Binocular alignment is evaluated with a cover test. The examiner holds a point light source beneath his or her own eyes and observes the light reflec-tions in the patient’s corneas in the near field (40 cm) and at a distance (5 m).The reflections are normally in the center of each pupil. If the corneal reflection is not in the center of the pupil in one eye, then a tropia is present in that eye. Then the examiner covers one eye with a hand or an occluder (Fig. 1.6) and tests whether the uncovered eye makes a compensatory movement. Compen-satory movement of the eye indicates the presence of tropia. However, there will also be a lack of compensatory movement if the eye is blind. The cover test is then repeated with the other eye.
If tropia is present in a newborn with extremely poor vision, the baby will not tolerate the good eye being covered.