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The pupillary light reflex (PLR) is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retinal ganglion cells of the eye, thereby assisting in adaptation to various levels of lightness/darkness.he pupillary reflex pathway begins with the photosensitive retinal ganglion cells, which convey information to the optic nerve (via the optic disc). The optic nerve connects to the pretectal nucleus of the upper midbrain, bypassing the lateral geniculate nucleus and the primary visual cortex.
Some reflexes, such as the muscle stretch reflex, are semi-quantitatively graded. This is also true for responses such as the pupillary light reflex, where the speed of reaction may indicate a sluggish response. On the other hand, many reflexes are simply noted as present or absent.ormal muscle stretch reflexes result in contraction only of the muscle whose tendon is stretched and the agonist muscles (i.e., muscles that have the same action). There is also inhibition of antagonist muscles. Reflexes are graded at the bedside in a semi-quantitative manner.