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Strabismus


Crossed eyes, or strabismus,is a condition when both eyes do not align with each other at same time when looking at same object. It usually occurs in people who have poor eye muscle control or are very farsighted, have problems in the brain, trauma, or infections. The eye which is focused on an object can alternate. The condition may be present occasionally or constantly.

Strabismus can occur due to muscle dysfunction. Six muscles are attach to each eye to control its movement. These muscles receives signals from brain that directs the movement. Normally, both eyes works together so they both points at the same place. When eyes are misaligned, brain receives two different images creating double vision. Over the time brain will learn to ignore images from turned eye.

Strabismus is classified by the direction the eye turns:

  • Inward turning is called esotropia
  • Outward turning is called exotropia
  • Upward turning is called hypertropia
  • Downward turning is called hypotropia.

Other classifications of strabismus include:
  • The frequency with which it occurs-either constant or intermittent
  • Whether it always involves the same eye-unilateral
  • If the turning eye is sometimes the right eye and other times the left eye-alternating.

The eye turning may occur all the time or may appear only when the person is tired, ill, or has done a lot of reading or close work. In some cases, the same eye may turn each time and in other cases, the eyes may alternate turning. It may occur when a person may look in any directions (comitant) or varies by direction (incomitant).

Strabismus can develop to anyone, infants or adults but it usually develops among infants and younger children, most often by age 3. Some infants may have misaligned eyes, which are actually aiming at same object. This is a condition called pseudostrabismus or false strabismus. This can be due to extra skin in the inner corner of eye or wide bridge of the nose; which usually gets corrected as the baby’s face begin to grow.

Risk factors for developing strabismus include:

Premature birth, Down syndrome, Loeys-Dietz syndrome, cerebral palsy, or who have suffered a stroke or head injury are at a higher risk for developing strabismus. The risk is increased among those with a family history of the condition.

How is Strabismus diagnosed?

Strabismus can be diagnosed through comprehensive eye exam carried out by optometrist, giving special emphasis on how the eyes focus and move. This may include:

  • Visual Acuity - To assess how much vision is being affected, an optometrist will measure visual acuity by asking patience to read letters on charts that are at near and at distance. There are other methods for measuring vision in infants or young children who can not speak or comprehend the visual acuity test.

  • Refraction - A phoropter is used by an optometrist to conduct refraction error. In this, the optometrist places a series of lenses in front of your eyes and measure how they focus light using a hand held lighted instrument called a retinoscope. This test is to determine appropriate lenses power required to compensate any refractive error (nearsightedness, farsightedness or astigmatism). An optometrist may also use automated instrument that evaluates the refractive power of eye without patient needing to answer any question.

  • Alignment and focusing testing - You can see single clear image of what you are viewing only when both the eyes effectively change focus, move and work in unison. An optometrist will carry on this test to identify problem that keep your eyes from focusing effectively or make it difficult to use both eyes together.

  • Examination of eye health - In this test, an optometrist will observe internal & external structure of your eyes to identify any eye disease causing strabismus. This testing will determine how the eyes respond under normal seeing conditions. An optometrist may use eye drops for infants or young children who can not respond to test verbally.Using the information obtained from these tests, along with results of other tests, your optometrist can determine if you have strabismus. Once testing is complete, your optometrist can discuss treatment options.

How is Strabismus treated?

It's believed that child with Strabismus will outgrow the condition, which is not true. In fact, Strabismus or Turned eye if untreated, can permanently reduce vision in one eye. This condition is also called amblyopia or lazy eye. There are many treatment options for improving eye alignment and coordination which includes eye glasses or contact lenses. This may be the only treatment required for some patients while other may need prism lenses, vision therapy or eye muscle surgery.