The student's guide to diseases of the eye . s wide, shallow, and enlarged towardsthe outer side of the disc. The physiological pit iswhiter than the rest of the disc, because the greyish-pink nerve-fibres are absent at this part, and we cantherefore see down to the opaque, white, fibroustissue which, under the name of lamina cribrosa,forms the floor of the whole disc (Fig. 35). Thestippled appearance often noticed in the pit is causedby the holes in this lamina, through which thebundles of nerve-fibres pass on their way to theretina ; the holes appear darker because filled bynon-medullated ne
The student's guide to diseases of the eye . s wide, shallow, and enlarged towardsthe outer side of the disc. The physiological pit iswhiter than the rest of the disc, because the greyish-pink nerve-fibres are absent at this part, and we cantherefore see down to the opaque, white, fibroustissue which, under the name of lamina cribrosa,forms the floor of the whole disc (Fig. 35). Thestippled appearance often noticed in the pit is causedby the holes in this lamina, through which thebundles of nerve-fibres pass on their way to theretina ; the holes appear darker because filled bynon-medullated nerve-fibres, which reflect but littlelight. OPHTHALMOSCOPIC EXAMINATION 47 The other parts of the fundus.—The groundwork isof a bright fiery red (the choroid not the retina) ;in many eyes this colour is nearly uniform, but inpersons of very light or very dark complexion we seea pattern of closely-set, tortuous, red bands (vesselsof the choroid), separated by spaces either of darkeror of lighter colour (Fig. 32). (For details seeChap. XII.). FlG. 32.—Ophthalmoscopic appearances of healthy fundus in aperson of very fair complexion. Scleral ring well eye, inverted image. (Wecker and Jaeger.) Upon this red ground the vessels of the retina di-vide and subdivide dichotomously. It will be noticedthat the chief trunks pass almost vertically upwardsand downwards, and that no large branches go to thepart apparently inwards from the disc (to the leftin the Fig.) ; that the visible retinal vessels arecomparatively few and are widely spread ; that theybecome progressively smaller as they recede fromthe optic disc; and that they never anastomose witheach other. Special attention must be given to thepart, apparently to the inner (nasal) side of the optic 48 OPHTHALMOSCOPIC EXAMINATION disc (really to its outer, temporal side), which is theregion of most accurate vision, the yellow spot (y. s.,macula lutea, or shortly macula ). In this region,which comes into view when the patie
Size: 1572px × 1590px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booksu, booksubjecteye, booksubjectophthalmology
