Distribution of scotoma pattern related to chiasmal lesions with special reference to anterior junction syndrome

Purpose: To evaluate pathogenetic mechanisms and frequency distribution of visual field defects (VFDs) in patients with chiasmal lesions. Secondly, to reconsider the existence of Wilbrand's knee as far as referable to the anterior junction syndrome. Methods: Consecutive visual field records related to chiasmal lesions were retrieved from the Tuebingen Perimetric Database. In all cases, at least one eye was examined with the Tuebingen Automated Perimeter using a standardized grid of 191 static targets within the central 30degrees visual field, and a threshold-related, slightly supraliminal strategy. VFDs were classified according to standard neuro-ophthalmological categories. Results: Results from 153 consecutive patients (65 male, 88 female) were evaluable. The majority (65%) of chiasmal lesions was due to pituitary adenoma, followed by craniopharyngioma (12%), astrocytoma (9%), and meningioma (8%). Vascular lesions in this region occurred rarely (2%). Three per cent of all patients had no final diagnosis. The majority (22%) of scotomas was attributable to involvement of the temporal hemifield in both eyes, with true bitemporal hemianopia being a very rare event (1%). Anterior junction syndrome, characterized by advanced visual field loss affecting the visual field centre in one eye and (possibly subtle) defects respecting the vertical midline in the fellow eye, was the second most frequent classifiable VFD (13%). Homonymous hemianopic VFDs occurred in 11% of all cases. Nine per cent of all patients exhibited monocular VFDs which did not respect the vertical midline, whereas in 3% of the subjects the monocular VFDs did not cross the vertical meridian. Binasal defects and posterior junction syndrome also occurred seldom (<1%). Nineteen per cent of all visual field records of patients with chiasmal lesions had results, which could not be classified unequivocally, and an identical portion was rated normal. Conclusion: In patients with chiasmal lesions, incomplete involvement of the temporal hemifields in both eyes was the most frequent event (22%), followed by anterior junction syndrome (13%). The latter entity at least clinically indicates the proximity of the pre-chiasmal ipsilateral optic nerve and decussating fibres emanating from the inferior nasal hemiretina of the fellow eye. However, this cannot provide conclusive evidence for the existence of anterior Wilbrand's knee.