The student's guide to diseases of the eye . ction ofan eye in which the lower part of the retina is se-parated. The separated portion is usually far within thefocal length of the eye ; its erect image is, thereforevery easily visible by the direct method (p. 49, 1),.when it appears as a dark grey, or whitishreflexion in some part of the field, the remainderbeing of the natural red colour; the detached partis grey or whitish, because the retina has becomeopaque. With care we can accurately focus thesurface of the grey reflexion, see that it is folded,and see one or more retinal vessels meander
The student's guide to diseases of the eye . ction ofan eye in which the lower part of the retina is se-parated. The separated portion is usually far within thefocal length of the eye ; its erect image is, thereforevery easily visible by the direct method (p. 49, 1),.when it appears as a dark grey, or whitishreflexion in some part of the field, the remainderbeing of the natural red colour; the detached partis grey or whitish, because the retina has becomeopaque. With care we can accurately focus thesurface of the grey reflexion, see that it is folded,and see one or more retinal vessels meandering uponit in a tortuous course; they appear small and of darkcolour. If the separation be deep the outline of itsmore prominent folds (Fig. 77) can be seen standingout sharply against the red background, and in somecases the folds flap about when the eye is quicklymoved. In extreme cases we can see the detachedpart by focal light. When the detachment is recent,especially if shallow, the red choroid is still seen. 190 DISEASES OF THE RETINA. Fig. 77. — Ophthalmosco-pic appearance of de-tached retina (erectimage) (after Weckerand Jaeger). through it; the diagnosis then rests on the observa-tion of whether the vessels in any part become darker,smaller, and more tortuous, and upon ophthalmo-scopic estimation of the re-fraction of the retinal vessels(p. 51) at different parts ofthe fundus, for the detachedpart will be much more hy-permetropic than the very high myopia a shal-low detachment may still liebehind the principal focus,and therefore not yield anerect image without a suit-able concave lens ; in such acase, and in others whereminute rucks or folds of de-tachment are present, exami-nation by the indirect methodleads to a right diagnosis; the image of the detachedportion is not in focus at the same moment as its sur-rounding parts, parallactic movement* is obtained, andthe vessels are tortuous. Deep and extensive detach-ment is often associated with opacities in the
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