OPHTHALMOSCOPY OF THE VERTEBRATE EYE 



31 



depression, the physiologic excavation, which 

 marks the divergence of nerve-fibres. The 

 excavation is funnel-shaped, the base being 

 anterior. A trace of the hyaloid artery of 

 fetal life is occasionally seen here as a thread 

 of connective tissue running from the papilla 

 into the vitreous. Surrounding the papilla 

 are two rings: an inner, due to exposure of 



fibres, due to the fact that the medullary cover- 

 ing of the axis-cylinders exists in the fibre-layer 

 of the retina. In such a case the fundus shows 

 a patch of a brilliant white color extending out 

 from the disc. Generally the white area is in 

 contact with the disc. It rarely occurs that 

 the opaque fibres are found at a great distance 

 from the nerve-head or that they occupy a 





Fig. 22 



Diagram Showing the Relations of the Parts in the Human Fundus Oculi. a, sclera; b, choroid; c, retina; 



I, macular region; 2, optic disc; 3, superior nasal artery; 4, inferior nasal artery; 5, inferior 



temporal artery; 6, superior temporal artery; T, temporal side; N, nasal side. 



the sclera, is whitish, and is called the scleral 

 ring; and an outer one, due to the showing of 

 choroidal pigment, is named the choroidal 

 ring. At the bottom of the excavation a 

 few dark spots are seen, from the gray stip- 

 pling of the lamina cribrosa. In color the 

 papilla is grayish-pink or reddish, and stands 

 out in marked contrast to the reddish-yellow 

 of the remaining parts of the fundus. The 

 color of the papilla varies with the age and 

 complexion of the individual, the color of the 

 surrounding parts of the fundus, and with 

 the illumination used. A common anomaly 

 is the presence or persistence of opaque nerve- 



large area of the fundus. The physiologic cup 

 or depression may occupy a large part of the 

 nerve-head, but never extends to the scleral 

 ring. Under normal conditions many varia- 

 tions are seen in the size and depth of the cup 

 and in the arrangement of the blood-vessels. 



The blood-vessels are the central artery and 

 vein of the retina. They run in the nerve- 

 fibre layer of the retina, and often present 

 variations of distribution. The middle of 

 the fovea centralis has no blood-vessels. 



While it is often stated that the retinal 

 vessels can be seen on ophthalmoscopic ex- 

 amination, as a fact it is the column of blood 



