thereby increased, the far point may be removed by concave glasses to about 12 inches; all strong convergence is to be avoided. If we suspect, as is frequent in high degrees of myopia in young individuals, that the symptoms of irritation are caused by spasm of the muscle of accommodation, the spasm is first to be relieved by the use of atropine, and the true degree of the myopia is then to be determined; the use of atropine can be continued several days, during which time the eyes should be protected from dazzling light by colored glasses. Upon a recurrence of the spasm of accommodation the use of the artificial leech is advisable.
The cases of diminished acuteness of vision which develop in the course of myopia, and which depend upon diseases of the vitreous, retina, or choroid, require a derivative treatment, and such eyes must be spared as much as possible.
The prognosis in these cases is, on an average, so much the better the fewer the material changes visible with the ophthalmoscope.
HYPERMETROPIA.
Hypermetropia exists when, accommodation being relaxed, parallel rays falling upon the cornea of the eye are focused at a point behind the retina. Under these circumstances every luminous point casts a circle of diffusion upon the retina. It is only by an effort of accommodation, or (since we are at present not regarding accommodation, but considering only the condition of refraction) by the help of convex lenses, that the image of the luminous point can be brought forward and cast upon the surface of the retina. In a hypermetropic eye, whose accommodation is fully relaxed, it is only rays already converging which, falling upon the cornea, are united upon the retina. The point behind the eye toward which they converge is called the far point. Of course only a convex lens of a certain focal length can give to parallel rays such a convergence as is necessary to cast an image from distant objects exactly upon the retina; this can happen only when the focal point of the lens and the far point of the eye coincide. Such a lens is called the neutralizing one; it expresses the grade of the hypermetropia. Strictly speaking, the distance between the lens and the eye must be taken into account just as in myopia. If for instance the rays must converge toward a point 12 inches
