Double vision can be either monocular or binocular. When it is monocular commonly it is related back to an uncorrected eyeglass or contact lens prescription need. Binocular double vision is always a misalignment of the two eyes.
Most binocular double vision occurs as a result of stress put upon a longstanding tendency for the eyes to misalign. That is certain people have eye postures that are more difficult for their neurological system to control. Once we add stress (reading and computer) the posturing between the two eyes breaks down. Fortunately these can be treated quite easily with eyeglasses and or vision therapy.
However, quite frankly acute onset of double vision can be startling to both doctor and patient alike. Many times it point to much more serious health concerns. Below is a table of the most common health conditions that can lead to the emergence of double vision.
Health and double vision:
Thyroid Disease: As Graves which causes a change in the tissue and the muscles of the eyes.
Diabetes: disrupts flow to the eye muscles
Hypertension: disrupts flow to the eye muscles
Stroke: Disrupts blood flow to the eye muscle control centers of the brain
Multiple Sclerosis: Directly changes the nerves in the central nervous system
Aneurysm: Disrupts blood flow or mechanically pushes on nerves or muscles
Brain Tumor: Pushes on the nerves or muscles
Myasthenia Gravis: weakens the muscles of the entire body including those that control the eyes.