The study is designed to evaluate the ability of pattern electroretinogram (PERG) and multifocal pattern electroretinogram (mfPERG) to measure and identify the pattern of band atrophy of the optic nerve in patients with long standing chiasmal lesions. The hypothesis is that these electrophysiological tests were able to identify this such pattern. The idea is to investigate the ability of the these electrophysiological technics in detecting the neural loss from chiasmal compression and to evaluate the ability of PERG and mfPERG parameters to differentiate between eyes with band atrophy of the optic nerve and healthy eyes.