Double vision - Causes and Symptoms

Definition

Double vision (or diplopia ) is a visual symptom that is manifested by the simultaneous perception of two images related to a single object. It can be caused by various conditions: some are relatively minor, others require urgent medical treatment.

Double vision can be monocular or binocular, transient, constant or intermittent.

The monocular diplopia occurs in only one eye (the other eye perceives images of normal quality for brightness, contrast and sharpness). When the part manifesting the symptom is covered, the double vision usually disappears and the subject should be able to see normally. Monocular diplopia can occur when something distorts the transmission of visual information, as happens in the case of scars or other irregularities on the surface of the cornea. The most common causes include keratoconus (deformation of the cornea, which becomes progressively thin and conical in shape), cataract (opacity of the lens) and incorrect refraction defects (usually astigmatism).

Instead, binocular diplopia occurs when both eyes cannot converge to focus on the same object. Often, it represents the result of an ocular misalignment, as typically happens in strabismus: the slightly deviated visual axes, cause the sending of different visual information. The result is the perception of two distinct images of equal quality. The binocular diplopia disappears when one of the two eyes is covered. Most of the time, the eyes are misaligned due to a disorder affecting the extrinsic muscles or cranial nerves that innervate them. Therefore, binocular diplopia can be the result of traumas of the eye or cranial orbit, inflammatory or infectious lesions. An endocrine-related exophthalm (especially in the case of thyroid hyperactivity) or the presence of tumors (at the base of the skull, in the area of the breasts or orbit) can also mechanically interfere with eye movement and determine diplopia.

Diseases that affect the blood vessels supplying blood to the eye or brain structures can cause sudden double-onset vision (eg, aneurysm, stroke, or transient ischemic attack). Other causes involve disorders of neuromuscular transmission, such as botulism, multiple sclerosis and myasthenia gravis. Paralysis of the cranial nerves (III, IV, VI) and retinal abnormalities, such as detachment or macular degeneration, can also cause double vision.

Temporary diplopia, on the other hand, may suggest a traumatic event (eg concussion), excessive physical tiredness or intoxication from a substance (such as alcohol or some drugs).