To tell the difference between strabismus and pseudostrabismus, look at a flash photo when the child is looking at the camera and note the position of the light reflection.
If both eyes are properly aligned, the light reflection will be in the center of each pupil, or displaced slightly toward the nose in each eye. If the child has true strabismus and the eyes are not aligned properly, the reflection will appear in a different location in one eye.
Because the light is not affected by the width of the nose or folds of the eyelid skin, a child with pseudostrabismus will have a normal reflection. Parents of a child with strabismus may first notice an abnormal light reflection in flash photos of the child.