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Diplopia is the medical term for the condition known as double vision. In this condition, a person perceives two separate images when looking at a single object. The answer to the question, “What is diplopia?” is that it is not a disease in itself, but typically a symptom of another underlying health problem. Therefore, it is crucial that individuals experiencing double vision take this condition seriously. Double vision can make daily activities such as reading and driving difficult, lead to balance problems, and significantly reduce quality of life.
The causes of double vision range from simple reasons like eye strain to ocular problems such as cataracts or strabismus, or even serious conditions related to the brain, like cerebral aneurysms, tumors, or neurological disorders. For this reason, if a symptom of double vision is noticed—especially if it begins suddenly or is accompanied by other symptoms—it can be vitally important to consult an ophthalmologist or a neurologist without delay. Although double vision can occur at any age, it is more common in individuals over 60. This fact demonstrates how closely eye health is linked to overall body health; systemic conditions such as diabetes, hypertension, or thyroid diseases can also lead to double vision. Consequently, a complaint of double vision should be evaluated not just as an eye problem, but as a potential sign of a broader health issue.
Table of Contents
How Does Double Vision Occur?
Normally, for healthy vision, both of our eyes work together in harmony. When we look at an object, both eyes focus on the same point and transmit images of this object from slightly different angles to the brain. The brain then fuses these two images into a single, clear, and three-dimensional picture. This complex process requires the perfect coordination of the eye muscles and the nerves that control them.
So, how does double vision occur? Diplopia arises when this delicate mechanism is disrupted. This disruption can happen through two main mechanisms:
- Eye Misalignment Problems (Binocular Diplopia): This is the most common situation. Due to a weakness, paralysis, or restriction in the eye muscles, or damage to the nerves that control them, the eyes become unable to look at the same point. In this case, each eye captures a different image, and the brain cannot fuse these very different images into a single one. As a result, the person sees double when both eyes are open. This condition is also known as strabismus.
- Intraocular Optical Problems (Monocular Diplopia): In this rarer situation, the problem is not with the alignment of the eyes but within the optical structures of a single eye. Irregularities on the cornea (e.g., astigmatism, keratoconus), opacities in the lens (cataract), or other structural defects can cause light to scatter or be refracted incorrectly within the eye, creating a perception of multiple or a ghosted double image even when looking with only one eye.
The brain’s reaction to this situation can vary with age. In cases of strabismus that develop in childhood, the brain may suppress the image from the misaligned eye to prevent double vision. Although this prevents diplopia, it leads to the failure of the suppressed eye’s visual ability to develop, resulting in amblyopia (lazy eye). In adults, the brain has generally lost this ability to suppress, so the complaint of double vision is more pronounced and bothersome in strabismus that develops later in life.
Types of Diplopia
To understand the cause of double vision, it is important to classify the diplopia. This classification helps to determine the source of the problem (the eye itself or the mechanism of the eyes working together). The most fundamental distinction is based on whether the double vision occurs in one eye or only when both eyes are open.
Binocular Diplopia
Binocular diplopia is a condition where double vision is experienced only when both eyes are open. When the person closes either eye, the double vision instantly disappears, and they begin to see a single image. This condition is caused by the eyes not being aligned, i.e., from strabismus. The causes of binocular double vision include weakness, paralysis (this is the answer to “what is diplopia and paralytic strabismus?”), over-contraction, or imbalances in the movements of the eye muscles. Additionally, damage to the nerves that control these muscles (cranial nerve palsies) can also lead to binocular diplopia. Binocular diplopia can often be a sign of an underlying neurological or systemic disease.
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Monocular Diplopia (Double Vision in One Eye)
Monocular diplopia is a condition where the double vision persists even when looking with a single eye, as long as the affected eye is not covered. It is rarer than binocular diplopia. The answer to “What causes double vision in one eye?” is usually structural problems within the eye itself. Conditions that prevent light from focusing properly as it enters or travels through the eye are among the causes of monocular diplopia. The most common causes of monocular diplopia are:
- Astigmatism: The inability of light to focus on a single point due to the irregular shape of the cornea or lens.
- Cataract: The clouding of the ocular lens, which can cause light to scatter and form multiple images.
- Corneal Problems: Keratoconus (conical cornea), corneal scars, post-infection scarring, or surface irregularities.
- Dry Eye Disease: An irregular tear film on the ocular surface can affect light refraction, causing temporary or ghosted double vision.
