Exotropia

What is Exotropia?

Exotropia is a condition where the eyes move away from the nose. This can either be something a person is born with (congenital) or something they develop later in life (acquired). Depending on how the eyes move, exotropia can be classified as either concomitant or incomitant.

In concomitant exotropia, the extent to which the eyes deviate remains the same, no matter where the person is looking. In incomitant exotropia, the extent of eye deviation changes depending on the direction of the gaze. This type is often linked to restricted movement of the eyes, which can happen due to muscle paralysis or other limiting conditions.

There are several subtypes of concomitant exotropia, including those present at birth, those that develop without any clear reason, those caused by vision loss, or those that develop following surgery.

Incomitant exotropia can also take several forms, from those that result from nerve paralysis, to those with particular gaze patterns (like A, V, or X patterns), to those caused by physical restrictions on eye movement due to conditions like Duane retraction syndrome, thyroid myopathy, or following injury or surgery. There are grades in the severity of exotropia, ranging from mild (exophoria), to intermittent, to constant (exotropia).

In this simplified explanation, our main emphasis will be on explaining concomitant exotropia.

What Causes Exotropia?

The reason behind different types of outward eye turns (exodeviations) can vary.

Congenital (Infantile) Exotropia

Congenital (infantile) exotropia is when a child is born with their eyes turning outwards. This is not as common as the inverse condition, called congenital esotropia, where the eyes turn inwards. It’s often found with conditions that affect the face and skull (craniofacial abnormalities), a lack of pigmentation in the eyes (ocular albinism), or cerebral palsy.

Primary Exotropia

This condition is linked to either physical factors or related to the nervous system. Physical causes can include the orbit (the hollow space in the skull where the eye sits) shape and positioning, the distance between the pupils, characteristics of the extraocular muscles (the muscles that control eye movement), or the physical properties of the conjunctiva (a thin layer that covers the front of the eye) or tenon’s capsule (a thin tissue surrounding the eye). If there is an imbalance in the eye’s ability to turn towards or away from the nose, an outward turn can also occur. So, too much outward turn or not enough inward turn can lead to exotropia.

Sensory Exotropia

This usually occurs due to poor vision in one eye, more commonly when a person loses vision in one eye during infancy or adulthood. Possible causes can include differences in the power of the two eyes (anisometropia), cloudy areas in the cornea (the clear front surface of the eye) or changes in the lens, absence of the lens in one eye (unilateral aphakia), optic atrophy (damage to the optic nerve), or issues with the macula (the part of the eye responsible for sharp, central vision).

Consecutive Exotropia

Consecutive exotropia can result from either overcorrecting cross-eye (esotropia) during surgery or spontaneous change from esotropia to exotropia.

Risk Factors and Frequency for Exotropia

Exotropia, a condition where the eyes turn outward, has been the subject of various studies. A study conducted in Minnesota over ten years found that each year, 64.1 out of every 100,000 patients under the age of 19 were diagnosed with the condition. Among these cases, 86% were classified as intermittent exotropia or convergence insufficiency.

Another research effort that analyzed 56 different studies found the overall occurrence of exotropia to be 1.23%. This study also highlighted that the differences among exotropia patients increased with age. A separate study carried out on preschool-aged children in China found the condition to be somewhat more common, with a prevalence of 3.24%. In this particular demographic, there was no significant difference in occurrence related to age or sex.

• The majority of these patients (74.7%) were found to have “basic type” intermittent exotropia.
• Another 19.9% were identified as having “divergence excess” type.
• The least common type was “convergence weakness”, which was found in 5.4% of the study population.

Signs and Symptoms of Exotropia

Exotropia, a type of eye condition where one or both of the eyes turn outward, can be identified based on a person’s medical history and the specific characteristics of the condition they exhibit. Important information from the patient’s history includes when the condition began, how long it has been happening, the frequency and pattern of eye turning, and any contributing factors such as tiredness, unrelated health issues, bright lights, lack of attention, or drowsiness. Additionally, information on past eye conditions or significant pre-birth history, as well as any family history of eye turning, is important.

