Yes, old contact lenses may cause eye floaters. Generally speaking, floaters are basically little blobs of protein that float through the hollow sphere which is filled with a thick, gel like fluid. According to some researches, when your eyes are infected by some virus, it can easy to have floaters. And if you wear the old contact lenses which are full with virus. So it can just make your eyes infected easily. At this moment, you should take off your old contact lenses, and then have some eye drops.
Yes, wearing the old contact lenses will cause floaters because of the dryness. As we know, the dryness can be the main reason to cause the eye floaters. Those people who have to sit in front of the computers for a long time will easily get the floaters. If you wear the old contact lenses, you will easily get the bacterium in the eyes and get the dryness. You'd better use some eye drops to release the symptom. You'd better not wear the old contact lenses any more which will be so bad for your eyes. You could also use some warm compress to make your eyes feel comfortable.
The symptom of eyes floaters are representing the black dots which float follows the movements of your eyes, just like flying mosquito. The shape of the dots may be circle, oval, spot or threadiness. The vision will be effect by this symptom in certain extends. It may be caused by eye inflammation or intraocular hemorrhage. It may affect the retina and become worse. If you wearing the old contact lenses which beyond the quality guarantee periods, the exceed standard of levels of virus will cause the red eyes or inflammation of your eyes. The inflammation may cause the floaters but I suggest that you go to doctor to check the detailed situation for sure.