Strabismus - What is Strabismus?

Strabismus is a condition in which the eyes are not properly aligned with each other.

It typically involves a lack of coordination between the extraocular muscles that prevents bringing the gaze of each eye to the same point in space and preventing proper binocular vision, which may adversely affect depth perception.

Strabismus can be either a disorder of the brain in coordinating the eyes, or of one or more of the relevant muscles' power or direction of motion.

Difficult strabismus problems are usually co-managed between orthoptists and ophthalmologists.

Paralytic strabismus

Forms of paralytic strabismus include

• Third
• Fourth
  • Congenital fourth nerve palsy
  • Sixth
  • Total (external) ophthalmoplegia
  • Progressive external ophthalmoplegia
  • Other
    • Kearns-Sayre syndrome

Other strabismus

Other forms of strabismus include:

• Convergent concomitant/Divergent concomitant
  • Esotropia
  • Exotropia
  • Vertical strabismus
    • Hypertropia
    • Hypotropia
    • Other and unspecified heterotropia
      • Microtropia
      • Monofixation syndrome
      • Heterophoria
        • Esophoria
        • Exophoria
        • Mechanical strabismus
          • Brown's sheath syndrome
          • Other
            • Duane syndrome

Strabismus can be an indication that a cranial nerve has a lesion. Particularly Cranial Nerve III (Occulomotor), Cranial Nerve IV (Trochlear) or Cranial Nerve VI (Abducens).

A strabismus caused by a lesion in either of these nerves results in the lack of innervation to eye muscles and results in a change of eye position.

A strabismus may be a sign of increased intracranial pressure, as CN VI is particularly vulnerable to damage from brain swelling, as it runs between the clivus and brain stem.

More commonly however, squints are termed concominant (i.e. non paralytic).

This means the squint is not caused by a lesion reducing innervation. The squint in this example, is caused by a refractive error in one or both eyes.

This refractive error causes poor vision in one eye and so stops the brain from being able to use both eyes together.

Further Reading

• Strabismus Symptoms
• Strabismus Diagnosis
• Strabismus Treatment

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