Patients with lesions in the neighborhood of the chiasm usually complain first of visual symptoms. The responsibility for diagnosis of these lesions therefore rests primarily upon the ophthalmologist. When one considers that almost one in four brain tumors1 lies in the chiasmal region and that chiasmal lesions often threaten not only the vision in both eyes but life itself, it is apparent that the responsibility is great.
CHARACTERISTICS OF CHIASMAL LESIONS
All of us are aware that a bitemporal hemianopsia is a classic finding in a chiasmal lesion. However, we often forget that this hemianopsia is frequently not present in pure form. It is often masked by overlying variations, and occasionally it is not present at all. There are, nevertheless, certain field findings which are of localizing value in chiasmal lesions. These are as follows:A bitemporal hemianopsia with "steps" along the vertical meridian in either one or both
WENDLAND JP. Some Instructive Manifestations of Chiasmal Disease: One Case of Pituitary Adenoma, One of Optochiasmal Neuritis (Arachnoiditis), and One of Chiasmal Glioma. AMA Arch Ophthalmol. 1955;54(1):13–21. doi:10.1001/archopht.1955.00930020015003
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