Strabismus: Causes, Symptoms & Treatment

Written by Vasileios Skouteris MD, FEBO, Ophthalmic Surgeon

Page contents

1. What is strabismus?
2. Causes of strabismus
3. Symptoms
4. Strabismus and amblyopia
5. How is strabismus diagnosed?
6. Strabismus treatment
7. Strabismus in children: when should you be concerned?
8. When to see an ophthalmologist
9. Types of strabismus
10. Pseudostrabismus: when the eyes only look crossed
11. Strabismus in adults and double vision
12. Prisms and botulinum toxin
13. Strabismus surgery in detail
14. Stereoscopic vision: why alignment matters
15. Strabismus and self-confidence
16. What a strabismus examination involves
17. How to help your child with treatment
18. Myths about strabismus
19. Long-term follow-up
20. Frequently Asked Questions about Strabismus

Strabismus, also known as a squint or crossed eyes, is a condition in which the two eyes do not look in the same direction at the same time. While one eye looks at the target, the other turns inwards, outwards, upwards or downwards. It is more common in children, but it also affects adults.

What is strabismus?

To see a single, three-dimensional image, the six muscles that move each eye must work together perfectly, so that both eyes point at the same spot. The brain combines the two images into one, a function called binocular vision. When this alignment is lost, strabismus develops.

Depending on the direction of the deviation, strabismus is classified as:

• Esotropia: the eye turns inwards, towards the nose.
• Exotropia: the eye turns outwards.
• Hypertropia or hypotropia: one eye sits higher or lower than the other.

Strabismus can be constant or intermittent, meaning it only appears with tiredness, illness or when the child is looking into the distance. In babies there is also pseudostrabismus: a wide bridge of the nose covers part of the white of the eye and gives the impression that the eyes “turn in”, when in fact they are aligned. The ophthalmologist is the one who can tell the difference.

Causes of strabismus

In many cases no single cause is found. The most common factors are:

• Family history: strabismus is more common in families with a history of strabismus or amblyopia.
• Long-sightedness: a child with high hyperopia has to make a great effort to focus in order to see clearly. This effort is linked to the eyes converging and can cause accommodative esotropia, usually between the ages of 2 and 4.
• A large difference in prescription between the two eyes, so that one eye sees blurred and “drifts”.
• Premature birth and low birth weight.
• Neurological conditions and syndromes, such as cerebral palsy.
• Poor vision in one eye from another cause, such as a congenital cataract or a retinal condition.

In adults, strabismus can be caused by paralysis of a cranial nerve, often in the setting of diabetes or high blood pressure, by thyroid eye disease, by an injury to the eye socket, or by the decompensation of a squint that has been present since childhood.

Symptoms

In children, the main sign is what parents notice: an eye that wanders, either constantly or from time to time. Other signs are:

• closing or rubbing one eye, especially in the sun,
• tilting or turning the head to look at something,
• clumsiness or difficulty judging distances.

Young children rarely see double, because their brain “switches off” the image from the deviating eye. Adults, on the other hand, often have double vision (diplopia), eye strain, headaches and difficulty reading.

Strabismus and amblyopia

Amblyopia, the so-called “lazy eye”, is reduced vision in an eye that did not develop properly in childhood, even though the eye itself is healthy. When a child has strabismus, the brain ignores the image from the deviating eye to avoid double vision. If this continues, the eye does not develop full vision.

Vision matures mainly up to the age of 7-8. The earlier amblyopia is treated, the better the results. Later on, improvement is usually limited.

How is strabismus diagnosed?

The examination is adapted to the patient’s age and includes:

• measuring the visual acuity of each eye with pictures or letters,
• the cover test, in which each eye is covered in turn and the movement of the other eye is observed,
• measuring the angle of deviation with prisms,
• checking eye movements in all directions and stereoscopic (3D) vision,
• measuring the refraction after cycloplegic drops, which relax focusing and reveal the true level of long-sightedness,
• fundoscopy, to rule out a condition at the back of the eye.

When strabismus appears suddenly in an adult, neurological assessment or imaging may also be needed.

Strabismus treatment

The aims of treatment are good vision in each eye, alignment of the eyes and, where possible, restoring the way they work together. The order of the steps depends on the type of strabismus and the patient’s age.

