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Pupil Light

REFLEX FITNESS

CHECK

Making Contact

By Shirley Ha, BSc. (Hons), OD, FCOVD

he neurological process of regulating pupil size in varying light levels
is known as the pupil light reflex (PLR). It is invaluable for clinicians to
understand the balance between the parasympathetic and sympathetic
pathways in the autonomic nervous system (ANS) and assess neurological
Tfunction, such as Horner’s syndrome, as well as retinal and optic nerve
head disorders, including glaucoma.
The PRL is more complex than it seems. to assess the pupil dynamics of each eye.

It lacks linearity because the size and These are then compared to determine

function of the pupil are modulated by if there is asymmetry in pupil size and
higher cortical centres responsible for shape, and to identify a relative afferent
attention, accommodation and emotion. It pupillary defect (RAPD).
is also modulated by the interaction with The discovery of the melanopsin containing
the superior colliculus, pretectal olivary intrinsically photosensitive retinal ganglion
nucleus and the locus coruleus, with inputs cells (ipRGCs) in 2000 added new
from the ANS. elements to pupillary light responses and

Conventionally, the standard examination pupillometry research. Recently, both the
is usually done “subjectively” by a clinician sustained pupillary constriction, which is
using a trans-illuminator or a penlight intrinsically driven by the ipRGCs, and

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