IANAD/N, but I do work in an ophthalmology department at a hospital. Whenever eye twitches have come up as a topic of conversation at work, the universal reply has been “stress.” I suspect there are other causes, but that’s pretty much the primary cause.
I get these occasionally. In my case, they’re uncorrelated with stress, but instead are related to lack of sleep (although not necessarily actual sleepiness), which probably produces similar physical effects as stress. Interestingly, the twitches tend to hang around for a day or two even after I pay off the sleep debt.
I’ve also had eye twitches recently, associated with lack of sleep. I’ve found that eye drops help a lot (just artificial tears, not Visine or anything like that). I assumed it might be because of all the computer work (and sometimes games) and not blinking enough.