Decompression of the anterior visual pathways can result in a remarkably rapid and complete recovery of vision, provided not too many of the optic nerve fibers have degenerated. The risk of irreversible change is increased by both abrupt compression (as in apoplexy) and by prolonged compression, when severe optic atrophy reflects the severity of the nerve fiber loss. Although this seems remarkably obvious, it is difficult to prove from the various surgical series on postsurgical visual recovery in the literature. Furthermore, it is far from clear how quickly surgical intervention must be performed once chiasmatic compression from a tumor mass has been or should have been demonstrated. When most physicians discover a mass, they clamor to have the mass removed at the next available opportunity by the best possible surgeon, a luxury that in these days of healthcare rationing is not immediately available to every patient. In the protocol established at our hospital, the maximum period of delay should be 6 wk, but even this is far too long in some cases and not ideal. Nevertheless, despite horrific-looking scans, minimal visual loss in some patients often stablizes over many months.
When recoverable, visual fields may start to open in the recovery area immediately after surgery and further open in the following days, which questions the mechanisms of vision recovery after decompression, which have been investigated experimentally (5,6). It is probable that the immediate recovery depends on the reversal of ischemic conduction block in demyelinated, remyelinated and morphologically intact fibers. The slower phase probably depends on progressive remyelination and adaptive synaptic mechanisms to compensate for axonal loss (7). Complete recovery may continue for months, and, in our clinic, improvement after 2 or 3 yr is not unknown. Recovery of vision in the five major surgical series is given in Table 1 (8-12).
Recovery of Vision: Surgical Series Results
Pt No. Recovery and type
Symon, 1979 (10) 101 57% Full/37% partial
Cohen, 1985 (11) 100 Findlay, 1983 (12) 34 Laws, 1977 (8) 62
79% Acuity/74% fields 85% Improved 16.7% Full fields, 69% improved
Craniotomy series with "giant" tumors excepted Best overall data Complex field assesment
Powell, 1995 (9) 67 34% Full/43% partial fields
Unusual incomplete bitemporal bitemporal or binasal defects are occasionally found in asymptomatic individuals being examined for some other purpose, most often in the course of assessment for corrective lenses. Such defects are often associated with anomalously shaped (tilted) or hypoplastic optic discs (Fig. 5), and are of no pathologic significance. If, however, there is any doubt about the cause of such defects, compression of the chiasm must be excluded by appropriate imaging.
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