Glasses

These are often the first step. In accommodative esotropia, glasses that correct the long-sightedness can fully align the eyes without any other treatment. They must be worn all the time, as instructed by the ophthalmologist.

Eye patching

The eye that sees better is covered with a special adhesive patch for a certain number of hours a day, so that the brain is “forced” to use the amblyopic eye. In some children, drops that temporarily blur the good eye are used instead. The treatment needs consistency and regular check-ups.

Exercises

Orthoptic exercises help with specific forms, such as convergence insufficiency, where the eyes struggle to converge for close reading. They do not replace glasses or surgery when these are needed.

Surgical correction

When strabismus persists, surgery strengthens or weakens one or more of the muscles that move the eye. The eye is not taken out of its socket, and the operation is usually done as a day case, under general anaesthetic in children. Some patients need a second operation, and glasses or patching often continue afterwards. In adults, correction can improve double vision and appearance.

Strabismus in children: when should you be concerned?

During the first 3-4 months of life, it is common for a baby’s eyes to drift occasionally. After this age, any deviation needs to be examined. Every child should be seen by an ophthalmologist at least once before starting school, even if there is no obvious problem. For the timing of eye checks, see our article on when a paediatric eye examination is recommended and our page on paediatric ophthalmology.

When to see an ophthalmologist

• If your child’s eye turns after the fourth month of life, even occasionally.
• If your child closes one eye, tilts their head or gets very close to things to see them.
• If in flash photographs one pupil looks white or different from the other. This needs to be examined without delay.
• If, as an adult, you suddenly develop double vision or a squint, seek help the same day, as there may be an underlying neurological cause.

For a strabismus assessment for children and adults at the clinic in Neo Psychiko, Athens, book an appointment.

Types of strabismus

Strabismus is described according to the direction in which the eye turns and whether the deviation is constant or only appears at certain times.

• Esotropia: The eye turns inwards, towards the nose. This is the most common form in young children.
• Exotropia: The eye turns outwards. It is often intermittent and shows when the child is tired, daydreaming or looking into the distance.
• Hypertropia and hypotropia: One eye is higher or lower than the other. It is often accompanied by a head tilt.

Infantile esotropia

This appears during the first six months of life, with a large angle of deviation. It is not corrected with glasses and usually needs surgery at a young age, to give the brain the chance to develop cooperation between the two eyes.

Refractive (accommodative) esotropia

This usually appears between the ages of 2 and 4 in children with long-sightedness. The child’s effort to focus in order to see clearly “pulls” the eyes inwards. The right glasses can straighten the eyes completely, without surgery. That is why it is important for the glasses to be worn all day.

Intermittent exotropia

One eye “drifts” outwards at times, often in the sun, when the child typically closes one eye. It is monitored regularly and, if the deviation becomes more frequent or larger, it is treated surgically.

Pseudostrabismus: when the eyes only look crossed

Many babies have a wide nasal bridge and a fold of skin at the inner corner of the eyes. This hides part of the white of the eye on the nose side and gives the impression that the eyes are looking inwards, especially when the child looks to the side. Pseudostrabismus fades as the face develops. However, it can only be told apart from true strabismus by an examination, so we should not assume it “will pass” without the child being seen by an ophthalmologist.

Strabismus in adults and double vision

When strabismus appears in adult life, the brain can no longer “switch off” the image from one eye as it does in children. The result is diplopia, meaning the patient sees two images. The most common causes are:

• Paralysis of a cranial nerve that moves the eye muscles, often in people with diabetes or high blood pressure because of microvascular damage. Many of these resolve on their own within a few months.
• Thyroid eye disease, in which the eye muscles swell and lose their elasticity.
• Myasthenia gravis, with double vision and a drooping eyelid that get worse towards the end of the day.
• Recurrence of a childhood squint that had been controlled for years.
• Injury or previous eye surgery.

Important: sudden double vision, especially with headache, a drooping eyelid, a dilated pupil or other neurological symptoms, is an emergency and needs assessment in hospital the same day.

