Nystagmus is a necessary eye movement for the student with macular damage. Strabismus has more serious implications. Alternating or intermittent strabismus is a better situation because it means that amblyopia has not yet settled in, but it can lead to confusion and even dangerous mobility circumstances when the eyes decide suddenly to switch dominance. At the same time, a confused classroom teacher will report that the same student is moving in and out doors and around objects one minute and acting blind the next. This paradox is usually about the extraocular muscle system.
Doctors examine children in a clinical setting.
They control lighting, they control distances, and most importantly they keep the patients stationary, in a chair. They often get little information from multiply impaired students, despite their best efforts. They may get no indication under these clinical conditions that the child can see. In a classroom, while moving, the peripheral vision system, even with a dysfunctional oculomotor system, can at times signal the presence of objects or the location of doorways or landmarks. These kids have functional vision, they just can't control the eye muscles often enough to provide consistent, reliable vision.