專家教學

Strabismus

Author: Vanessa Thai
Developmental and Behavioural Optometrist
Central Health Southside – Child Development Team

What Is It?

Strabismus, commonly known as a squint or crossed eyes, is a misalignment of the eyes. This means the eyes do not aim at the same point of interest. The misalignment can be horizontal, or vertical, and can even be rotatory.

Colloquially, the word “squint” means squeezing our eyelids together to see more clearly or when we are in bright lights. A strabismic squint means the eyes are not working together properly as a result of a vision problem.

Lazy eye versus squint

Lazy eye refers to amblyopia, or when vision is reduced in one eye, even with corrective glasses and the eye is structurally normal. This arises from a miscommunication between the brain and eye, sometimes caused by untreated strabismus. Strabismus quite commonly accompanies amblyopia, in other words, a “squint” eye is often also “lazy”.

Types of strabismus

  • Esotropia – one or both eyes turn It is often referred to as “crossed eyes.”
  • Exotropia – one or both eyes turn It’s sometimes called “wall-eyed.”
  • Hypertropia – one eye turns upward while the other remains in a straight-ahead
  • Hypotropia – one eye turns downward while the other remains aligned
  • Alternating strabismus – the misalignment can switch between the eyes
  • Accommodative esotropia – often associated with focusing problems and occurs when one or both eyes turn inward when trying to focus on close
When Does It Develop?

Strabismus can develop at different ages depending on the individual and the underlying causes range from infantile- to adult-onset.

Causes of Strabismus
  • Muscle imbalance – problems with the eye muscles that control eye movements can lead to misaligned eyes. When the muscles do not work together properly, one eye may turn inward, outward, upward, or downward.
  • Genetics – a family history of eye turns can increase the likelihood of developing the condition, suggesting a genetic component.
  • Refractive errors causing a blurred visual image – without clear vision, misalignment occurs
    • Myopia (shortsightedness) – trouble seeing clearly in the distance
    • Hyperopia (longsightedness) – trouble focusing up close
    • Astigmatism – the front of the eye is oval-shaped resulting in blurred vision at all distances
  • Neurological issues – certain neurological conditions or brain disorders can affect the coordination of eye muscles, leading to strabismus
  • Health conditions – some conditions like cerebral palsy, Down syndrome, or traumatic brain injuries can be associated with strabismus
  • Vision development problems – if the eyes do not learn to work together during childhood, it can result in strabismus

Infantile esotropia

Infantile esotropia is a specific type of strabismus or crossed eyes that occurs in infancy or early childhood. It is characterised by an inward deviation of one or both eyes. It typically becomes noticeable within the first six months of a child’s life but can occur up to age 2. This is considered an early-onset form of strabismus.

Unlike some other forms of strabismus that may come and go, infantile esotropia is typically constant, with one or both eyes turned inward all the time. In addition, the degree of misalignment in infantile esotropia is often substantial, with a marked inward turn of the affected eye or eyes. There is a high risk of developing amblyopia in the affected eye.

The exact cause of infantile esotropia is not fully understood, but it may be related to problems with the eye muscles, sensory development, or neurological factors, resulting in a miswiring of the vision pathway to the brain. Additionally, it is more commonly diagnosed in premature babies.

Treatment

Early diagnosis and intervention are crucial in addressing strabismus to achieve the best outcome.

Because the brain is presented with two completely separated images (one from the straight eye and the other from the strabismic eye), as a compensation mechanism, it often ignores the image from the misaligned eye to avoid experiencing double vision. Without the two eyes working together, depth perception will be lacking and the risk of developing amblyopia occurs as the brain may start to suppress the input from the misaligned eye.

Treatment options depend on the type and severity of the misalignment, its underlying causes, and the child’s age and overall eye health.

Common treatment options:

  • Spectacle glasses or contact lenses – if the eye turn is associated with refractive errors.
  • Vision therapy – a program of exercises and activities designed to improve eye coordination and control, often used to treat non-refractive forms of
  • Eye patching – supervised patching of the straight/better eye may be recommended to encourage the use of the weaker eye and improve its vision, particularly if amblyopia is present.
  • Atropine eye drops – used to blur the vision in the stronger eye temporarily, which can encourage the use of the affected eye.
  • Surgery – involves adjusting the length or position of the eye muscles to improve eye Surgery is often considered when other treatments have not been effective or for certain types of strabismus.
  • Combination treatment – an example is surgery followed by vision therapy or ongoing use of glasses or contact lenses.

Regular follow-ups with an optometrist are essential to monitor the progress and make necessary adjustments to the treatment plan.

Impact on vision

Not exclusive to childhood-onset strabismus, adult-onset strabismus can also have a significant impact on vision. When the eyes are misaligned resulting in double vision, everyday activities can be affected.

With smaller eye deviations, the brain will attempt to fuse the two images from each eye together. This extra effort can cause symptoms such as eye strain, fatigue, headaches, and difficulty with near visual tasks.

In addition to possible amblyopia, while not affected by double vision for untreated childhood-onset strabismic individuals, the condition can still affect their visual field. For example, esotropes will have a narrower field of view due to their inward eye deviation. On the other hand, exotropes will experience more glare with their outward eye deviation.

Untreated strabismus can also have psychological and aesthetic consequences, as it may create the appearance that the individual is daydreaming or not fully engaged with the listener or observer due to an apparent lack of eye contact.

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