Prisms and botulinum toxin

For small deviations, mainly in adults with double vision, prisms in glasses shift the image so that it matches in both eyes and the double image disappears. They can be temporary, stuck onto the lens while we wait for the condition to stabilise, or built into the lenses.

Botulinum toxin, familiar from cosmetic treatments, is also used in strabismus. Injected into an eye muscle, it relaxes the muscle temporarily so that the eye straightens. It is useful in selected cases, such as acute nerve palsy or small deviations.

Strabismus surgery in detail

Strabismus surgery is performed on the muscles that move the eye, on the outer surface of the eyeball. The eye is not “taken out” of its position, as many people fear. The surgeon changes the attachment point of one or more muscles, to weaken or strengthen their action and align the eyes.

• Anaesthesia: In children it is done under general anaesthetic. In adults it can also be done under local anaesthetic.
• Duration: Usually 30 minutes to an hour, depending on the number of muscles.
• Hospital stay: The patient goes home the same day.
• After surgery: The eye is red and uncomfortable for a few days. Eye drops are prescribed and the redness fades within 2 to 3 weeks.
• Getting back to normal: Children return to school after about a week. Swimming after two weeks.

In adults, adjustable sutures can be used, which allow a small correction of the eye’s position a few hours after surgery, when the patient is awake and can cooperate. Some patients need a second operation in the future, especially with large or complex deviations.

Stereoscopic vision: why alignment matters

When both eyes look at the same point, the brain combines the two slightly different images and creates a sense of depth. This stereoscopic vision helps us catch a ball, pour water into a glass and judge distances when driving. It develops in the first years of life, which is why aligning the eyes early in children gives them the best chance of good cooperation between the two eyes.

Strabismus and self-confidence

Strabismus also affects social life. Children may be teased, while adults report difficulty with eye contact, in job interviews or in photographs. Correcting strabismus in adults is not a “cosmetic luxury”: it restores normal communication and often improves the field of vision too. It is never too late to discuss your options.

What a strabismus examination involves

The examination starts with observation: how the child holds their head, how the eyes move in all directions, and whether the deviation changes when they look near or far. With the cover test, where one eye is covered in turn, the ophthalmologist sees whether and how much the other eye moves to “catch” the target. The angle of the squint is measured with prisms, so that treatment can be planned precisely.

Next, the vision of each eye is checked separately, stereoscopic vision is tested with special cards, and the prescription is measured after cycloplegia. Finally, fundoscopy is performed, because occasionally strabismus is the first sign of a problem at the back of the eye. In adults with double vision, additional blood tests or imaging of the brain and eye sockets may be needed.

How to help your child with treatment

• Make glasses part of the routine, like brushing teeth: your child puts them on as soon as they wake up.
• Let the teacher or nursery staff know, so they can encourage your child.
• During patching hours, suggest favourite activities that involve close-up work.
• Reward consistency with a simple sticker chart.
• Do not skip follow-up visits, even when the eyes look straight.

Myths about strabismus

• “It will straighten out on its own as they grow.” True strabismus does not correct itself. Waiting can cost the child the vision in one eye.
• “Surgery is only done in children.” The operation is performed safely at any age, and in adults it improves double vision, the field of vision and appearance.
• “If they start wearing glasses, they will need them forever.” Glasses do not create dependence. The prescription changes as the child grows and is adjusted accordingly.
• “Eye exercises correct every squint.” Orthoptic exercises help with specific forms, such as convergence insufficiency, but they do not correct a constant deviation.
• “Strabismus is only a cosmetic problem.” It affects how vision develops and depth perception and, in adults, causes double vision.

Long-term follow-up

Even after successful treatment or surgery, children with strabismus need regular check-ups until their vision has finished developing, at around 8 to 10 years of age. Amblyopia can return if treatment stops too early, and the glasses prescription changes with age. In adults, visits are adjusted to the cause of the strabismus and how stable the deviation is. If, after surgery, you notice the eye starting to turn again or double vision appears, book an extra appointment without waiting for your scheduled check-up. Early assessment always makes the solution simpler.

To book an appointment, call 210 677 0007.

Frequently Asked Questions about Strabismus

Medically reviewed by: Dr. Vasileios Skouteris MD, FEBO