Eye disorders: strabismus

By Cristiano Antonino On Jun 18, 2023

Of the most common eye disorders with the main characteristic of deviation of the visual axes, strabismus is the main one

This disorder can in fact be quite common, as 4% of children suffer from it and some of these cases, if treated with the correct timing, can be corrected.

About 5% of the population suffers from this eye disease

Strabismus affects not only children, however, but also many adults whose main symptom is misaligned visual axes.

The causes of strabismus can be many, but it is usually due to malfunctioning eye muscles that do not allow the eyes to look in the same direction.

This results in an impediment to the orientation of the eyes.

This factor then results in incorrect binocular vision and failure to develop the stereoscopic sense, as the brain is unable to obtain information from the two ocular retinas.

What is strabismus

Specifically, strabismus is defined as a pathology involving incorrect alignment of the eyes.

There are therefore deviations in the horizontal, vertical and torsional axis.

Strabismus thus results from the disease causing different eye movements due to malfunctioning of the eye’s muscular and neuromuscular mechanisms.

This pathology can also be constant over time or intermittent.

Moreover, as anticipated, this disease if detected early and in childhood can be resolved or altered through surgery or special therapy.

In adults, on the other hand, this pathology can be a symptom of incorrect muscular functioning, which cannot be corrected.

Types of strabismus

There are different types of strabismus, as it can lead to different functional problems.

Impaired vision is in fact one of the most common symptoms related to strabismus, of different types.

The classification of this pathology can change depending on various factors, such as the causes or the direction of the eyes.

Among the most common types of strabismus are:

Convergent, divergent or vertical strabismus. The first is also called exotropia and is when one or both eyes are turned inwards. The second is also called Exotropia and refers to when the eye looks outwards. If, on the other hand, the eye is looking upwards or downwards, it is referred to as vertical strabismus, the former being Hypertropia and the latter Hypotropia.
Strabismus can also be classified according to the functioning of the eye muscles. Most of these disorders are in fact caused by a malfunction of the eye muscle, in which case it is called paralytic.

It is often due to a muscular injury that can be inflammatory, nervous or traumatic. However, there are also different forms of strabismus in which, when analysed individually, the eye muscles are functional, but external factors, such as nerves, can lead to strabismus.

Another division of strabismus is between tonic, accommodative or mixed.

This classification is based on the relationship between eye convergence and accommodation.

The pathogenesis is linked to medium to high hypermetropia, so that the subject must accommodate not only physiologically for near vision, but also pathologically for far vision, evoking convergence even in far fixation, thus generating the deviation: it is therefore called accommodative strabismus.

Tonic strabismus is when convergence is increased due to an innervational, muscular or orbital defect.

In mixed strabismus both factors lead to strabismus.

Symptoms

Among the symptoms of strabismus, the most common is certainly that of eye deviation.

The symptoms of strabismus, however, are not only related to the direction of the eyes, but vision problems or pain can also occur.

One of the most common symptoms among adults and children is poor depth perception (failure to develop or loss of stereopsis), but also reduced vision.

Especially in adults, strabismus can then lead to headaches, blurred, double and heavy vision and eye fatigue.

For children, on the other hand, one of the already common symptoms is minimised double vision, which leads to unnatural facial movements.

Young children in particular tend to tilt their face and lift their chin in an attempt to see better.

Among the complications of strabismus, and thus often among the post-diagnosis symptoms, there can also be amblyopia, i.e. the phenomenon of lazy eye, as well as reduced motor skills and in children a delay in speaking or walking, generally a delay in development.

Causes of strabismus

The causes of strabismus can be varied, but there are three factors to consider when defining this disease: the cranial nerves, the eye muscles and the higher brain centres.

One of the reasons why strabismus occurs, especially at a young age, is because of vision defects.

Difficulty in focusing or refractive errors such as myopia, hypermetropia or astigmatism can lead a child to deviate the eye.

In the search for a way to see better, the eye may tend inwards or outwards in an attempt to focus.

This movement is not voluntary, but it is the brain that sends impulses to the eyes to avoid double vision.

Among the already widespread causes of strabismus in children is the phenomenon of lazy eye.

In the case of amblyopia in parents or siblings, it is indeed very likely that the child will also have this disease.

Strabismus is then often combined with other diseases such as Down syndrome or cerebral palsy.

These diseases can in fact affect different areas of the body, which determine muscle function and coordination.

It is not uncommon that the causes of squinting also include trauma or neurological problems, which cause further damage to the eye muscles or nerves.

Other eye diseases, such as cataracts, may also be among the causes of strabismus, but premature birth, an oncological condition, diabetes or Graves’ disease may also influence its occurrence.

Diagnosis

For a correct diagnosis of strabismus, it is essential to start with a general eye examination.

During this examination, more specific tests may be requested to assess the severity of the squint and possible treatments.

During an initial examination, the doctor may also ask for the patient’s and family’s medical history, such as cases of strabismus in close relatives, possible medication intake and other pathologies.

Among the tests that are then requested is the visual acuity test, i.e. the eye examination during which the abilities of both eyes are tested.

This test usually consists of recognising letters and numbers on an illuminated panel at a certain distance from the patient.

The examination also includes an orthoptic assessment with a complete eye motility study and various motor and sensory diagnostic tests.

A refractive test to investigate whether there is an underlying refractive error is also fundamental.

Treatments and cures

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As mentioned above, the time at which the diagnosis of strabismus is made can be crucial for eventual treatment.

The earlier this disease is detected, the more likely it will be to choose between several treatment options.

In particular, treatments for childhood strabismus aim to restore the correct development of binocular vision, the sense of depth of field (stereopsis) and align the eyes.

Among the most common treatments for strabismus are:

the use of prescription glasses to eliminate refractive errors, in order to correct myopia, astigmatism and hypermetropia, for example;
the practice of specific eye exercises, which train the eye muscles and help the brain interpret eye impulses;
the injection of botulinum toxin into the muscles in order to reduce the misaligned movement of the eye. This injection weakens the eye, which then naturally sets itself in the correct direction. This type of treatment can become permanent or require further sessions and therapy depending on the severity of the squint.

Strabismus and surgery

In many cases, the most correct and effective treatment indication for strabismus is surgery, which is based on a small incision of the conjunctiva to operate on the eye muscles.

During the operation they are detached from the eye wall and then repositioned correctly in order to weaken or increase their action according to the pre-existing deviation.

General anaesthesia is usually necessary in paediatric patients, however it is possible for adults to perform the operation under local anaesthesia so that the patient is awake to be able to examine the alignment of the eyeball during the operation.

Like any surgery, it is not without risk of infection or organ function, and sometimes there may be irritation and pain in the post-operative period.

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