[Clinical aspects of the abnormal pupillary response; shedding light on pupillary response].

Testing the pupillary response is a quick and valuable diagnostic measure for certain neurological and ophthalmological diseases in patients. The pupillary response can aid in localizing abnormalities in important parts of the visual system and brainstem, provided that the tests are executed and interpreted correctly. When an abnormal pupillary response is found, it is important to differentiate between an afferent problem (eyeball, retina, optical nerve), brain stem pathology, or an efferent problem (parasympathetic fibers of the oculomotor nerve, iris sphincter muscle). We describe the technique of the ophthalmological examination, the normal neurophysiology and the possible abnormal pupil responses in patients with intact and decreased consciousness.