Hi there, we had a blind guinea girl, we had her for about 6 months before we found out - what are your guineas colours? Does he have red eyes? Often red eyed guineas can have weak to no eyesight and they manage perfectly well - but even the good sighted ones cannot see that well to be honest, and their sense of smell is the sense they rely on most, hence the scratching around - if your guinea has an established companion, the 'blind' one will rely very heavily on him/her, but in everything else will carry on as normal - what was he doing for you to think he was having a fit?? Hope all OK now.
If you hold your hand to his face does he move his head (not as is going to hit him or anything , just covering his eyes one at at time?) If he does have reduced vision, his sense of smell and hearing will serve him well. And he'll be more dependant on his brother.
Is he an Abbysynian? (Rossetted) They have more eyesight problems but IIRC that's cataracts (where the eyes would appear clouded and more opaque) .
My 2 Himalayan sows when I was a child had pink eyes. They didn't let it stop them but it did affect them. Like having to go round the side of a room until they knew it well enough to go across the floor.
Keep a check on him though. As you say, it might be something completely different. Do they tend to be competitive for food?
I cried loads when OB went blind in his left eye. But I think piggies have a diiferent view on life, well OB does. He was more Well that's odd, still onwards and upwards. OB did lose confidence for a couple of days. Didn't travel too far from his hutch. He moved like a ZuuZuu pet toy round the furniture whiskers touch change direction. Then he was back to his magnificent him. [Grin]