There are two main types of exotropia: congenital and intermittent. Congenital exotropia shows as a constant outward turn of more than 35 prism diopters and has poor fusional reserves. These patients have a higher risk of developing amblyopia (lazy eye) compared to those with intermittent exotropia. These patients also commonly need surgery and have associations like overactivity of the oblique muscle and dissociated vertical deviation.

Patients with intermittent exotropia may not show symptoms all the time. Sometimes, the only signs are occasional eye turns noticed by people around the patient. Other symptoms may include:

• Transient diplopia: Temporary double vision, which typically disappears as the eyes learn to suppress the double image.
• Diplophotobia: The tendency to close one eye in bright light to prevent double vision.
• Asthenopia: Eye strain, headaches, or other related symptoms, especially after prolonged reading.
• Micropsia: An unusual symptom where things look smaller than they should, due to the accommodative convergence aiming to control the outward turn of the eye.
• Exodeviation: The most commonly reported symptom from parents noticing the deviation in their child’s eyes, usually starting with distance and progressing to near, becoming more and more constant.

Progression of exotropia is affected by several factors such as age, loss of accommodation power, development of sensory adaptations, and divergence of orbits with age. There have been various classification systems for intermittent exotropia based on near and distance deviations.

The Newcastle scoring system is another way of assessing control among patients with intermittent exotropia. It includes scores for control at home and in the clinic, both for near and distance conditions.

• Home Control: Ranges from never noticed to frequently noticed squinting or closing one eye.
• Clinic Control for Near: Ranges from squinting only after a cover test and returning to normal without blinking to spontaneously squinting.
• Clinic Control for Distance: Ranges from squinting only after a cover test and returning to normal without blinking to spontaneously squinting.

The total score is the sum of all the individual scores from home and clinic control.

Testing for Exotropia

If you have exotropia, a condition where one or both of your eyes turn outward, it’s crucial to have a detailed eye exam. Here’s what you might expect during your check-up:

* Checking how well you can see: Your doctor will test your visual acuity or eye-fixation patterns using methods suitable for your age. They’ll also check if there are differences in the prescription of both eyes (anisometropia) or lazy eye (amblyopia).
* Repeated tests to measure the shape of your eyes: You might have to undergo a cycloplegic refraction test every six months if your eyes are squinting. This test helps the doctor determine your prescription by temporarily relaxing the focusing muscles inside your eyes.
* Alignment assessments: The doctor may perform alignment tests, known as the Corneal reflex/Hirschberg test and the cover test, at various distances to check how your eyes line up. This helps to see how much your eyes are misaligned and if breaking the alignment affects your vision.
* In-depth alignment tests: A prism cover test lets the doctor look at your eye movements in all directions and at various distances. They’ll also check if the degree of your eye turn decreases in the left or right gaze (lateral gaze incomitance) or if there are any issues related to an A or V pattern in your eye movements.
* Binocular single vision test (BSV): This essential test checks if your eyes can work together to give you a single image for both near and far distances. It must be repeated at every visit.
* Stereopsis test: This test, done during the phoric phase, checks your ability to perceive depth. If your ability to see objects in three dimensions continuously reduces kind of rapidly, it might be a sign that you need surgery.
* Occlusion test: If your eyes tend to turn more outward in the distance only or more so than at a nearer distance, an occlusion test can help. The doctor will cover one eye for at least 45 minutes before measuring the eye’s turn, to differentiate between simulated divergence excess and true divergence excess exotropia.
* Lens test with +3 diopters: The doctor will measure the eye turn with and without a +3 diopter lens in front of the wandering eye. This test helps the doctor predict how your eyes might respond to certain types of glasses if surgery results in overcorrection.
* Fusional amplitudes test: This test measures your eye muscles’ ability to bring your eyes together (convergence) or move apart (divergence) if you have intermittent exotropia (when exotropia happens occasionally). Most patients with intermittent exotropia are quite good at converging their eyes for near targets and poor to good for far ones. The ability to diverge is generally normal.

