Diplopia (double vision) is often the first manifestation of many systemic disorders, especially muscular or neurologic processes.
An accurate, clear description of the symptoms (eg, constant or intermittent; variable or unchanging; at near or at far; with one eye [monocular] or with both eyes [binocular]; horizontal, vertical, or oblique) is critical to appropriate diagnosis and management. Binocular diplopia (or true diplopia) is a breakdown in the fusional capacity of the binocular system. The normal neuromuscular coordination cannot maintain fusion of the visual objects on the retinas of the 2 eyes.
Double vision can in some cases be secondary to thyroid eye disease, myasthenia graves, tumors of the orbit or brain, or cerebral aneurysms, to name a few. More commonly, diplopia is a result of breakdown of the normal muscle function between the eyes, which is considered physiologic--as long as no other neurologic signs exist--and can be corrected with something called prism in most cases. Rarely, fusion cannot occur because of dissimilar image size, which can occur after changes in the optical function of the eye after a cataract is replaced by an intraocular lens.