- Lens Problems: Conditions such as dislocation of the lens (subluxation).
- Retinal Problems: Retinal diseases like macular edema or an epiretinal membrane can also rarely cause monocular diplopia.
Monocular diplopia is often described as a ghost image, meaning a fainter, secondary image is perceived next to the primary one.
| Feature | Monocular Diplopia | Binocular Diplopia |
|---|---|---|
| Definition | Double vision in one eye | Double vision when both eyes are open |
| Eye Closure Test | Continues when the affected eye is open | Resolves when one eye is closed |
| Common Causes | Structural problems within the eye (Cataract, Astigmatism, Corneal Issues, Dry Eye) | Eye alignment problems (Strabismus, Muscle/Nerve Paralysis, Systemic Diseases, Neurological Issues) |
Horizontal Diplopia
Horizontal diplopia is a type of double vision where the two images are seen side-by-side. It typically occurs when there is a problem with the muscles that control the inward or outward movement of the eyes (medial or lateral rectus muscles) or the nerves that innervate them (especially the 6th cranial nerve).
Vertical Diplopia
Vertical diplopia is a condition where the images are perceived one on top of the other. This condition is generally seen when there is a problem with the muscles responsible for the upward or downward movements of the eyes (superior or inferior rectus/oblique muscles) or the related nerves (3rd or 4th cranial nerves).
Other Concepts:
- Physiological Diplopia: This is a normal, non-pathological visual phenomenon. It is the slight double vision of objects in the background when we focus on a near object, or of objects in the foreground when we focus on the distance. Our brain usually prevents us from noticing or suppresses this double vision.
- Diplopia on Focusing: This is double vision that appears or worsens specifically when focusing on near tasks (e.g., seeing text double). This can be caused by an insufficiency in the inward turning movement of the eyes (convergence insufficiency) or problems with the eye’s focusing mechanism (accommodation). Eye strain can also trigger this type of double vision.
Causes of Double Vision at a Distance
While double vision can occur at any distance, some conditions become more pronounced or are only noticed when looking into the distance. The causes of double vision at a distance include problems related to the eye muscles and nerves, as well as some systemic and neurological diseases.
General Causes Affecting Distance Vision:
- Eye Muscle Problems: An imbalance, weakness, or paralysis in the eye muscles can disrupt the precise alignment required to focus at a distance. Problems with the muscles that control outward gaze or a weakness in the ability of the eyes to move apart (divergence insufficiency) can cause distance diplopia.
- Nerve Problems: Palsies of the cranial nerves that control eye muscles (especially the 6th nerve, which controls outward gaze) can lead to double vision at a distance.
Specific Conditions That Can Cause Distance Diplopia:
- Strabismus: In some types of eye misalignment, the deviation is more apparent when looking into the distance.
- Neurological Diseases: Conditions like Multiple Sclerosis (MS), Myasthenia Gravis, stroke, brain tumors, and increased intracranial pressure can affect the nerves controlling eye movements, causing double vision.
- Cataract: Although it typically causes monocular diplopia, the blurriness and light scattering it creates can degrade overall visual quality and affect distance vision.
- Hypertension-related double vision: High blood pressure can damage the small vessels that supply the ocular nerves, leading to temporary nerve palsies and subsequent double vision.
- Eye strain-related double vision: Prolonged visual effort, especially with uncorrected refractive errors, can fatigue the eye muscles and cause temporary double vision.
- Dry eye-related double vision: Dryness on the ocular surface can degrade visual quality, especially during distance viewing in windy or air-conditioned environments, leading to a sensation of wavy or ghosted double vision.
- Amblyopia and diplopia: Amblyopia (lazy eye) is usually associated with the brain suppressing one eye to prevent double vision. However, if the underlying cause (e.g., strabismus) persists or is treated (especially at an older age), double vision may appear or become noticeable.
- Thyroid Eye Disease (Graves’ Ophthalmopathy): In this condition associated with an overactive thyroid gland, the eye muscles and surrounding tissues swell and stiffen. This restricts eye movements, causing binocular double vision, especially in certain directions of gaze (including distance).
