3 year old w/PDD-NOS has rapid eye blinking

I was wondering if anyone has ever seen this before.  My son will be 3 on Wednesday and about 3 weeks ago he started rapidly blinking his eyes. I was doing a workshop for behaviors for kids on the Autism Spectrum and they had mentioned that you should make sure that there is not a medical reason for self stimulitory behaviors. I started to think that maybe he was having a problem with his vison which is why he started doing this so I had asked about the eye blinking. Someone mentioned that her son does the same thing but his eye blinking was siezure activity. I didn't think much into that because he does this so many times a day. Last week his therapist was here for an hour and he did did it at least half the time she was here.

We have tried to find a pattern or triggers but it seems to happen in just about any situation. He could be happy, sad, mad, whatever. He could be looking at a book, playing with playdoh, watching Tv andything. There is no difference between mood or environment when he does it.

He also doesn't seem aware that it is happening and it only last for a few seconds. He is on the sprectrum and also a a pretty significant speech delay so it's hard to tell because there have been times when he is hurt and can't tell us. His communication isn't always the greatest. We are just going by how well we know him and it doesn't look like he even realizes he is doing this. after a few seconds of the eye blinking he just keeps on doing whatever it is that he was doing in the first place.

We have noticed him doing this probably about once a month or once every two months before it became this often. We have always just chocked it up to one of those little quirky things he does. But now we are a little concerned.

Unfortunately both sides of the family have a history of siezures. My son has 2 uncles and 2 cousins that have siezures. 2 of them were when they were inafnts (less than 8 months old). Does anyone have any ideas, other than absence siezures, what this can be?