How robust is the optic chiasm? Perimetric and neuro-imaging correlations

Abstract

Analysis of form and function relationships with tumour-mediated dislocations and deformations of the optic chiasm. Results of magnetic resonance tomography and two forms of quantitative, computerized perimetry were contrasted in 31 patients with pituitary adenomata impinging on the chiasm, prior to treatment. Perimetric abnormalities ranged from none to modest. High-pass Resolution Perimetry (HRP) produced abnormal results in 10 cases and RareBit perimetry (RBP) in 15 cases. Overall, field defects and qualitative stages of deformation and dislocation of the chiasm were well correlated. Among quantitative indices, the best correlations were obtained by a measure of the cranio-caudal position of the chiasm. On average, an elevation of the chiasm by 6 mm will be associated with abnormal visual fields in 50% of the cases. An additional elevation of 5 mm will raise the incidence of field defects to 90%.