Page:Handbook of Ophthalmology (3rd edition).djvu/40

34 much as in uncomplicated myopia the protrusion is by no means so circumscribed and prominent as in anterior scleral staphyloma. In spite of the elongation of the axis, the eye maintains, as shown in Fig. 8, a regular form. The sclera is expanded and thinned throughout its whole extent, on the temporal more than on the median side, and most of all in the region of the posterior pole. So thin may it become that this part upon enucleated eyes appears blue, like an anterior staphyloma, and if the cornea be turned to the light, an inverted image of outer objects will be plainly seen cast upon the attenuated portion. Indeed, even during life the bluish color in the region of the posterior pole can be often seen by causing the patient to turn his cornea strongly inward.

Fig. 8.

After Domlers, Anomalien der Refraction, etc, Fig. 145.

These changes exert a marked influence upon the place where the optic nerve enters the eye.

The stretching of the membrane in the region of the posterior pole pushes the optic nerve somewhat aside toward the median line.

Fig. 9.

From Bonders, l. c. Fig. 147. The space c between the inner and outer nerve-sheaths widens as it approaches the sclera; the largest part of the outer sheath a" blends with the sclera; a thinner membrane, a', runs toward the optic nerve, and is continuous with the inner nerve-sheath b'. At this place the sclera consists therefore of only a thin lamella, a', which is in relation posteriorly with the loose areolar tissue c', and which anteriorly is covered by the atrophied and depigmented choroid d'; f is the lamina cribrosa, and the tissue n, above the choroid, is the retina.

Moreover, the two nerve-sheaths change in their relations toward each other. Since the inner nerve-sheath is adherent to the nerve itself, while the outer one is continuous with the sclera, it follows that a distention of the latter causes a traction upon the external sheath, drawing it from the other and increasing the space between the two. (See Fig. 9.)