I am gathering that it happens when you are stressed more than other times? There are a few ways you can go get at the problem...
1- Go see your GP and ask about it. They'll do the little light in the eyes and either go HUMMM and say don't worry about it or they'll refer you to either a neurologist[studies the nerves] or an opthomologist [studies the eyes].
2-Or if you don't belong to an HMO [where you need a referral from the Primary doc [GP]], just go to the Opth...but, expect a longish wait for that first appointment....Once you are first seen, you are IN thereafter-if you know what I mean. An Opthomologist would likely give you a very good going over eye-wise, drops to dilate the pupils, all kinds of tests.
I will tell you I'd had [still occasionally had] a vision problem, one that came and went? And the problem was it rarely happened when I had a doc appt. What you might have is something that might have to be seen to be believed. In my case, I got very lucky as my problem occurred on the way to an opth appoinment - when the doc told me during that appointment he was about to 'write it all off as in my head' but for his actually seeing it. I then sure got tested for all things visual and then some as a result! Never did find the cause tho, but we both found out about what the problem wasn't!
MrsD has given you good advice and info to check out. Please listen to her.
Please let us know what happens, I hope you get the help you need! - j