- Trauma: Head or eye injuries can damage nerves or muscles, leading to permanent or temporary double vision.
| Cause Category | Description/Examples |
|---|---|
| Eye Muscle Problems | Imbalance, weakness, or paralysis in the eye muscles (diplopia and paralytic strabismus). Problems with muscles responsible for outward gaze or divergence insufficiency can cause double vision at distance. |
| Nerve Problems | Palsies in the cranial nerves that control eye muscles (especially the 6th nerve, which controls outward gaze) can lead to double vision in distance viewing. |
| Strabismus (Squint) | Eye misalignment, which becomes more pronounced in some types, particularly when looking into the distance. In cases of diplopia and paralytic strabismus, double vision caused by nerve damage leading to muscle paralysis may be greater in certain directions of gaze (including distance). |
| Neurological Diseases (Double Vision Neurology) | Conditions such as Multiple Sclerosis (MS), Myasthenia Gravis, stroke, brain tumors, and increased intracranial pressure can affect the nerves controlling eye movements, causing double vision. |
| Cataract | Although it usually causes monocular (single-eye) double vision, it can affect distance vision by impairing overall visual quality due to the blurriness and light scattering it creates. |
| Hypertension Double Vision | High blood pressure can damage the small blood vessels supplying the eye nerves, leading to temporary nerve palsies and subsequent double vision. |
| Eye Strain Double Vision | Prolonged visual effort, especially with uncorrected refractive errors, can cause eye muscle fatigue and temporary double vision. |
| Dry Eye Double Vision | Dryness on the eye surface can impair visual quality during distance viewing, especially in windy or air-conditioned environments, leading to a wavy or shadowy double vision sensation. |
| Lazy Eye Double Vision (Amblyopia and Diplopia) | Amblyopia is usually associated with the brain suppressing one eye to prevent double vision. However, if the underlying condition causing amblyopia (e.g., strabismus) persists or is treated (especially in older age), double vision may emerge or become noticeable. |
| Thyroid Eye Disease (Graves’ Ophthalmopathy) | In this condition, associated with an overactive thyroid gland, the eye muscles and surrounding tissues swell and stiffen. This restricts eye movement, causing binocular double vision, particularly in certain directions of gaze (including distance). |
| Trauma | Head or eye injuries can damage nerves or muscles, leading to permanent or temporary double vision. |
When the causes of double vision are examined, some are temporary (eye strain, certain medication side effects, mild nerve damage from controlled diabetes or hypertension), while others are permanent or require treatment (structural strabismus, severe nerve damage, cataracts, thyroid eye disease). Even if temporary, investigating the cause of double vision is important to rule out a potentially serious underlying condition.
Diplopia Treatment
One of the most pressing questions for patients is, “Is there a treatment for double vision?” The answer is a definitive yes; in most cases, double vision is a treatable symptom. However, the treatment for diplopia depends entirely on the underlying cause. The primary goal of treatment is always to eliminate this root cause.
Methods Used in Diplopia Treatment:
- Observation: If the double vision is due to temporary causes like eye strain or a mild nerve palsy from a condition like diabetes that is expected to resolve on its own, your doctor may recommend only monitoring for a period.
- Treatment of the Underlying Disease: This is the most important step. Treatments aimed at the cause, such as controlling diabetes, managing hypertension, treating thyroid disease, using medication for Myasthenia Gravis, treating infections with antibiotics, or surgically removing a tumor, often eliminate the double vision as well.
- Correction of Refractive Errors (for Monocular Diplopia):
- Eyeglasses or Contact Lenses: Monocular double vision caused by refractive errors like astigmatism can be corrected with appropriate glasses or lenses.
- Laser Surgery: Can reshape the cornea to correct irregularities like astigmatism and resolve monocular diplopia.
- Management of Ocular Surface Disease: Treating dry eye with methods like artificial tears or punctal plugs can improve the associated monocular double vision.
- Cataract Surgery: The definitive treatment for cataract-induced monocular diplopia is the surgical removal of the cloudy lens and its replacement with an artificial one.
- Prismatic Glasses: These special glasses use prisms to redirect the light entering the eye, allowing the images from both eyes to be perceived by the brain as a single image again. They are used especially in cases of stable, permanent binocular diplopia that is not too large in angle. They can be temporary (Fresnel prisms applied to glasses) or permanent.
- Vision Therapy (Orthoptic Treatment): These are exercises aimed at improving the coordination of the eye muscles and the brain’s ability to fuse images. They are particularly effective for conditions that cause diplopia on focusing, such as convergence insufficiency.
- Occlusion (Patching): Covering one eye is the simplest method to instantly eliminate binocular double vision. However, it is not a long-term solution as it prevents three-dimensional vision. It is generally used for temporary relief until other treatments become effective or in cases of permanent double vision.
