The pupillary light reflex pathway

Abstract

The anatomy of the human pupillary light reflex (PLR) pathway is a matter of debate. The aim of this study was twofold: namely, to investigate the association of a relative afferent pupillary defect (RAPD) in acquired suprageniculate lesions with the location and extent of the cerebral lesions. Further, we suggest a new strategy of lesion analysis by combining established techniques with the stereotaxic probabilistic cytoarchitectonic atlas developed by the Jülich group. Twenty-three patients with homonymous visual field defects participated in this study. The RAPD was quantified clinically by two independent examiners with graded neutral density filters (swinging flashlight test). Using MRI in each individual, cerebral regions commonly affected in patients with a RAPD but spared in patients without a RAPD were determined and subsequently assessed by using cytoarchitectonic probabilistic maps. A RAPD was present in 10/23 patients. Comparison of patients showing a RAPD vs those not showing a RAPD revealed that a region including the course of the optic radiation at its early beginning in the temporal white matter is commonly associated with a RAPD. It was demonstrated that the pupillary light reflex (PLR) depends on the input of suprageniculate neurons, thus supporting the involvement of a cortical pathway also. The site of integration of cortical signals in relation to the PLR into the pupillomotor pathway may be located suprageniculately in the vicinity of the lateral geniculate nucleus. Moreover, the suggested combination of established lesion analysis techniques with the probabilistic cytoarchitectonic atlas turned out to be a very helpful amelioration of stroke data analyses.