Strabismus is a visual problem in which the eyes are not properly aligned and look in different directions (comes from a Greek word meaning “eyes looking at an angle”). This ophthalmological condition is characterised by the deviation of one or both eyes from the central axis. It may seem like a purely aesthetic issue – but it’s not. Because the eyes do not act simultaneously, the one who looks straight becomes dominant. His visual acuity remains normal because his eye and its connection to the region responsible for vision in the brain is functioning as it should.

In contrast, the eye that has problems with alignment or is completely deviated does not fixate visual stimuli, the projection of the image on the retina is extramacular (temporal or nasal), so its connection with the brain is not formed correctly. Thus develops
amblyopia
– physiological problem.

Amblyopia
occurs in 40% of children with strabismus and is the leading cause of vision loss in one eye for the 20-70 year old population.

Now that we have clarified what strabismus means, let’s look at the most common types of strabismus

For each form of strabismus are typical symptoms of deviation in one direction. Thus, when one eye looks straight ahead towards the object being fixed, the other eye is misaligned inwards (esotropia or “crossed eyes”), outwards towards the ear (exotropia or divergent), upwards (hypertropia) or downwards (hypotropia). The prevalence of strabismus is 2 to 5 percent in the general population, according to the latest studies.

According to current data, esotropia is the most common type of strabismus and occurs in different forms:

• Infantile esotropia or congenital strabismus occurs at birth or develops in the first six months of life. The child often has a family history of strabismus. Although most children with infantile esotropia are perfectly healthy, there is a high incidence of the condition among children with cerebral palsy, hydrocephalus, Down syndrome or Apert-Crouzon syndrome. It is common among low birth weight premature infants and children with parents or siblings who have strabismus. All siblings of a strabismic child should be screened at an early age for strabismus.
• Many infants appear to have strabismus, but most often they have a condition known as pseudostrabismus or false strabismus. They may have an enlarged nasal bridge or an excess of skin at the boundary between the eyes and nose that makes the white sclera of the eyes less visible on the side of the nose, giving the impression that the eyes are looking inwards. As the facial structures mature, the eyes will look normal.
• Accommodative esotropia is the most common form of esotropia occurring in children under 2 years of age or older. In this type of squint, when the child focuses to see an object clearly up close, the eyes turn inward.

Statistics show that fifty percent of all childhood esotropies are either fully or partially accommodative. Non-accomodative esotropia is seen in 10% of all strabismus and is the second most common form of childhood esotropia. Childhood esotropia affects one in 100 to 500 people, which represents 8.1% of esotropia cases. Intermittent esotropia is seen in a percentage of the population and is the most common form of exotropia.

Another form of strabismus frequently encountered is exotropia. Also called divergent strabismus (the deviation of one eye outwards towards the temple), this form of squint is less common. It affects older children or adults and often occurs in patients with myopia or those with later vision loss. It occurs at certain times of the day, especially when the patient is tired or inattentive. This deviation is easily noticeable especially in bright light.

Most common types of strabismus are:

• Congenital divergent strabismus (present at birth)
• Intermittent exotropia
• Sensory exotropia
• Acquired exotropia (most commonly following strabismus surgery)

Transient intermittent divergent squint is usually seen in the first 4-6 weeks of life. It may progress favourably and heal spontaneously in up to 8 weeks, or it may require medical intervention if the form is more severe.

Sensory exotropia occurs when the lower-vision eye struggles to work as a team with the other eye, the weaker eye may have a tendency to move outward, causing sensory exotropia. This type of exotropia can occur in individuals of any age and, because the vision problem is treatable, should be addressed quickly.

Another type of exotropia that is quite rare is congenital divergent strabismus or constant exotropia, present at birth.

Another classification divides the types of squint into intermittent or constant. Intermittent strabismus can occur when the eye muscles are tired – for example, in the evening or during an episode of illness. From time to time, in the first months of life, when the child is exhausted, parents may notice their child’s eyes looking in different directions. These incidents are perfectly normal as the child is still learning to focus their eyes and work together. Most babies outgrow this intermittent squint by 3 months of age.

What treatment solutions exist for different types of squint?

For some types of strabismus surgical treatment is recommended. In most cases, strabismus is cured without surgery if the little patient is taken to an ophthalmologist early. This is only possible with glasses and vision therapy. In many cases, strabismus recurs after surgery. Plus, strabismus surgery only solves the problem of aligning the eye axes, has only aesthetic value and does not improve vision.

This is where visual therapy. How does it work? Visual therapy includes a set of computerized exercises aimed at stimulating the eye and cortex to improve visual acuity, ocular motility, the fusion of images transmitted by the eye to the brain and to develop optimal binocular vision. Exercises are designed in interactive form – friendly and easy to play games. The treatment protocol is structured in stages: therapy sessions at the clinic and then – series of sessions at home. All sessions are monitored by a specialist in visual therapy.

At first, the targets in the games are easy to see, but then, with each progress, they become more complex. Thus, visual information starts to be processed in the brain and the vision of the problem eye and binocular vision improves. A major benefit is that following vision therapy sessions, not only do the eyes begin to work as a team, but also contrast sensitivity, hand-eye coordination improves and the patient begins to better appreciate distances in space.