- Botulinum Toxin (Botox) Injections: Based on the principle of temporarily weakening an eye muscle by injecting it. This balances the effect of the opposing muscle and corrects the eye alignment. It is used especially in acute nerve palsies (particularly 6th nerve palsy) and some types of strabismus.
- Surgical Intervention (Strabismus Surgery): In cases of permanent binocular diplopia that do not resolve with methods like prisms or Botox, surgical treatment is often required. In strabismus surgery, the power of the muscles that move the eye is adjusted (weakening, strengthening) or their points of attachment are changed to realign the eyes. In cases of paralytic strabismus, where a muscle is completely paralyzed, transposition surgeries can be performed to have other muscles take over the function of the paralyzed one.
The choice of treatment depends on many factors, such as the size and stability of the deviation, the cause of the double vision, and the patient’s age and general health, and is typically made by a strabismus specialist or an ophthalmologist experienced in neuro-ophthalmology.
Symptoms and Diagnosis of Diplopia
While double vision (diplopia) is a symptom in itself, it often appears with other symptoms, and the diagnostic process involves a careful evaluation of these signs and findings.
Symptoms: The most basic symptom of diplopia is the perception of a single object as two. This dual image can be side-by-side (horizontal diplopia), one on top of the other (vertical diplopia), or diagonal/tilted. Sometimes, one image is clearer while the other is a fainter, ghost-like image. In addition to double vision, the following symptoms may also be present:
- Headache
- Dizziness and Loss of Balance
- Pain in the Eyes (especially with eye movement)
- Eye Strain
- Nausea
- Drooping Eyelid (Ptosis)
- Misaligned Eyes (Strabismus)
- Abnormal Head Posture: The person may unconsciously tilt or turn their head to reduce or eliminate the double vision.
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Diagnosis: The diplopia examination aims to determine the cause and type of double vision. The diagnostic process usually includes the following steps:
- Detailed Patient History
- Comprehensive Eye Examination: This includes measuring visual acuity, assessing for refractive errors, and performing a simple cover test. A slit-lamp examination is used to investigate causes of monocular diplopia like cataracts, and a fundus examination evaluates the retina and optic nerve.
- Evaluation of Eye Movements: Your doctor will ask you to move your eyes in different directions to determine which muscle or muscles have weakness or restriction.
- Ancillary Tests (If necessary):
- Blood Tests: To investigate systemic diseases like diabetes, thyroid disorders, or Myasthenia Gravis.
- Imaging Studies: Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) of the brain and orbits to detect structural problems like tumors, stroke, or nerve compression.
- Neurological Consultation: An evaluation by a neurologist may be requested, especially in cases of binocular diplopia or when a neurological cause is suspected.
- Special Tests: A Tensilon test or Electromyography (EMG) may be performed if Myasthenia Gravis is suspected. Rarely, a lumbar puncture may be needed.
It should not be forgotten that sudden-onset double vision, especially when accompanied by additional symptoms such as severe headache, speech impairment, body weakness, or loss of balance, can be a sign of a serious condition requiring emergency medical intervention (such as a stroke or aneurysm rupture). In such cases, an ophthalmologist must be consulted immediately.
How Does Double Vision Resolve?
The answer to “how does double vision get better?” or “how does double vision resolve?” again depends on the underlying cause and the effectiveness of the applied treatment.
- Spontaneous Resolution: Double vision due to temporary causes like eye strain, some medication effects, or mild nerve palsies related to controlled diabetes/hypertension can often resolve on its own within a few weeks or months once the underlying condition is controlled or the trigger is removed.
- Resolution with Treatment: Conditions causing monocular diplopia, such as cataracts or significant astigmatism, are generally completely resolved with appropriate treatment (surgery, glasses). In cases causing binocular diplopia, like strabismus, improvement or complete resolution can be achieved with interventions such as prism glasses, Botox, or surgery.
- Variable Prognosis: The answer to “will double vision get better?” may not always be positive, or the process can be variable. In cases of nerve damage due to trauma, recovery may not be complete. In chronic neurological diseases like MS or Myasthenia Gravis, double vision can occur in attacks or fluctuate throughout the day. Double vision after strabismus surgery is usually temporary but can rarely be permanent or require a second operation.
Therefore, it is important to have realistic expectations during the treatment process and to adhere to the follow-up schedule recommended by your ophthalmologist. The recovery process can sometimes be long and may require patience.
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