MYOPIA, OPHTHALMOSCOPIC APPEARANCE. 37
These small atrophied spots often seem to lie at a different
level from the other parts of the fjindus, — at least it is often no-
ticed that the retinal vessels in passing from the periphery upon
the atrophied part experience a change of direction, which is to be
regarded as the expression of a transition from one surface to
another lying deeper. Donders* and Manthnerf regard these
cases as exceptional, and I have also formerly expressed my-
self in the same way, since in cases of a high degree of myopia,
with wide-spread choroidal atrophy, I missed the oplithalmo-
scopic signs of the difference of level. The case is somewhat dif-
ferent with the crescentic spots of moderate size with a breadth
less than that of the disc. Especially when they are sharply
bounded and surrounded by the dark line before described, do
they give the impression of a slight ectasia. The optic disc shows
generally in these cases where the ectasia affects it only on one
side, an oblique position, the side corresponding to the greatest
diameter of the ectasia lying deepest ; and besides this, we have
such a change of form of the optic nerve that its transverse sec-
tion forms an oval, whose shortest diameter lies in the same direc-
tion as that in M'hich the ectasia has attained its greatest extent.
This change of form of the optic nerve is, in part certainly, only
an apparent one; its dislocation toward the median wall of the
eyeball causes us to see it in a more oblique position than normal,
and therefore foreshortened ; still more must this be the case
where the disc has suffered the oblique excavation above described.
Where the choroidal atrophy is of slight extent, the contour of
the optic nerve is generally sharply distinguishable from the ad-
joining white scleral region. If the atrophy involves a large j^art
of the fundus, the demarcation of the optic disc generally becomes
very indistinct.
The retinal vessels show with unusual distinctness upon the white background of the sclera ; for this reason they are often visible in greater numbers ; they are, moreover, less sinuous than normal.
The choroid bordering upon the atrophied spot may appear wholly unchanged, but sometimes shoM'S traces of a slight degree of atrophy ; it appears somewhat lighter and more transparent,
- L. c, pag. 300. t L. c, pag. 421.
