The reflex describes the finding of pupillary constriction in darkness or as part of closing eyelids when going to sleep. Westphal–Piltz Reflex was noted by Von Graefe, Westphal and Piltz at different times. Dilation lag detection using infrared videography is the most sensitive diagnostic test for Horner syndrome. Another method of testing for dilation lag is to take flash photographs at 5 seconds and 15 seconds to compare the difference in anisocoria a greater than 0.4 mm difference in anisocoria between 5 seconds and 15 seconds indicates a positive test. Normal pupils return to their widest size in 12-15 seconds however, a pupil with a dilation lag may take up to 25 seconds to return to maximal size. Dilation lag can be tested by observing both pupils in dim light after a bright room light has been turned off. It is described as greater anisocoria 5 seconds after light is removed from the eye compared to 15 seconds after light is removed. Ophthalmologic considerations: Dilation lag may occur in patients with a defect in the sympathetic innervation of the pupil, such as in Horner syndrome. The sympathetic preganglionic neurons in the lateral horn segments send fibers to end on the sympathetic neurons in the superior cervical ganglion, which sends sympathetic postganglionic axons via the long ciliary nerve to the iris dilator muscle.

Pathway: In response to dark, the retina and optic tract fibers send signals to neurons in the hypothalamus, which then descend on the spinal cord lateral horn segments T1-T3. Pupillary escape can occur on the side of a diseased optic nerve or retina, most often in patients with a central field defect.Ī Horner syndrome pupil will show dilation lag “Pupillary escape” is an abnormal pupillary response to a bright light, in which the pupil initially constricts to light and then slowly redilates to its original size. A transient RAPD can occur secondary to local anesthesia. An RAPD can occur due to downstream lesions in the pupillary light reflex pathway (such as in the optic tract or pretectal nuclei). Alternatively, if the reactive pupil constricts more with the consensual response than with the direct response, then the RAPD is in the reactive pupil. If the reactive pupil constricts more with the direct response than with the consensual response, then the RAPD is in the unreactive pupil. Direct and consensual responses should be compared in the reactive pupil. Detection of an RAPD requires two eyes but only one functioning pupil if the second pupil is unable to constrict, such as due to a third nerve palsy, a “reverse RAPD” test can be performed using the swinging flashlight test. When the examiner swings the light to the unaffected eye, both pupils constrict. In patients with an RAPD, when light is shined in the affected eye, there will be dilation of both pupils due to an abnormal afferent arm. Ophthalmologic considerations: Testing of the pupillary light reflex is useful to identify a relative afferent pupillary defect (RAPD) due to asymmetric afferent output from a lesion anywhere along the afferent pupillary pathway as described above. Due to innervation of the bilateral E-W nuclei, a direct and consensual pupillary response is produced. From the E-W nucleus, efferent pupillary parasympathetic preganglionic fibers travel on the oculomotor nerve to synapse in the ciliary ganglion, which sends parasympathetic postganglionic axons in the short ciliary nerve to innervate the iris sphincter smooth muscle via M3 muscarinic receptors. Pathway: Afferent pupillary fibers start at the retinal ganglion cell layer and then travel through the optic nerve, optic chiasm, and optic tract, join the brachium of the superior colliculus, and travel to the pretectal area of the midbrain, which sends fibers bilaterally to the efferent Edinger-Westphal nuclei of the oculomotor complex. Pupillary constriction occurs via innervation of the iris sphincter muscle, which is controlled by the parasympathetic system. The pupillary light reflex is an autonomic reflex that constricts the pupil in response to light, thereby adjusting the amount of light that reaches the retina.

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