You could have some loss of peripheral vision due to a disease such as glaucoma or other condition of the eye or nervous system or perhaps you just had difficulty with the test for unknown reasons (tired, nervous, eyes got dry etc.) It depends on the actual pattern seen on the results and number of false positives or false negatives and fixation losses. In other words are the results reliable. Unfortunately, I don't know but it is too early to start worrying. Take the test again and hopefully it will turn out normal. If abnormal then your ophthalmologist is going to have to figure out what is going on.
MJK MD
This may be totally wrong but its an idea, each eye sends a signal to your brain and sometime they are not of the same strength. if the eye that is closed is sending a stronger signal to your brain then your brain could be recieving a stronger signal of "darkness" than of the "world" from your open eye. Ive had the same test and it went in and out for me cause my right eye sends a stronger signal, this is caused because i should wear glasses but do not.