Treatment Options for Exotropia

Exotropia is a condition that causes an outward turning of the eye, and the way it’s treated depends on the type and any other eye issues a person might have.

In cases of congenital exotropia, which is present at birth, treatment should start as soon as possible. Eye exercises should be encouraged to treat a weaker eye, also known as amblyopia. After the child is six months old, surgery might be recommended and is usually done before they’re two years old. This could involve adjusting the muscles that move the eye in the weaker eye, to help improve alignment.

Intermittent exotropia, another form, can come and go. Treatments prior to considering surgery can include trying to correct any issues with eyesight, like near or farsightedness, or an unequal focus between both eyes. Special glasses can assist in improving control of the eye. In patients with a high AC/A ratio, increasing the power of the lenses stimulate the focusing mechanism of the eye which aids in resolving the problem. Additionally, with the help of eye patches or other methods, some exercises can help to train the eyes to work together correctly, and possibly prevent the need for surgery. In some cases, prisms can be used in glasses to help the eyes work together, though this is less common.

If the problem happens for more than half of the person’s waking hours or if other symptoms worsen, surgery may be needed. The choice of surgery will depend on various factors such as the degree and type of Exotropia, patient’s choice, and the surgeon’s experience. Botulinum toxin, type A, also known as Botox, has been evaluated as an alternative treatment, with findings that it can be almost as effective as surgery.

In some instances where a person has exotropia due to being unable to see out of one eye, the goal is mainly for the eyes to look aligned, to improve their appearance and quality of life. In these cases, the usual choice of surgery is to adjust the muscles that control eye movement in the weaker eye.

For consecutive exotropia, this happens after a person has had surgery to correct an inward turning eye, the method of treatment should always be discussed. Initially, any issues with eyesight should be addressed, and a trial of eye exercises to improve the weaker eye might also be recommended. It’s then possible to assess whether the patient is capable of using both their eyes together. The way the patient feels about their appearance can then determine the next step. If they’re happy with their appearance, close monitoring might be the only advice. If not, corrections could focus on appearance through surgery.

In conclusion, treating exotropia is complex, and every patient’s therapy should be individualized based on their needs.

What else can Exotropia be?

When diagnosing exotropia, a type of eye condition, doctors typically categorize the condition into two main types and consider possible subtypes for each one.

The first type is Comitant Exotropia, which includes potential subtypes such as:

• Decompensated intermittent exotropia
• Sensory exotropia
• Consecutive exotropia
• Convergence insufficiency
• Paralysis

The second type is Incomitant Exotropia, which can manifest as:

• Third nerve palsy
• Duane retraction syndrome
• Crouzon syndrome
• Restrictive pathologies (such as thyroid eye disease, medial wall blowout fracture, myositis, and myasthenia gravis)

It’s important for the doctor to recognize these potential subtypes to accurately diagnose and treat exotropia.

What to expect with Exotropia

The long-term success of either non-surgical or surgical treatment in aligning your eyes depends on several key factors. These factors can help predict what the long-term outcomes might be:

* Control of eye “fusion” before surgery – Fusion refers to your eyes’ ability to work together to form a single image. Good fusion control can lead to better results after the operation.

* How long your eyes have been misaligned – generally, the longer the period between when your eyes started to deviate (exodeviation) and when treatment began, the higher the chances for the misalignment to come back.

* Strong ongoing fusion – If your eyes can maintain the ability to work together well after the surgery, you will likely have better results.

* Adherence to correcting any refractive error (problems with bending of light in the eye) and performing regular vision exercises (orthoptics) can also enhance the alignment of your eyes. Consistency in these practices means you are more likely to maintain better alignment.

Possible Complications When Diagnosed with Exotropia

Exotropia, a condition in which the eyes diverge or turn outward, can cause several complications depending on its stage and manageability. The complications may include frequent headaches, issues with long reading periods, eye fatigue, and blurred vision. If not addressed at the early stages, patients may see their condition progress from exophoria to intermittent exotropia and ultimately to permanent exotropia. As this condition progresses, the ability to merge both visual fields into one image (fusional capacity) declines, leading to potential vision problems like the loss of binocular vision, depth perception (stereopsis), and in severe cases, lazy eye (amblyopia).

