see also: [[Mydriasis]], [[pupil exam]] In the [swinging flashlight test](https://en.wikipedia.org/wiki/Swinging_flashlight_test "Swinging flashlight test"), a light is alternately shone into the left and right eyes. > An RAPD may be partial or complete and due to inhibition of light transmission to the retina because of vitreous haemorrhage, loss of some or all of the retinal surface for light contact because of ischaemia or detachment, or the presence of lesions affecting the *pre-chiasmal optic nerve (CN II)* (e.g., optic neuritis) A **normal response** would be equal constriction of both pupils, regardless of which eye the light is directed at. This indicates an intact direct and consensual [pupillary light reflex](https://en.wikipedia.org/wiki/Pupillary_light_reflex "Pupillary light reflex"). When the test is performed in an eye with an **afferent pupillary defect**: - light directed in the affected eye will cause only mild constriction of both pupils (due to decreased response to light from the afferent defect) - light in the unaffected eye will cause a normal constriction of both pupils (due to an intact efferent path, and an intact consensual pupillary reflex). Thus, ==light shone in the affected eye will produce less pupillary constriction than light shone in the unaffected eye== # causes > not all these conditions necessarily have a RAPD if the condition is present - [[Multiple Sclerosis]] with acute flare/optic neuritis - severe retinal disease - [[Glaucoma]] - orbital compartment syndrome needing [[Lateral canthotomy]] - [[eye trauma#retrobulbar haematoma]] - [[Eye infections#Periorbital and orbital cellulitis|orbital cellulitis]] - [[Central retinal artery occlusion|CRAO]] - [[Central retinal vein occlusion|CRVO]] - [[Retinal detachment]] - Stroke/ TIA - [[Giant Cell Arteritis|GCA]]