Third International Visual Field Symposium - Imaging and Perimetry ...

ut only thinning of the arcuate bundles (Fig. 5). Smaller degrees of dam-
age, with relative visual field defects, are very difficult to detect ophthal-
moscopically.
Tract lesions are generally impossible to distinguish from lateral geni-
culate lesions from the appearance of the fundus or the visual field defects
(Hoyt 1975, Hoyt & Kommerell 1973). Homonymous sectorial defects,
with corresponding sectorial optic atrophy, constitute an exception indica-
tive of partial lateral geniculate damage (Fri.&, Holmegaard & Rosencrantz
1978).
TIME COURSE OF OPTIC ATROPHY
A cross-sectional lesion of the optic nerve results in loss of axons about six
weeks after the lesion (Lundstrom & Frisen 1975). Experimental studies
show that degeneration does not occur step by step along the axon, but all
of the axons anterior to the lesion degenerates at the same time (Anderson
1973). This observation suggests that the time course of fundus changes
with anterior visual pathway lesions should be independent of the actual site
of the lesion. The delay must be kept in mind when evaluating the retinal
nerve fiber layer in patients with acute impairment of vision: the fiber
bundles usually appear perfectly normal for several weeks following the
debut of visual loss. Disc pallor is a still more protracted sign. The same
Fig. 5. Schematic representation of typical nerve fiber layer abnormalities due to a
left retro-chiasmatic lesion, with right homonymous hemianopia.
13