Many opticians are pretty experienced with a slit lamp (dunno if the plans to get them in on the screening of diabetic retinopathy etc. got carried through), but to be honest it'd need to be an ophthalmologist. Talk to your GP about it; it might well be that there's nothing to see on your retina, but it's always prudent to have a good look and make sure there's nothing to see.
I've got no idea why it's only in one eye. You can get similar symptoms from eye strain, though - when I was doing pathology as a student and spending hours a day staring down a microscope, I used to come out of the lab and notice that one eye was seeing much brighter than the other. Just one more reason to hate pathology....