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

conduction disturbances. Their cause is not known.
Axonal distension has also been described as a feature of optic neuritis,
anterior ischemic optic neuropathy, and constrictive optic neuropathy
(Hoyt 1976, Ito, Ozawa, Suga & Mizuno 1969, Lundstrom 1974). It is also
seen in the early phase of Leber’s acute optic neuropathy, together with
hyperemia of the nerve fiber layer (Smith, Hoyt & Susac 1973). What causes
axonal distension, and later axonal atrophy, in Leber’s disease is as yet
unknown. The same clinical picture with central scotomata and hyperemic
axonal swelling is characteristic also of the acute phase of so-called tobacco-
alcohol amblyopia (unpublished observations).
ATROPHY OF NERVE FIBRES
Damage to axons of the anterior visual pathway somewhere posterior to the
eye may lead to both anterograde and retrograde axonal degeneration (An-
‘derson 1973). Degeneration produces pallor of the optic disc and loss of 1
retinal nerve fibers. A circumscript lesion may produce localized pallor and
localized wasting of nerve fibers. Recent studies suggest that disc pallor
primarily is caused by changes in light transmission and light reflection
properties with loss of nerve fibers (Quigley & Anderson 1977). Pallor is an
indirect sign of loss of nerve fibers. Its poor reliability in diagnosis requires
no comment here. The essential hallmark of optic atrophy, viz. loss of
axons, can be better evaluated by ophthalmoscopic examination of the
peripapillary retina as the nerve fibers of the anterior visual pathway all have
to pass through the peripapillary area to reach the optic disc. They are easier
to visualize against the background of the retina and the choroid than
against the background of the disc supporting tissues. Admittedly, fundus-
topic evaluation of nerve fiber bundles requires training: this is why this
structure has escaped serious attention for so many years (Lundstrom 1977,
Vannas, Raitta & Lemberg 1977).
Diffuse loss of axons
Complete loss of the retinal nerve fiber layer is easily recognized because of
the resulting exposure of retinal and choroidal detail: small vessels can be
seen unobscured by overlying nerve fiber bundles throughout their course,
and minute detail characterizes also other retinal and choroidal structures.
The denuded retina has a finely mottled appearance. The optic disc margin,
of course, becomes very sharply defined with loss of overlying nerve fibers
(Hoyt, Frisen & Newman 1973, Lundstrom & Frisen 1975, 1976) (Fig.
1 B).
A partial loss of nerve fibers, uniformly distributed across the optic
nerve, is much more difficult to identify with present techniques, particular-
ly if it is bilateral. Cases with unilateral lesions, or asymmetrical bilateral
lesions, are best identified by juxta-positioning well focused fundus photo-
graphs, and looking for differences between the two eyes with regard to the
relative prominence of nerve fiber opacity, and the definition of small de-
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