With occlusions of smaller branches of the central retinal artery by emboli, one may be able to see the occluding material. Most frequently observed are Hollenhorst plaques—glistening, white-yellow atheromatous particles (Fig. 12-9) seen in 40 of 70 cases of retinal embolism in the series of Arruga and Sanders. These plaques can also be an asymptomatic manifestation of carotid or aortic atherosclerosis. Intraluminal particles may alternatively have the appearance of white calcium from aortic or mitral valves or atheroma of the great vessels. Red or white fibrin-platelet emboli may emanate from the heart, its valves, or other sources. Emboli to retinal artery branches may be difficult to see without fluorescein retinography; furthermore, most of these emboli soon disappear. Central and branch retinal artery occlusions also occur as a consequence of hypercoaguable states, including anti-phospholipid antibody syndrome. Giant cell arteritis is another important cause; patients who are in their fifties or older should be screened for this condition.
It has become routine in some centers to treat acute central retinal artery occlusion in an urgent manner with a number of methods in the hope that the embolus or thrombus will be propelled into more distal vessels. These treatments are generally aimed at lowering intraocular pressure (acetazolamide, inhalation of carbon dioxide; paracentesis of the anterior chamber, ballottement), to dilate the vessels, and reestablish flow. We can only offer the impression that these procedures have generally often not been successful. Some case series have suggested that local thrombolysis with intraarterial agents may be useful, although a multicenter controlled trial of thrombolysis (Eagle Study cited under Schumacher and colleagues) was halted early because of concerns about safety.
Retinal venous occlusion Because the central retinal artery and vein share a common adventitial sheath, atheromatous plaques in the artery can provoke thrombosis of the retinal vein. This results in a spectacular display of retinal lesions that differs from the picture of central retinal artery occlusion. The veins are engorged and tortuous, and there are multiple diffuse “dot-and-blot” and streaky linear retinal hemorrhages (Fig. 12-10). Retinal vein thrombosis is observed most frequently with diabetes mellitus, hypertension, and leukemia; less frequently with sickle cell disease; and rarely with multiple myeloma, and Waldenstrom macroglobulinemia in relation to the hyperviscosity that these two diseases cause. Sometimes, no associated systemic disease can be identified, in which case the possibility of an orbital mass (e.g., optic nerve glioma) should be considered. In retinal vein thrombosis, visual loss is variable and there may be recovery of useful vision. In cases where macular edema ensues, recovery may be enhanced by laser photocoagulation.
Benign retinal vasospasm and migraine In addition to the typical ischemic cause of this syndrome, transitory retinal ischemia is observed occasionally as a manifestation of migraine. Rarely, benign vasospasm of the central retinal artery may be implicated as a cause of recurrent transient monocular blindness, in which case the episodes may cease with the introduction of a calcium channel blocker, as reported by Winterkorn and colleagues.
Other Diseases of the Retina
Aside from vascular lesions, tears and detachments of the retina may impair vision acutely. The most common form of detachment is a separation of the pigment epithelium layer from the sensory retina with fluid accumulation through a tear or hole in the retina. In so-called traction detachment—observed in cases of premature birth or proliferative retinopathy secondary to diabetes or other vascular disease—contracting fibrous tissue pulls the retina from the choroid.