Strabismus

The word strabismus comes from the Greek word "Strabismos", whose literal meaning in English is “squint” (to slightly close the eyelids), while in everyday use it refers to a person whose eyes are not aligned.

Strabismus stems from disorders of binocular vision (vision with both eyes) or from disorders of the neuromuscular control of the movement of the eyes themselves (control of the ocular muscles).

Basic concepts in strabismus

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Orthophoria vs Orthotropia

This is a state in which the eyes are perfectly aligned, an uncommon finding in the population. Most of us have a small degree of heterophoria. Therefore, it is customary to label someone with straight eyes under binocular conditions (using both eyes open) as orthotropia (without manifest strabismus).

Heterophoria vs Heterotropia

Heterophoria (latent strabismus) is a state in which, when there is binocular vision, fusion (the union) — or our attempt to unite the two images that reach the brain — succeeds in overcoming the latent strabismus and aligning the eyes.

In contrast, heterotropia (manifest strabismus) is a state in which the fusion mechanism does not succeed in fully aligning the eyes, which leads to manifest strabismus.

Esotropia

The eye is rotated such that the cornea of the eye is turned inward, in a manifest way, toward the nose.

Esophoria

The eye is rotated such that the cornea of the eye is turned inward, in a latent way, toward the nose (under binocular conditions there is no expression of the strabismus).

Exotropia

The eye is rotated such that the cornea of the eye is turned outward, in a manifest way, toward the temple.

Exophoria

The eye is rotated such that the cornea of the eye is turned outward, in a latent way, toward the temple (under binocular conditions there is no expression of the strabismus).

Hypertropia

The eye is rotated such that the cornea of the eye is turned upward, in a manifest way.

Hyperphoria

The eye is rotated such that the cornea of the eye is turned upward, in a latent way (under binocular conditions there is no expression of the strabismus).

Hypotropia

The eye is rotated such that the cornea of the eye is turned downward, in a manifest way.

Hypophoria

The eye is rotated such that the cornea of the eye is turned downward, in a latent way (under binocular conditions there is no expression of the strabismus).

Incyclotropia

The eye is rotated such that the upper pole of the eye is turned inward, in a manifest way.

Incyclophoria

The eye is rotated such that the upper pole of the eye is turned inward, in a latent way (under binocular conditions there is no expression of the strabismus).

Excyclotropia

The eye is rotated such that the upper pole of the eye is turned outward, in a manifest way.

Excyclophoria

The eye is rotated such that the upper pole of the eye is turned outward, in a latent way (under binocular conditions there is no expression of the strabismus).

Congenital strabismus or infantile strabismus

When the strabismus appears up to the age of 6 months, it is customary to call it congenital strabismus or infantile strabismus.

Acquired strabismus

When the strabismus appears after the age of 6 months, it is customary to call it acquired strabismus.