Ocular deviation

What is strabismus?

Strabismus is a misalignment of the eyes; hence they do not look at the same object at the same time.

This misalignment can be permanent or temporary and the eyes can point in any direction: inward, outward, upward or downward. In children, it must be treated in early stages in order to avoid amblyopia or lazy eye, in which the brain ignores the image which the deviated eye sends, resulting in irreversible visual impairment of this eye.

Normal eyes without strabismus

What causes it?

It can be caused by any of the following:

  • Genetic inheritance.
  • Lack of muscle coordination, debilitated muscles or abnormal nervous impulses sent to eye muscles.
  • Eye muscles’ disorders due to impaired vision, infections, tumours or traumatisms.
  • Thyroid gland disorders.

Other disorders which are linked to strabismus are:

  • Apert syndrome.
  • Cerebral palsy.
  • Congenital rubella.
  • Hemangioma around the eye.
  • Incontinentia pigmenti (pigment incontinence) syndrome.
  • Noonan syndrome.
  • Prader-Willi syndrome.
  • Retinopathy of prematurity.

Strabismus classification

  1. According to direction of the deviation.

    Esotropia - Convergent Strabismus
    Exotropia - Divergent Strabismus

  2. According to regularity.

    • Intermittent Strabismus - It occurs only under certain circumstances (illness, nervousness, fatigue, stress), when looking at certain directions, or at certain distances (near or far away).
    • Constant Strabismus - The eye turns all of the time; it is persistent.

  3. According to preference for one eye over the other.

    • Alternating Strabismus - Both eyes can act as the fixating eye. The brain ignores the image received from the deviated eye, but the alternation in the deviation allows a similar visual development in both eyes and a correct visual acuity.
    • Monocular Strabismus - The fixating eye is always the same one, while the other one is constantly deviated. This can lead to amblyopia in the deviated eye if strabismus takes place during the period of vision development (before the age of 8).


After a rigorous examination to determine the cause and type of the existing strabismus, the ophthalmologist will decide on the most adequate treatment.

The aim of strabismus treatment depends on the age of the patient. During childhood, the aim is to preserve vision in the deviated eye in order to achieve binocular vision. During adulthood, the goal of strabismus treatment is to realign both eyes for esthetical purposes.

Optical correction (glasses or contact lenses) or refractive surgery can be used to correct any existing refractive errors (myopia, hyperopia, astigmatism). Generally, once the refractive error is corrected, strabismus disappears.

Children with lazy eye (amblyopia) as a consequence of strabismus, have to follow a specific treatment to regain vision in the affected eye, by covering the good eye using an eye patch in order to penalize it so that the lazy eye is forced to work too.

Diagnosing and treating strabismus before the age of 5 is hugely important to prevent amblyopia.

Dr. Lorenzo Vallés | Strabismus Expert

Surgical treatments are only required if strabismus persists after correcting refractive errors and amblyopia.

Surgical treatments

Surgical procedures to treat strabismus consist in weakening or strengthening the relative strengths of the extraocular muscles depending on the type and severity of strabismus.

It is an outpatient procedure which is carried out using topical anaesthesia in adults. In children, general anaesthesia must be used.


It is quick and easy
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