Early visual dysfunction in pituitary adenomas. role of the p- and m-pathway

Purpose. Expansive processes impinging on the optic chiasm affect visual acuity and visual field only when they are in a rather advanced stage. However, it is important to detect early visual deficits to monitor the evolution of the disease and establish limits beyond which surgery is necessary Methods. Contrast sensitivity (CS) was measured for stimuli selective [Merigan, 1990; 1991] for the P-pathway (static gratings of 2 c/deg) or the M-pathway (gratings of 0.3 c/deg, counterphased at 10 Hz), presented monocularly in the right or left hemifield. Both the average CS loss and the sensitivity ratio between hemifields (HR) were evaluated. Measurements were done in 14 normal controls and 32 patients with different types of pituitary adenoma. Visual acuity, visual field (Humphrey 30-2) and NMR were also evaluated Results. 1) In the great majority of patients the CS and the HR were clearly altered, whereas both the visual acuity and visual field were normal. 2) CS and HR losses were of different extent for stimuli of the P- or Mparadigm, the former being more frequently altered. 3) In four patients who underwent surgery there was a clear improvement of CS and HR (of different extent for the P- or M- paradigm). 4) CS and HR losses were little correlated with both the size of adenoma and the way the adenoma impinges on the optic chiasm. Conclusions. Measuring the CS and the hemifield sensitivity ratio for stimuli specific for the P- and M-pathway is useful to detect subclinical visual changes in patients with pituitary adenomas and monitor the evolution of the disease. Results are also relevant for a better understanding of segregation of the P- and M- fibers at the level of the optic chiasm.