Case of the Month

Edited by Robert N. Johnson, MD

Case History

A 70 year-old man presents with a blurred superonasal visual field for the past 2 days.  His past medical history was relevant for diabetes mellitus, hypertension and dyslipidemia.  His past ocular history, family history, social history and medications were non-contributory.

On examination, best-corrected visual acuity was 20/25 in both eyes.  Intraocular pressure was normal in both eyes.  The anterior segment examination was unremarkable.  The posterior segment exam of the right eye was remarkable for a patch of retinal whitening and edema (figure 1A) with a yellow refractile embolus (see figure 1 inset) seen within the arteriole at the bifurcation of the artery along the inferior arcade.  In addition, scattered retinal hemorrhages, microaneurysms, and hard exudates consistent with non-proliferative diabetic retinopathy were found bilaterally (figure 1B).  Fluorescein angiography of the right eye (figure 2A and B) revealed nonproliferative diabetic changes with minimal findings of reduced flow in the interotemporal branch retinal artery due to the embolus

Spectral domain OCT (SD-OCT) of the right eye (figure 3) shows inner and middle retinal hyperreflectivity temporally, sparing the fovea.  SD-OCT of the left eye was unremarkable.  A horizontal SD-OCT cut through the Hollenhurst plaque demonstrates an endoluminal embolus (figure 4).  The en-face projection of the OCT angiography (OCTA) volume of the right macula delineates the retinal edema (figure 5).  The en-face OCTA over inferior arcade highlights the embolus (figure 6).  OCTA of the retina along the inferior arcade shows marked decrease in vascular perfusion distal to the embolus (figure 7).

Figures 2A and B:  Fluoresein angiography of an early transit phase in the right eye (FIgure 2A) of the right eye. Complete filling of the smaller branch just inferotemporal to the fovea is seen (red arrow), but incomplete filling is noted on the more distal branch (white arrow).  Fluorescein angiogram montage of the right eye (Figure 2B) shows nonproliferative diabetic retinopathy.

Figure 3:  SD-OCT of his right eye.  Inner and middle retinal hyperreflectivity temporally, sparing the fovea (arrows) is present.

Figure 4:  SD-OCT of his right eye with imaging oriented through arteriole and Hollenhorst plaque.

Differential diagnosis

Branch retinal artery occlusion, central retinal artery occlusion, cilio-retinal artery occlusion, ophthalmic artery occlusion.

Discussion

Retinal artery occlusions (RAO) typically present with sudden monocular, painless, vision loss.  Visual acuity may be affected if the artery supplies the macula, specifically the foveal region.  Otherwise, visual field loss may be noted.  Central retinal artery occlusions comprise over 50% the RAOs, while branch retinal artery occlusions (BRAO) consist of 40% and cilioretinal artery occlusions under 5%.¹

On clinical examination, retinal whitening will be seen due to inner retinal ischemia affecting the nerve fiber and ganglion cell layers.  Opacification of the retina can occur only in areas where the ganglion cell layer is thicker than one cell.  This is not the case in the fovea and thus a cherry-red spot is seen there.  Similarly so in the peripheral retina.  Embolic phenomenon is the most common cause of nonarteritic RAOs.  Most commonly, a yellow, refractile cholesterol embolus (70%) is seen, and less commonly is calcified (15%) or a platelet/fibrin embolus (15%).  Classically, cholesterol emboli which are also known as Hollenhorst plaques originate from the carotid arteries while the calcified emboli have a cardiac origin.  Fluorescein angiography, OCT, OCTA should be performed to aid in the diagnosis and prognosis of RAOs.²

Once a diagnosis of RAO has been made, carotid doppler testing and echocardiography should be performed for a systemic work up.  Giant cell arteritis should be ruled out and in atypical cases, a hypercoagulability work up should be performed (factor V Leiden, protein C, protein S, antithrombin III, homocysteine levels, sickle cell disease and antiphospholipid antibodies).¹    There is emerging evidence that for all RAOs, urgent diagnostic workup is needed as the risk of stroke is particularly increased during the first week after a RAO as both the retina and brain share the same arterial supply.³

Treatment of RAOs is challenging and controversial.  Based on Rhesus monkey experiments, the critical time period to attempt treatment is 3-4 hours before irreversible damage is suffered.  However, these studies had complete obstruction and humans rarely have complete obstruction. When patients presenting within 24 hours, an attempt should be made to reestablish flow.  Conventional therapy includes attempts to reduce intraocular pressure, dislodging emboli, dilation of ocular blood supply, and anticoagulation.  However, most successful treatments have been anecdotal and have not been proven effective.  Recently, more invasive therapy with use of intra-arterial tissue plasminogen activator (t-PA) was investigated in the EAGLE study.  However, this study proved not fruitful and was stopped early due to higher rates of complications.⁴

References

1. Ryan S.  Retina, 5th ed.  2013:  1012-1025.
2. Hayreh SS, Zimmerman MB. Fundus changes in branch retinal arteriolar occlusion. Retina. 2015 Oct 1;35(10):2060-6.
3. Park SJ, Choi NK, Yang BR, Park KH, Lee J, Jung SY, Woo SJ. Risk and Risk Periods for Stroke and Acute Myocardial Infarction in Patients with Central Retinal Artery Occlusion. Ophthalmology. 2015 Nov 30;122(11):2336-43.
4. Schumacher M, Schmidt D, Jurklies B, Gall C, Wanke I, Schmoor C, Maier-Lenz H, Solymosi L, Brueckmann H, Neubauer AS, Wolf A. Central retinal artery occlusion: local intra-arterial fibrinolysis versus conservative treatment, a multicenter randomized trial. Ophthalmology. 2010 Jul 31;117(7):1367-75