Understanding diplopia and recognising important warning signs

What diplopia means

Diplopia is the medical term for double vision. It occurs when you see two images of a single object instead of one. The images may appear side by side, one above the other, or at an angle. Diplopia can be temporary or persistent. Even when it settles on its own, it is taken seriously in healthcare because it reflects how the eyes and brain are working together.

How double vision presents

The way double vision appears often provides useful clues. Some people notice horizontal doubling, where images sit side by side. Others experience vertical doubling, with one image above the other, or diagonal doubling that combines both directions. Diplopia may also be accompanied by blurred vision, reduced depth perception, eye strain, or difficulty with tasks such as reading, walking, or driving.

Binocular and monocular diplopia

Diplopia is broadly classified into two types.
Binocular diplopia occurs only when both eyes are open and disappears when either eye is covered. This pattern usually reflects misalignment of the eyes, known as strabismus, or problems affecting the nerves or muscles that control eye movement.
Monocular diplopia persists in one eye even when the other eye is closed. This form is less common and is usually related to conditions within the eye itself, such as refractive error, cataract, or changes to the surface of the eye.

What can cause diplopia

Some episodes of double vision occur with fatigue, illness, or alcohol and resolve as those factors settle. In other cases, diplopia can signal underlying conditions that require assessment. These include problems affecting eye muscles, cranial nerves, or the nervous system, as well as metabolic conditions such as diabetes. Because causes range from minor to serious, context and associated symptoms matter when deciding next steps.

When medical review is important

A medical review is recommended when double vision is new, unexpected, persistent, or changing. Diplopia that appears suddenly, follows a head injury, or occurs alongside other symptoms such as headache, dizziness, weakness, speech difficulty, or swallowing problems requires prompt assessment. Your GP helps determine whether urgent care is needed and coordinates further evaluation if required.

How GPs approach assessment

Assessment usually starts with careful history-taking. Your GP asks about when the double vision began, whether it affects one or both eyes, how long it lasts, and what other symptoms are present. An examination of eye movements and general neurological function often follows. This structured approach helps identify patterns, decide whether investigations are needed, and guide safe referral when appropriate.

This article provides general health information only and does not replace medical advice. Please speak with your GP for personalised care.