What Causes Jelly Like Substance In Eyes?

I have a clear, stringy jelly like substance that appears in both eyes, floating on my eye ball and obstructs my vision when it crosses my pupil. i can locate it in a mirror and with great difficulty have even been able 2 remove it from my eye once or twice. the doctors can't suggest what it is and haven't been able to help me. i have been suffering with this for over 6 months.