Another cause is being dominant with one eye.
You can force your brain to use your ignored eye, by wearing a patch over the dominate eye for an hour or even less, and things will become corrected. You'll notice the improvement straight away when you remove the patch, and if you eventually notice that one eye is becoming dominate again, you know how to correct things. A common cause of one eye becoming dominate, is frequent use of just one eye, such as watching the stars through a telescope every night, etc.
Also be aware that using an eye patch means that you'll lose your depth of perception/ability to judge distances, and of course half of your peripheral vision! So no driving, bicycling, or anything which requires much attention of your surroundings when wearing the patch, just stuff like eating dinner, watching tv, reading stuff on somersoft, etc