Interesting. The nervous system, to turn a phrase, gets trashed during an orgasm. Some people see colors and "hear" colors, and "feel" sound etc. Some people can't walk, or their teeth chatter and they shake (me) some people have other minor and short lived neuro after effects of orgasm. A lot of people feel very sleepy and some feel energized (I couldn't fall asleep for well over 2 hours after a particularly spectacular set of Os last night, while my man happily conked off in about 4 seconds.)
Your blood pressure rises precipitously during an orgasm, also a lot of blood leaves your non essential organs (for the orgasms) like the eyes and sometimes extremities and GI system, and barrels towards the genitals. Sometimes it can take a few minutes for your nervous system and your circulatory system to work normally post orgasm.
Is it minor blurriness? This happens to some people when they lie down and is fairly normal? Or can you not see any features of things at all? You said it only lasts a few minutes some of the time, but hours others. Most post orgasmic events don't last a really long time (although the endorphin rush can sometimes last for a day or two after a particularly good session.) You may want to mention it to your GYN the next time you have a pelvic exam or the next time you have a Physical with your doctor.
I wouldn't worry too much, but if your body is telling you something is wrong, make an appointment so your mind will be at ease.
It's probably completely normal for you, but sometimes having an exam and making sure someone else OKs that it's normal is important.