Ophthalmic Instruments and Diagnostic Tests

The cover test is done to confirm the presence of a manifest squint. The patient is asked to look at the fixation target (a flashlight should never be used as a fixation target because it fails to control accommodation—an accommodative fixation target held at 33 cm is used for near and the Snellen 6/9 visual acuity symbol is used for distance fixation). The apparently fixating eye is then covered and the behavior of the uncovered eye is noted. Each eye is tested in turn for near (33 cm) and distance (6 m). It is performed in all nine positions of gaze. Head posture should be straight. The test is performed with and without eyeglasses. In the presence of squint, the uncovered eye moves to take up fixation. If there is no movement of the uncovered eye, that eye is then covered and the other eye observed. No movement of either eye is seen in pseudosquint.