Blurred vision. Blurred vision in one eye can be due to a myriad of causes and should be evaluated by an ophthalmologist as soon as possible. It would be considered an emergency if there is sudden loss of vison, pain, nausea or an injury. If unable to find an ophthalmology office open seek an emergency room for immediate care. Try not to rub the eye especially if there has been an injury and put a shield on it.
Numerous reasons. There are far too many possibilities that could cause blur in one eye to list here. The options would be narrowed by asking questions; was the blur sudden or gradual, are there any associated symptoms like pain, how severe is the blur etc. You should certainly see an eye doctor to determine whether this is the result of a health problem in your eye or you just need glasses.
Lots of reasons! Blurred vision in one eye could be simply a refractive error needing eyeglass correction or the result of disease affecting only that eye. The types of disease could be ocular surface, inflammatory disease, cataract, glaucoma, retinal disease, etc. Best to have this checked out by an eyemd as soon as possible.