There is a possibility of off gassing from too much lubricating oil, plastic components (if any), gasket sealants, ect. This, or moisture is the most probable cause. On one hand, a trip to a watchmaker for a service could fix that very easily. But if you want to fix it yourself, take the movement out of the case then just to be on the safe side put the open case and movement inside a container with some dry rice or silica gel packets. If moisture is the root problem that should remove the haze. If silica doesn't work then you issue is residue from off gassing material inside the watch. You should just be able to clean that off of the inside of the crystal with a soft cloth. If the problem persists then a full service or a replacement movement that's properly serviced is necessary.