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Dave,
Macular puckering can be caused by several things including a hole in the retina. It could also be related to your previous holes and treatment (especially cryo). Whenever macular pucker is seen, it is important to make sure a hole is not present. Sometimes a small hole can be difficult to find. For this reason, your ophthalmologist is probably recommending a conservative apporach. One option may be to have your eyes reexamined a few days before the marathon to recheck for holes.
Since I have not examined you, I cannot advise you about the risks of running the marathon. This is best discussed with your physician.
This information is for educational purposes only. Please consult your physician for diagnostic and treatment options.
Sincerely,
HFHS MD - NI