The most useful piece of evidence for localization of the site of compression is that provided by examination of the visual fields. (4). Although the fields must always be recorded for future comparison, confrontation with a small red object can provide invaluable immediate evidence of hemianopsias (bitemporal or homonymous) and scotomata.
In examining the fields by confrontation, it is important to test both the peripheral and the central areas. The latter is done best by holding a small red object halfway between the patient's and the examiner's eyes and asking the patient to compare the quality of the color when the object is moved quickly from a few degrees within the nasal field to a few degrees into the nasal field. Desaturation of the color within the temporal field is an early sign of chiasmal compression.
Fields are now most commonly plotted using the Humphrey automated perimeter system. Regardless of where it is performed, the automation ensures a reliable uniformity of response that is easily compared regardless of where the original was performed, with the follow-up from one's own unit. Goldman fields may remain the gold standard in difficult cases, and in experienced hands the tangent screen is invaluable for revealing the details of field loss. Comparison of fields over time is facilitated by using the same symbols and colors on successive occasions—an obvious point surprisingly often forgotten. Who checks that the Humphrey visual field test is the same stimulus (our unit uses the Goldman I4e)? Failure to compare like with like is a known cause of urgent referral to our pituitary clinic.
Bitemporal hemianopia is one of the most common findings with pituitary tumors and indicates chiasmal compression (Fig. 2). The completeness of the hemianopia varies and depends on the size of the tumor and position of the chiasm. When the latter is markedly postfixed, quite a large suprasellar extension of a tumor may produce minimal, if any, loss.
The field loss often begins unilaterally, when the intracranial optic nerve is compressed close to its junction with the chiasm. Early involvement of the
Fig. 2. (opposite page) (A) Goldmann field assessment. Typical bitemporal hemianopia resulting from chiasmal compression. (B) Humphrey field assessment. Only the full threshold picture is shown, illustrating a dense left temporal field loss and a lesser degree of upper right quadrantic field loss.
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