By Eyecare NGOverview | Causes | Symptoms | Care & Management
Double vision, also known as diplopia is a condition where you see a single object as two.
Double vision can occur in various ways. It can occur with only one eye or with both eyes in use. It may be temporary or permanent and the images seen can either be lying side by side, one on top of the other, slightly slanted or overlapping each other. The onset of double vision may be sudden or it may occur for a while without complaints because the individual finds a way to suppress one of the images, for example, by tilting the head.
Normally, each eye sees an object independent of the other eye, forms its own image and sends signals to the brain where the two images from both eyes are fused together into one. This process results in single binocular vision (the perception of one image following the fusion of the separate images formed in the two eyes)
Causes of Double Vision
There are many causes of double vision ranging from the very minor ones to serious life-threatening conditions.
Refractive errors occur when light rays do not focus properly on the retina resulting in blurry vision. Refractive errors include myopia, hyperopia and astigmatism. They can cause double vision depending on the degree of the error especially when the defect is more in one eye compared to the other, (a condition known as anisometropia).
This is also known as squint or strabismus. It is a misalignment of the two eyes when looking at an object. This misalignment appears as a deviation of the eye. There are different types of tropia:
- Esotropia – One or both eyes turn inwards towards the nose.
- Exotropia – One or both eyes turn outwards away from the nose.
- Hypertropia – One eye deviates upwards (above the line of vision).
- Hypotropia – One eye deviates downwards (below the line of vision).
Tropia normally happens early in life. Children with this condition tend to adopt some means to cope with double vision. They either tilt their head, turn their neck or close one eye. Sometimes, the brain suppresses the image from one of the eyes and this could result in amblyopia (lazy eye). It is important that all cases of squint in children are treated as soon as possible to avoid amblyopia.
Some corneal conditions such as keratoconus (conic cornea) and corneal scars can cause double vision because of the poor focusing of light rays on the retina.
Dry Eye Syndrome
Dry eye syndrome, a condition that results from poor quality or inadequate tear film can cause double vision due to inadequate lubrication of the cornea. Poorly lubricated cornea results in poor focusing of light on the retina. Double vision in dry eye syndrome is usually characterized by overlapping of images and tends to reduce or disappear with blinking.
Cataract and Partial Lens Dislocation
Cataracts are opacities of the lens. They cause double vision by scattering light that enters the eye. The scattering of light results in the formation of multiple images on the retina.
In partial dislocation of the lens, double vision occurs because the light rays that pass through the dislocated lens and the ones that pass through the area not covered by the lens form different images. This can be taken care of through cataract surgeries/lens extraction.
Cranial Nerve Palsy
The cranial nerves control the extraocular muscles of the eyes which play a role in the alignment of the eyes. Disorders of the cranial nerves can result in weakness or palsy and consequent misalignment of the eyes. Some conditions that may cause cranial nerve palsy include stroke, brain infection, tumours, head trauma/injury, bleeding in the brain, aneurysms and multiple sclerosis, as well as vascular conditions such as diabetes mellitus and hypertension.
Ocular Muscle Disorders
Inflammation, paralysis or weakness of the extraocular muscles can interfere with their function of maintaining the alignment of the eyeballs. For instance, in the neuromuscular disease known as Myasthenia Gravis, the weakness and rapid fatigue of the muscles under voluntary control causes double vision.
Binocular Vision Anomalies
Binocular vision anomalies like convergence insufficiency and divergence excess can cause double vision particularly when the eyes are tired. In convergence insufficiency, the eye muscles have difficulty maintaining alignment when looking at a near object while in divergence excess the eye muscles have difficulty maintaining alignment while looking at a far object.
Symptoms Associated with Double Vision
The following symptoms may be experienced alongside double vision;
Care and Management of Double Vision
If you experience double vision, it is important to see an eye care professional. Diagnosing the cause of double vision is a key step to proper care and management of the condition responsible for it.
Here are some things to expect when you visit your eye doctor with a complaint of double vision;
Your eye doctor would normally ask questions that will help the diagnosis of the condition responsible for your double vision. Some questions you may be asked include;
- When did you first experience double vision? (That is, when did it start?)
- What other symptoms do you have?
- When do you experience double vision most? Is it in the morning, at the end of the day or when you are tired?
- Is the double vision there all the time or goes away after a while?
- What is the position of the images in relation to each other? Side by side (horizontal), one on top of the other (vertical), slightly tilted or obliquely positioned (skewed) or overlapping (ghosting)?
- How many images do you see when you close one eye?
- Do you tend to tilt your head or turn your neck to one side or close one eye to eliminate the double vision? Which side? (You may be asked to present some old pictures or your family may be asked about the head tilt because most people with this symptom usually don’t know that they tilt their head)
- Are the two images clear or is one blurry and the other clear?
- Does the image disappear or increase when you move your eyes at different positions of gaze such as up, down, left, right, up to the right, up to the left, down to the right and down to the left? Which position?
- Have you hit your head, fallen or been unconscious recently?
- Were you involved in an accident e. g. Car accident?
Comprehensive Eye Examination
- Visual acuity measurement: Your eye doctor will check how well you can see with each eye by asking you to read from a chart positioned about 6 metres or 20 feet away from you.
- Ocular motility test: He will assess how well your extraocular muscles are functioning and also measure the degree of misalignment if you have a squint.
- Refraction: The refractive power of your eyes may be evaluated to see if you need glasses.
- Binocular vision assessment: If your doctor suspects that your double vision is as a result of poor binocular vision; the full binocular vision tests will be carried out. This will include the measurement of phoria, fusional vergences, and other assessments.
- External and internal examination: Your external and internal ocular structures will be checked for abnormalities. The eyes may be dilated to help the doctor get a better view of the inside of your eyes. The quality and quantity of your tear film may be assessed using some special dyes.
- Computed tomography /magnetic resonance imaging (CT/MRI) scan: If your eye doctor suspects that your double vision may be due to some brain-related disorders, he/she may order a CT/MRI scan of your brain or refer you to a neurosurgeon or neurologist who will have that done and assessed.
Treatment for Double Vision
One or more of the following treatment options may be recommended for double vision depending on diagnosis:
- Optical devices: Glasses with prisms incorporated into them may be prescribed to eliminate double vision.
- Eyepatch: The use of eye patch may be recommended to help you cope with the symptom.
- Surgery: Surgery may be recommended to align the extraocular muscles of the eye or to take care of cataracts and partially dislocated lens. Brain surgeries may be needed if double vision is caused by brain tumours and aneurysms.
- Medications: These may include drops and ointment for conditions like dry eyes.
- Vision training: This is usually recommended in binocular vision anomalies such as convergence insufficiency and in the management of squint.
- Referral for other medical causes: If no ocular cause of double vision is detected or you have other medical conditions that can cause double vision, your eye doctor will refer you to another healthcare practitioner such as a primary care physician or neurologist depending on the condition suspected. Your primary care physician or neurologist may prescribe medications for the treatment of underlying conditions like diabetes, hypertension and neurological disorders.