What is the reason my ischemic crvo is helped with glasses. when i was told they would not help for this condition.

CRVO is a disease : Of the retina circulation. You are lucky you still have correctable vision in that eye. You did have a prescription for glasses before and they appear to be working. The glasses do not fix the crvo problem.

Refractive error: Most cases of ischemic crvo lead to profound visual loss. I hope you are receiving care as there are both short ; long term risks with these. Rx-glasses really just correct a possible co-existing refractive error. They have "therapeutic" effects on crvo. Be sure to discuss this with your eye physician.