Page:Handbook of Ophthalmology (3rd edition).djvu/42

36 more or less atrophy of the choroid exists. In many cases it is only the pigmented epithelium, which is faded or degenerated so that the choroidal stroma can be distinctly seen. In most cases, however, there is an unmistakable atrophy of the stroma, and the entire choroid is transformed into a thin, structureless, transparent membrane, which does not weaken in any degree the white reflex from the sclera. In many cases one still sees a few large vessels remaining in the region of the choroidal atrophy. These various appearances are observed quite constantly. Often with a high degree of myopia, and with an atrophied part equal in width to the diameter of the disc, only the pigment-epithelium will have lost its color, while in other cases of a mild form of myopia there will be only a small but fully atrophied crescent about the margin of the disc.

The atrophied part is often separated from the adjoining choroid by a rather regular dark line. Some cases, where the atrophy has extended farther over the choroid, show traces of several such concentric curved lines. In other cases the atrophied part has a more or less irregular form.

In the majority of cases this circumscribed choroidal atrophy occurs on the temporal side of the optic nerve, and spreads from it toward the macula lutea, generally, however, without reaching it. The increase of the atrophied region does not depend alone upon an implication of the adjoining choroidal tissue in the degenerative process, but at the same time upon a further stretching of the already thin and yielding part; in this way the distance between the macula lutea and the optic nerve increases, and the latter becomes more displaced toward the median line.

In high degrees of myopia the choroidal atrophy often extends around the entire optic nerve; the disc appears surrounded by a white ring, whose breadth is generally greater on the temporal than on the median side.

In rare cases the atrophied spot is below the optic nerve; oftener its position is under and outward, or over and outward, from the optic nerve. Its rarest position is above the optic nerve, and such cases do occur. A beginning of the choroidal atrophy upon the median side of the optic nerve has been observed.