EARLY IMPAIRMENT OF FOVEAL MAGNOCELLULAR AND PARVOCELLULAR PATHWAYS IN JUXTA CHIASMAL TUMORS

Foveal pathway visual function was assessed in 11 patients having tumo nrs extending into the suprasellar region but without evidence of visu al impairment as assessed by visual acuity and Bjerrum screen campimet ry. Psychophysical and routine visual evoked potential (VEP) measureme nts were obtained from the eye ipsilateral to the maximal suprasellar extension. The sensitivity of luminance and chromatic pathways was ass essed psychophysically by measuring increment thresholds for white and red flashes of light presented on a white adapting field. Temporal se nsitivity was assessed psychophysically by measuring threshold modulat ion sensitivity for sinusoidally modulating stimuli (de Lange attenuat ion characteristic). The patient group showed approximately equal sign ificant psychophysical losses in chromatic, luminance and temporal sen sitivities relative to normal controls. Midline VEP P100 latencies of the patient group did not significantly differ from those of the norma l control group, ft is concluded that tumours extending into the supra sellar region can cause foveal pathway dysfunction affecting both magn o- and parvocellular pathways, even in the presence of normal visual a cuity and fields suggesting a more widespread and insidious abnormalit y of the visual pathways in this condition than previously thought. (C ) 1997 Elsevier Science Ltd.