Could it have first happened as a reaction to something physical, ie. touching something then touching his eyes, but now he remembers it and gets worked up with the memory and association?
And as for opticians, I have lost some faith in them, esp. after reading about mystery shopper report on them in Reader's Digest recently. I really would insist that GP refer's him to local hospital for an opinion, if he continues to be bothered with it. Perhaps find out if there is a clinic such as 10-12(am) as with a hospital near me. GP refers you there, normally with a referral letter to bring, if you present your little one at the surgery of a morning with what the GP subsequently feels is an urgent problem, ie. something that has materialised overnight or needs to be seen urgently.
In any case, I wouldn't take no for an answer from any medical professional, if you feel there's something more to it, after all you know him best and we only get one pair of eyes.
In my experience, (when eldest did a Houdini out of 5-point car seat straps to nab pencil out of pencil case in change bag, purposely on far side of the car and poked her eye with it), I hauled ourselves up to A&E, me 8 months pregnant and in the rain, on a traditionally busy Friday night, just to be on the safe side and we were in the hospital for no longer than 30-45 mins? Just about to sit after booking in when we were called in and seen straight away, so they do take eyes very seriously indeed.
Anyway, hope he's sleeping soundly at the moment, like my two little creatures!
Keep us posted.
Minz