17 Canton, The Arcus Senilis, London, 1863.
Since 1859, when Graefe18 by means of the ophthalmoscope first diagnosticated this condition of the retina (which Schweigger19 a year and a half later substantiated by anatomical proof, demonstrating a closure of the central artery by an embolus in it just behind the lamina cribrosa), embolism of the central artery of the retina has been a favorite explanation of all cases of sudden one-sided blindness. Since that date Sichel,20 Nettleship,21 Priestly Smith,22 and Schmidt23 have all published careful clinical studies of similar cases with autopsies. Embolism is less frequent in this situation than in many other parts of the body, and this, as has been pointed out by Foerster, is probably due to the fact that the ophthalmic artery is given off from the external carotid nearly at a right angle, and while it in turn again sends off its smallest branch—the central retinal artery—at nearly the same angle; consequently, emboli are more readily carried past their orifices into some other vascular area supplied by the main stem. Mauthner has suggested that the transitory but complete blindness which sometimes precedes embolism of the central artery may be due to the stoppage of the orifice of the artery (where it comes off from the ophthalmic artery) by a previous embolus which has been too large to enter the artery, and which, owing to the favorable position of the orifice, has been washed beyond into some of the other branches. In the majority of such cases the ophthalmoscope shows that the retinal arteries are diminished in size and partially filled with blood, while a white opacity of the fibre-layer of the retina extends centrifugally from the disc and between it and the macula lutea. When the opacity surrounds the latter, the fovea centralis (where the fibre-layer dies out) shows by contrast as a reddish or at times a cherry-red spot. The state of the disc itself appears to differ in different cases: some authors have described it as unusually pallid, whilst others claim that it still retains more or less of its natural pinkish hue. In cases reported,24 where the disc is said to be of normal color, this circumstance is probably due to collateral circulation which has been established with the ciliary vessels at the optic entrance. Where the obstruction of the artery is complete the blindness is permanent, and the disc and retina become atrophic. Embolism also occurs in the branches of the central retinal artery, and in such instances there is loss of a corresponding part of the field of vision. In some cases there is hemorrhagic infarction.25 It is never present in embolism of the main stem of the central retinal artery. Inasmuch as this latter vessel is an end-artery, the absence of infarction and subsequent sphacelus is interesting. The intraocular pressure probably prevents the back current of venous blood into the obstructed area, while the nearness of the vessels of the chorio-capillaris allows the retina to obtain sufficient nutriment to prevent death without allowing it to carry on its functions. In the case of embolism of a branch, all the retinal blood being under the intraocular pressure, there would be no hindrance to the entrance of venous blood from the areas of the retina supplied by other arterial branches, although, as above mentioned, the infarction is not present in all such cases. Thrombosis of the central retinal vein is also a rare affection, only recognized and diagnosticated of late years. Michel26 reports 7 cases, with plates of the ophthalmoscopic appearances in 4 of them. The patients were all between fifty-one and eighty-one years of age, and all had rigidity of the peripheral arteries. The suddenness of the attack recalls the symptoms of embolism, but in thrombosis the blindness is said never to be absolute. The ophthalmoscopic appearances are described as consisting of a diffuse and intense reddish haze of the fibre-layer of the retina, hiding the outlines of the disc and usually extending one and a half disc-diameters from it. This area of haze shows numerous small hemorrhages, mostly linear, in the direction of the retinal fibres, and beyond it the arteries and veins of the retina again become visible. The veins are dilated, excessively tortuous, and carry dark blackish blood. In the periphery of the retina the hemorrhages are rounded and splotchy, whilst a dark rounded hemorrhage occupies the fovea centralis. There is no swelling or prominence of the disc. When the thrombosis has been complete, atrophy of the intraocular end of the optic nerve follows. Zehender27 makes two classes of cases—the marasmic in old people, and the phlebitic in young—reporting an interesting case in a patient twenty-six years old. Leber28 details a case of hemorrhagic retinitis with thrombosis of some of the venous trunks in the retina, which were swollen to two or three times their usual calibre, and filled with very dark, almost blackish, blood: as they approached the disc they rapidly diminished in size, and were almost thread-like as they dipped into it. Galezowski29 cites two instances—one in a case of injury to the ciliary region, and one after injury to the eye by steam. In the latter, the thrombosis affected the artery, and the subject was forty-nine years of age.
18 A. f. O., v. 1, S. 136.
19 Vorlesunqen über den Gebrauch des Augenspiegels, S. 140.
20 A. Sichel, Archiv der Phys. Norm. et Path., No. 1, pp. 83-89 and pp. 207-218 (quoted by Leber).
21 R. L. O. H. Rep., vol. viii., pp. 9-20.
22 Brit. Med. Journ., 1874, April, p. 452.
23 H. Schmidt, A. f. O., xx., 2, pp. 287-307.
24 Vide case by Schmidt, Archiv f. Ophthalm., xx., 2, p. 288.
25 Knapp, Archives of Ophthalmology and Otology, vol. i. p. 84 (with plates), and Landesberg, in same journal, vol. iv. pp. 39, 40, have each given cases of embolism of a branch of the retinal artery, with infarction.