Childhood strabismus
Does your child have a squint? Is it constant or just occasional? Always in the same eye or alternately? This is strabismus. This condition affects 4% of children in developed countries and 2.5% of children in France. Strabismus is a deviation of one eye from the other. When the patient looks at you from the front, only one eye is focused: this is the "fixating" or dominant eye. The other eye is therefore deviated (not looking straight ahead) and is the "non-fixating" or dominated eye. This misalignment of the eyes is most often due to a difference in refractive power between the two eyes (one eye "working" harder than the other), but sometimes it is due to an eye condition that requires treatment. Regardless of the cause of the strabismus, the development of vision can be affected, which is why an ophthalmological consultation is essential in all cases.
Characteristics of strabismus in children
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Childhood strabismus most often appears in the first two years of life.
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The simplest and most reliable way to observe strabismus is to show a dim light source to the child (who will instinctively fixate on it), then look at the reflection of the light on their eyes: if the point of light is reflected in the middle of the two pupils, then there is no strabismus.
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In cases of strabismus, the reflection of light will be seen in the center of the pupil of the fixating eye, and on one side of the pupil of the deviated eye. This pupillary reflection technique is even more valuable in a frontal photograph.
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Strabismus can be unilateral (it is always the same eye that is deviated) or alternating (depending on the time, the deviated eye can be either the right or the left).
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It can be permanent (the eye is permanently deviated), in which case it is called tropia. If the strabismus is latent, appearing only occasionally, for example in a context of fatigue, it is called phoria.
The direction of deviation of the dominated eye can be towards:
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Inward deviation (esophoria or esotropia): this is called convergent strabismus, where the dominant eye is deviated towards the nose. This is the most common case in children (90%).
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External deviation (exophoria or exotropia): this is called divergent strabismus, where the dominant eye is deviated towards the temple.
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The top (hyperphoria or hypertropia)
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The bottom (hypophoria or hypotropia)
False strabismus and epicanthus
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When children are under one year old, their eyes may appear to be misaligned even though they aren't. This is called "pseudostrabismus." This appearance is due to the fold of skin on the child's upper eyelid, which curves towards the inner corner of the nose.
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In this situation, the reflections on the child's pupil are symmetrical. This appearance of strabismus will disappear as your child's face develops.
The causes of strabismus in children
The two main causes of strabismus in children are:
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Anisometropia – This is the difference in refractive power between a child's two eyes. In other words, one eye needs a stronger correction than the other. Consequently, that eye has to work harder to focus than the other, causing it to deviate.
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An organic anomaly – Any disease or malformation of one of the eyes that can impair vision can cause strabismus. In this case, the affected eye is deviated, while the healthy eye maintains focus. This is most often a congenital cataract.
Several factors increase the risk of developing strabismus: prematurity, low birth weight, exposure to alcohol or tobacco during pregnancy, associated neurological disorders, and genetic abnormalities.
The consequences of strabismus in children
Strabismus has three main consequences:
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Lack of stereoscopy – Loss or absence of binocular vision development: the child does not develop the ability to perceive depth (no 3D vision). Indeed, depth perception is only possible if both eyes are coordinated. The earlier the onset of strabismus, the less likely the development of normal binocular vision becomes.
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Amblyopia – This is the decrease in visual acuity of the deviated eye, resulting from a lack of visual stimulation, because the child does not use this eye to see! This eye, which becomes "lazy," will therefore see less well than the healthy eye, even with the wearing of corrective glasses.
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Aesthetics – The unsightly nature of certain strabismus can have a social impact, with more or less marked psychological consequences.
When and why consult a doctor?
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If there is any doubt about the presence of strabismus in a child, an ophthalmological consultation is recommended regardless of age. In all cases, a fundus examination will be performed to rule out any underlying pathology, such as congenital cataracts.
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However, most cases of intermittent strabismus observed in infants under 3 months of age are benign and transient, due to the immaturity of the visual system. Strabismus should only be suspected after 6 months of age if the deviation is constant and always affects the same eye. Similarly, divergent strabismus (exophoria or exotropia) is always suspicious: a consultation is recommended regardless of the circumstances or age.
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A white (leukocoria) or orange-red pupillary reflection on photos is an alarming sign because it can reveal an organic abnormality of the eye: it is an urgent reason for consultation in ophthalmology.
Treatment of strabismus in children
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The challenge is to treat the cause of strabismus and then the consequences.
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In the case of an organic abnormality, the treatment is specific: surgery if it is a cataract, for example.
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In cases of anisometropia, treatment consists of prescribing glasses that fully correct the child's refractive error (hyperopia, myopia, astigmatism). The correct correction is determined after instilling cycloplegic eye drops into the child's eyes (5 to 7 days before the examination for Atropine, and 45 to 60 minutes before the examination for Skiacol).
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In most cases, wearing appropriate glasses can reduce or even eliminate the deviation of the eye, since the correction allows it to stop "working more than the other".
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In cases of amblyopia associated with strabismus, constant wearing of glasses is also part of the treatment, in addition to occlusion of the healthy eye.
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If strabismus persists despite wearing glasses, surgery may be offered, but it depends on the degree of deviation of the dominant eye, which must be quite significant and stable over time.
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In the case of phoria (intermittent strabismus), orthoptic rehabilitation can help to eliminate the deviation of the eye and also provide visual comfort.
Monitoring and development of strabismus in children
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The total optical correction (administered under Skiacol or Atropine) is by definition maximal, and therefore may be poorly tolerated by the child at first. This adaptation period is often shortened by explanations from the doctor, and then by the parents who reassure the child.
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The degree of strabismus deviation changes over time. It is therefore important to have regular checkups every 6 to 12 months, depending on the child's age.
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Follow-up care is provided jointly by the ophthalmologist, who will adjust the optical correction using examinations with cycloplegic eye drops (Skiacol or Atropine), and the orthoptist, who will conduct the assessments. The orthoptic assessment will also help determine if surgery is indicated and if this option is being considered.
Conclusion
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The suspicion of strabismus in a child should systematically prompt an ophthalmological consultation.
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Most of the time, the cause is a refractive imbalance: the prescription of suitable glasses (made after a regular visual examination under cycloplegic eye drops) therefore constitutes a major part of its management.
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However, some strabismus may reveal an ophthalmological condition requiring rapid treatment (congenital cataract, retinoblastoma).
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It is also important to screen for and treat possible amblyopia, which is frequently associated with it, and can become irreversible if not addressed in time.