The swinging flashlight test is a clinical examination used to detect a relative afferent pupillary defect (RAPD), which often indicates damage to the optic nerve or retina. It evaluates how the pupils respond to light, particularly when the light is alternated between the two eyes.
1. Normal Response:
Both pupils should constrict when light is shone into either eye (direct response). When the light is moved from one eye to the other, the pupils should equally constrict and then dilate as the light moves.
2. Abnormal Response (RAPD):
In a person with RAPD, when light is directed into the affected eye, the pupil may dilate (called a "relative afferent pupillary defect"), even though light is present. This occurs because the optic nerve of the affected eye is not responding properly to the light stimulus. When the light is moved to the unaffected eye, the pupil will constrict normally.
Clinical Relevance:
RAPD suggests damage to the afferent pathway of one eye, typically the optic nerve or retina. Common causes of RAPD include:
1. Optic neuritis (inflammation of the optic nerve)
2. Glaucoma
3. Retinal diseases
4. Optic neuropathy