Can plavix (clopidogrel) cause vision loss? My father (75 years old) had a stroke 10 months ago. He has also glaucoma and the cataract is starting.

Not likely. Of all his medical conditions, the stroke, the cataract and the glaucoma are all much more likely to be the source of his vision loss. Ask his eye md which his primary problem is.
Generally no. There have been some cases of retinal hemorrhage related to Plavix (clopidogrel) use, but overall the cardiovascular benefits greatly outweigh the risks. Glaucoma, cataract, and vascular disease can all cause vision loss, however.