Strabismus is the medical term for any eye misalignment. Pseudostrabismus refers to a false appearance of strabismus caused by an optical illusion. [See figure 1].
Fig. 1: Most often in pseudostrabismus, the eye(s) have the false appearance of turning inward.
Why do some children's eyes look crossed?
The skin folds at the inner corner of the eyelids are called epicanthal folds and can be broad in some babies. This is often associated with a broad flat nasal bridge. These features contribute to a crossed eye appearance since there is less sclera (white surface of the eye) exposed nasally compared to the temporal side. This is especially noticeable in pictures and when the child looks to the side. When the child looks to either side it creates the optical illusion that the eye turning inward appears to be much further into the nose than it should be.
How does a doctor determine if a child has true strabismus or pseudostrabismus?
The Eye MD has several tests to determine if a real strabismus is present. A simple test is to shine a light onto both eyes and determine where the light reflects on the surface of the eyes. The light should fall on the center of each pupil at the same time. If a true strabismus is present the light reflexes do not fall on the same position of each eye. A more detailed test that is more sensitive to tiny deviations is called a cover test. The eyes are alternately covered while the fixation of each eye is monitored. If either eye has to move to fixate a strabismus is present. A complete eye exam should also be performed to rule out potential causes of true strabismus such as unequal vision (amblyopia) or high refractive error (hyperopia/far-sightedness).
Positive Angle Kappa
Another form of pseudostrabismus is known as a Positive Angle Kappa. This occurs when the light reflection is not centered over the pupil when the eye is looking at the light. Instead the light reflection is nasal to the center. This gives the appearance that the eye is deviated outwards. There is no movement with the cover test. This is another example of pseudostrabismus.
Why is it important to differentiate pseudostrabismus from true strabismus?
True strabismus in a child can lead to permanent vision loss and is best treated early. If a child is suspected of having strabismus, an Eye MD evaluation is important. It may be difficult for a pediatrician to differentiate between true strabismus and pseudostrabismus.
What is the treatment of pseudostrabismus?
Pseudostrabismus does not require treatment and the appearance tends to improve with time as facial features mature. Asian children may retain a broad nasal bridge into adulthood. It is important to remember that a baby with pseudostrabismus might develop a real strabismus later in life.