabetic retinopathy, as defined by the presence of neovascularization, can causes retinal detachments and neovascular glaucoma (not the usual form of glaucoma). Both are mechanisms by which diabetes can cause blindness.
Macular Degeneration – “Wet” macular degeneration, by definition, exists when neovascularization develops underneath the retina. This neovascular tissue causes physical separation of the layers of the retina and destruction of the normal tissue. Almost all neovascularization leaks, and, at times, bleeds. Loss of central vision occurs due to this rather rapid growth of abnormal blood vessels.
VEGF - In either case, neovascular tissue is a complex of “abnormal blood vessels.” As best we can tell, neovascular tissue develops in response to Vascular Endothelial Growth Factor, or VEGF. This growth factor causes both proliferation of the neovascular tissue and sustains existing neovascularization. Without circulating VEGF, the neovascular tissue shrinks up and goes away.
Anti-VEGF treatments are simply directed at blocking the effects of VEGF.
Anti-VEGF medications (e.g. Avastin, Lucentis and Macugen) are antibody like molecules that find circulating VEGF and prevent VEGF from “doing its duty.” The treatment of choice for proliferative diabetic retinopathy remains pan-retinal photocoagulation (PRP). The end result of PRP is decreased … VEGF.
With timely diagnosis, both diseases can usually be controlled. Neovascularization in diabetes can be reversed before a retinal detachment is formed, neovascular glaucoma may be reversed and “wet” macular degeneration can be halted.
What Does This Mean? A few years ago, I would not have been able to write this article. We have learned a lot about the mechanisms by which both diabetic retinopathy and macular degeneration cause blindness. It amazes me how the pathogenesis (i.e. the disease process) of both diseases are so similar. Both diseases can cause blindness via VEGF.
This is why it is so confusing. Two separate diseases that respond to the same treatment.