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by Philip Filner, Ph. D.
Symposium
An international symposium, entitled
"Radiation Therapy for Macular Degeneration", was held on March 21, 1997, in New York City. Results were reported from the leading centers at which radiation therapy is
being tried as a treatment for arresting leakage and deterioration of central vision caused by subfoveal or non-classical neovascularizations in cases of wet form macular
degeneration. These are cases for which laser surgery is not appropiate.
Subfoveal neovascularizations are not treated by laser surgery because the laser beam will damage the
overlying fovea, and thereby cause a large, immediate, permanent deterioration of vision. Non-classical neovascularizations are those which do not have well-defined edges, so they do
not offer a clear target for laser surgery.
PF attended the symposium as representative of the Macular Degeneration Foundation.
The most important presentations were
those of Dr.David R. Guyer, and Dr.Richard F. Spaide, of the Manhattan Eye, Ear & Throat Hospital. Dr. Guyer reported results from the first large-scale control group of patients,
and a comparison of that group with a group treated with Interferon alpha-21, which, in a preliminary small-scale study appeared to have potential as a drug for treating wet form
macular degeneration.The large-scale study showed that Interferon alpha-21 did not help, and at high levels damaged vision. Dr. Spaide reported results from a group of patients
treated with radiation. and compared with the same control group described by Dr. Guyer.
After 1 year, 38% (confidence limits 29%-48%) of the control group of 105 exhibited a
decline of at least 3 lines of visual acuity. 91 patients meeting the same criteria as the patients in the control group were treated with 10 Gray (about equal to 1,000 REM).
This radiation dose is at the low end of the mid-range of radiation doses used in other studies, mostly with smaller numbers of treated patients, and either no control group or
inadequately small control groups. These inadequately controlled studies generally found 50 - 75% of treated patients exhibited stable or improved vision after 1 year. Doses in the
range 12 - 20 Gray have been used in most studies. Higher doses probably have been avoided because they approach the level at which radiation can damage the retina. Avoidance of
irradiation of the lens is essential because the doses being tried on neovascularizations are more than enough to to cause formation of radiation-induced cataracts.
Dr. Spaide
reported that after 1 year, 48.2% of treated patients lost 3 or more lines of visual acuity. The difference in values of 48.2% for treated patients and 38.1% for control patients did
not reach statistical significance. His bottom line:
"These results suggest that patients should not be treated with this dose of external beam radiation for CNV
(=Choroid NeoVascularization) secondary to AMD (=Age Related Macular Degeneration)."
Dr. Guyer also reported noteworthy observations concerning the individual natural
histories of the progression of macular degeneration in some control patients. There were a few instances of spontaneous improvements, including cessation or large reduction in
leakage, and improvement in visual acuity.
Thus, 62% of control patients experienced less than a 3 line decline in visual acuity after 1 year, and a few patients actually
exhibited substantial reductions in leakage from neovascularizations and improvement in visual acuity. These results from the first well-controlled study raise a very large doubt
about the signifcance of the reports of 50% - 75% of radiation-treated patients having stable or improved vision after 1 year, in studies with poor or no controls.
Posted May 23, 1997 |
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