What Causes Swelling Behind The Eyes?

Have swelling behind the right eye..at times it is painful and my sight is fuzzy with my seeing black spots at times as well as a string like thing in the eye, but there actually isn t. An MRI showed immense and angry swelling behind the eye. There has been no evidence of infection or drainage. When I looked the MRI it appeared like a large angry volcano. And of course, this eye is sensitive to strong light.....the right eye doesn t appear to affected as I m able to see well out of if, but now am noticing some haziness in it, which is most likely a cataract forming. This eye, I know to get checked for the cataract & take whatever steps to consult about cararact surgery at some point....but the left eye is concerning me....what could possible be causing such swelling in the back of it?