my husband had this problem, usually towards the end of the day or as we were sitting down to eat. it affected both eyes, so he couldn't see anything. it is apparently quite common. two remedies were suggested. one was some special form of clip attached to his glasses - which was ruled out as unsuitable by the eye specialists - or botox.
he has been having three-monthly botox treatments at the hospital eye clinic for the past 18 months - the actual process takes about 10 minutes - and it has almost eliminated the problem. to my mind it is one of the most effective treatments he has had, for anything to do with his parkinson's.
there are downsides, of course. one is dry-eyes, and he has all sorts of drops, sprays and ointments for this. some people apparently do not tolerate the botox as well as he has, and it can affect the way your eyes look, as botox does. also, the effect starts to wear off by the end of 3 months and, at least here, there is only one clinic a month, so if you miss your slot for whatever reason, your eyes start shutting again before the next treatment. but so far, so good. to be recommended.