In addition to complications directly linked to exotropia, patients also run a higher risk of developing unrelated conditions like attention deficit hyperactivity disorder, learning difficulties, a brief attention span, social inhibitions, and dyslexia.

When it comes to surgery for exotropia, the risks are similar to those associated with any other eye muscle correction procedure. Risks related to anesthesia include potentially severe reactions like malignant hyperthermia, a heart reflex triggered by stress in the eye (oculocardiac reflex), and severe allergic reactions (anaphylaxis). Surgical risks include issues with eye muscle, certain capsular tissue protrusions, unintentional movement of a specific eye part (plica semilunaris), and perforation of the thick layer covering the eyeball (scleral perforation). Immediately following surgery, patients might encounter issues like swelling of the clear skin on the eye or the eyelids (chemosis or lid edema), complications due to the body’s response to stitches, cyst formation, changes in the blood supply to the front of the eye (anterior segment ischemia), undercorrection or overcorrection of the eye’s alignment, specific post-surgical syndromes, double vision, eyelid issue, and in rare cases, inflammation of the inner layers of the eye (endophthalmitis).

Common Complications:

• Frequent headaches
• Issues with long reading periods
• Eye fatigue
• Blurred vision
• Progression to permanent exotropia
• Loss of binocular vision
• Loss of stereopsis
• Amblyopia
• Attention deficit hyperactivity disorder
• Learning difficulties
• Short attention span
• Social inhibitions
• Dyslexia
• Surgery-related complications
• Risks associated with anesthesia
• Surgical complications
• Post-surgical issues

Recovery from Exotropia

Post-surgery care for people who’ve had an eye operation should concentrate on checking the alignment of the eyes, spotting any sudden big misalignments, and the positioning of the conjunctiva (the clear, thin tissue that covers the front part of the eye). Some people with exotropia (a condition where one or both of the eyes turn outward) may experience double vision shortly after surgery – it’s important to keep an eye on this and have regular check-ups.

For most people, this double vision should get better within six weeks. If it doesn’t, temporary use of prism glasses or occlusion glasses (glasses that block or blur vision in one eye to help improve vision in the other eye) could be recommended. Surgeons usually prefer to give short-term eye drops that contain steroids and antibiotics, with or without painkillers. The treatment is decided on a case-by-case basis. Young children may be given doses of painkillers in the form of a liquid if needed.

Future check-ups will aim to assess the alignment of the eyes, the movement of the eyes, and fixing any underlying vision problems. People may need to continue with eye exercises to prevent the outward turn of the eyes from happening again.

Preventing Exotropia

When someone has exotropia, which is a type of eye condition where the eyes turn outward, it’s crucial to seek treatment promptly. Doing so helps to maintain the ability to see in three dimensions, a skill called stereopsis. The doctor will carry out a thorough eye examination to pinpoint the type of exotropia and plan the appropriate treatment.

Treatment may involve a non-invasive approach, for example, orthoptic exercises (eye exercises to improve vision), fusion exercises, and minus therapy. All of these can help to align both eyes properly and may delay the need for any kind of eye surgery.

It’s important for parents to know about this condition so that, if noticed in their children, they can seek an early diagnosis and start appropriate treatment. If the patient eventually needs surgery, they should be properly informed about its type and nature. Doctors should clearly describe that the surgery is mainly to improve appearance, and there could be some temporary side effects like pain, redness, swelling of the eyelid.

Any potential changes in the gap between the eyelids or remaining misalignment of the eyes should also be discussed. For those undergoing a type of surgery called “adjustable sutures”, the patient would be briefed beforehand about the need for adjustments and securing the sutures to prevent confusion after surgery. It’s equally important to discuss the possibility of seeing double immediately after surgery and the need for common glasses and more eye exercises, along with regular check-ups.

Patients with a particular type of exotropia, sensory exotropia, should be made aware of the possibility that the condition may return over the years. This is particularly true for patients who have poor vision in the eye that turns outward.