and its intervascular spaces in consequence of its stretching are somewhat widened.
This circumscribed choroidal atrophy is almost always present in myopia, and according to Donders there is a quite uniform average relation between the extent of the atrophy on the one hand and the degree of myopia and time of life on the other. It must be mentioned, however, that in this respect there are very considerable individual variations. The consecutive atrophy may be very slight, with a quite high degree of myopia; and, on the other hand, in emmetropes, and even in hypermetropes, these white, crescentic, slight ectasias are sometimes seen upon the temporal side of the disc; they are observed oftener in old than in young persons. The condition of refraction not considered, the ophthalmoscopic appearances in many of these cases are exactly the same as in myopia. On the other hand, however, it is unmistakable that in this matter there are very gradual transitions, so that in any given case one cannot be certain whether he has before him an atrophied crescent or a rather broad "scleral stripe."
At all events, the connection between myopia and atrophy of the choroid is undoubted. It only remains to be explained why it develops so constantly on the temporal border of the optic nerve, and not on that part of the choroid lying near the visual axis. It is to be remembered that around the optic nerve the choroid is closely attached to the sclera, that often too it sends fibrous processes into the nerve itself. At this place, therefore, the choroid cannot so easily escape the strain as it can in other localities where it is more loosely connected with the sclera. Now, since the eye is most distended in its antero-posterior diameter, it is easy to see why the choroidal atrophy should begin just upon the temporal side of the optic nerve.[1]
Nevertheless, the sharp demarcation which many of these cases show, proves that certain local causes limit the effect of the distention of the entire choroid to a sharply circumscribed region. So, too, the fact that the atrophy often extends entirely around the optic nerve shows that the nerve itself participates in the process. In this connection the widening of the space between the two
- ↑ Comp. Schweigger, Zur path. Anat. der Choroidea, Arch. f. Ophth., Bd, ix. 1, pag. 195, and Donders, Anomalien der Refraction, pag. 320.
