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The swinging-flashlight test is used to help a practitioner decide whether reduced vision is due to ocular disease.
For an adequate test, vision must not be entirely lost. In dim room light, note the size of the pupils. After asking the patient to gaze into the distance, swing the beam of a penlight back and forth from one pupil to the other, each time concentrating on the pupillary size and reaction in the eye that is lit.
- Normally, each illuminated eye looks or promptly becomes constricted. The opposite eye also constricts consensually.
- When ocular disease, such as cataract, impairs vision, the pupils respond normally.
- When the optic nerve is damaged, the sensory (afferent) stimulus sent to the midbrain is reduced. The pupil, responding less vigorously, dilates from its prior constricted state. This response is an afferent pupillary defect (Marcus Gunn Pupil). the opposite eye responds consensually.
- Bickley L.S. 2003. Bates' guide to physical examination and history taking. 8th ed. Lippincott Williams and Wilkins, New York. pp. 169.
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