. A treatise on the diseases of the eye. , moreover, thatin hypermetropia there often exists a typical form of face, chiefl)^ dependentupon the shallowness of the orbit, wlaich lends a peculiar flatness to thephysiognomy. The hypermetropic construction of the eyeball is congenital,and often hereditary. [In the hypermetropic eye, the line of vision deviates inward from thecorneal centre more than in emmetropia. It may develop during the growthof the body, but it is acquired comparatively seldom; aphakia being themost frequent cause of acquired hypermetropia. Hypermetropia may alsobe caused by t
. A treatise on the diseases of the eye. , moreover, thatin hypermetropia there often exists a typical form of face, chiefl)^ dependentupon the shallowness of the orbit, wlaich lends a peculiar flatness to thephysiognomy. The hypermetropic construction of the eyeball is congenital,and often hereditary. [In the hypermetropic eye, the line of vision deviates inward from thecorneal centre more than in emmetropia. It may develop during the growthof the body, but it is acquired comparatively seldom; aphakia being themost frequent cause of acquired hypermetropia. Hypermetropia may alsobe caused by the retina being pushed forward by exudations beneath it, orby a flattening of the eyeball posteriorly by orbital tumors. ( Schweigger,1. )] The ophthalmoscope also enables us to diagnose a hypermetropic eye, but iathis case just the reverse obtains to what was seen in the myopic eye. I. The fundus may also in this case be seen in the erect image at a con-siderable distance, but we obtain an erect image of it (and not, as in a reverse image), for if we regard the optic nerve or one of the retinalvessels, and move our head to one side, we find that the image moves in thesame direction. For an explanation of this, let us glance at Fig. 202. Let a be the hypermetropic eye, b the eye of the observer; a is adjustedfor its far point (convergent rays), and the rays reflected from its back- 4] 642 ANOMALIES OF REFRACTION AND ACCOMMODATION. ground will, consequently, emanate from it in a divergent direction, as ifthey came from a point behind the retina, and they must, therefore, also fallin a divergent direction upon the eye of the observer. If the latter ismyopic (adjusted for divergent rays), the rays will be united upon his retinawithout the aid of any correcting lens behind the ophthalmoscope. But ifhis eye is emmetropic (adjusted, when in a state of rest, for parallel rays), hewill either have to place a convex lens behind the mirror, or have to accom-modate for a nea
Size: 3047px × 820px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booksubjecteye, booksubjecteyediseases, bookyear
