My husband Alan has the same problem
He wears glasses to read and write but when he takes them off he said it's like looking at 2 pictures that are slightly out of enlignment (only just) which makes it hard for him to focus properly, he found that if he uses light magnification lenses he can see quite clearly, but to read things he has to go back to his standard glasses which are 2.5 mag.
He is going to get his eyes checked as soon as he can because he is getting sick of carrying glasses around with him all the time... He was also told by an old mate of his (he doesn't wear glasses) that eye exercises are very important as the eye muscles loose there strength thru old age
Alan
These are not normal symptoms and I would start with a complete exam with a ophthalmologist to look for any obvious abnormalities. The only good news is that it is only intermittant but still I recommend a complete exam for starters to see what is going on. There are several different possible causes so I don't want to get into any more details until after that initial workup.
Michael Kutryb, MD
Kutryb EYe Institute
Titusville, FL
321-267-2020
www.kutrybeye.com