- Inward turning is called esotropia
- Outward turning is called exotropia
- Upward turning is called hypertropia
- Downward turning is called hypotropia.
- 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.
What causes strabismus?Strabismus can be caused by problems with the eye muscles, the nerves that transmit information to the muscles, or the control center in the brain that directs eye movements. It can also develop due to other general health conditions or eye injuries. Risk factors for developing strabismus include:
- Family history – individuals with parents or siblings who have strabismus are more likely to develop it.
- Refractive error – people who have a significant amount of uncorrected farsightedness (hyperopia) may develop strabismus because of the additional amount of eye focusing required to keep objects clear.
- Medical conditions – people with conditions such as Down syndrome and cerebral palsy or who have suffered a stroke or head injury are at a higher risk for developing strabismus.
How is strabismus diagnosed?Strabismus is diagnosed through a comprehensive eye exam. Testing for strabismus, with special emphasis on how the eyes focus and move, may include:
- Patient History – A patient history is obtained to determine any symptoms the patient is experiencing or the parent is observing, and to note the presence of any general health problems, medications taken, or environmental factors that may be contributing to the symptoms.
- Visual Acuity – Visual acuity measurements are taken to assess the extent to which vision may be affected. As part of the testing, you will be asked to read letters on distance and near reading charts. This test measures visual acuity, which is written as a fraction such as 20/40. When testing distance vision, the top number is the standard distance at which testing is done, twenty feet. The bottom number is the smallest letter size you were able to read at the twenty foot distance. A person with 20/40 visual acuity would have to get within 20 feet of a letter that should be seen at forty feet in order to see it clearly. “Normal” distance visual acuity is 20/20.
- Refraction – A refraction is conducted to determine the appropriate lens power needed to compensate for any refractive error (nearsightedness, farsightedness, or astigmatism). Using an instrument called a phoropter, your optometrist places a series of lenses in front of your eyes and measures how they focus light using a hand held lighted instrument called a retinoscope. Or the doctor may choose to use an automated instrument that automatically evaluates the refractive power of the eye. The power is then refined by the patient’s responses to determine the lenses that allow the clearest vision.
- Alignment and Focusing Testing – How well your eyes focus, move and work together needs to be assessed. In order to obtain a clear, single image of what is being viewed, the eyes must effectively change focus, move and work in unison. This testing will look for problems that keep your eyes from focusing effectively or make it difficult to use both eyes together.
- Examination of eye health – The structures of the eye are observed to rule out any eye disease that may be contributing to strabismus. The health of the external and internal parts of the eye will be assessed using various testing procedures.
How is strabismus treated?People with strabismus have several treatment options available to improve eye alignment and coordination. They include:
- eyeglasses or contact lenses
- prism lenses
- vision therapy
- eye muscle surgery