Diagnosing retinal artery occlusions

Retinal vascular disease can be difficult to accurately diagnose. There are a myriad of retinal disorders such as retinal phlebitis, retinal arteritis, intraretinal infiltrates, necrotizing retinitis, posterior scleritis, and chorioretinitis that can present with similar findings and complicate the diagnosis.

Retinal arterial occlusive disease can manifest as several different variations. The most common include central retinal artery occlusion (CRAO), branch retinal artery occlusion (BRAO), and cilioretinal artery occlusion (CLRAO). Almost all cases of retinal arterial occlusions (RAO) are caused by a thrombus, embolus, or thrombo-embolus.

A thrombus is a blood clot that is formed by blood coagulation in hemostasis. An embolus is any detached, traveling intravascular mass (solid, liquid, or gaseous) carried by normal circulation from one part of the body to a distal site.

A thrombo-embolus is a blood clot that detaches from the original site of coagulation and is carried by normal blood circulation to a site distant in the body.¹ Other rare documented etiologies of RAOs include migraine, ocular surgery, intravitreal injections, chiropractic care, and infection.²

Related: A closer look at central retinal artery occlusion

Central retinal artery occlusion

The diagnosis of a CRAO in the acute phase is rather straightforward. Patients will often present with a history of sudden and profound vision loss, an afferent pupillary defect, opaque retina, cherry red spot, and retinal arterial attenuation. Less common findings in the acute phase include optic nerve swelling and optic disc pallor.³

A retinal embolus may be detectable in 23 percent of these cases.³ Prior reports indicate that 75 percent of these emboli are composed of cholesterol, 10 percent are calcific, and 15 percent are fibrinous.⁴

It can be more difficult to make the appropriate diagnosis when a patient presents with an old CRAO. Many patients with a CRAO do not recover vision after the insult and will have a best-corrected visual acuity (BCVA) in the 20/400 to light perception range. The patient will also have signs of arteriolar and venous narrowing, optic atrophy, an absent cherry red spot, and possibly arteriolar sheathing.³

It is important to note that retinal neovascularization is significantly less common with any RAO as compared to a vein occlusion; this is because vascular endothelial growth factor (VEGF) is released by hypoxic retina, not infarcted retina. This is not to say that neovascularization due to CRAO is impossible, however.

A recent study found the prevalence of neovascularization development to be 18 percent in patients with CRAO at an average of 8.5 weeks.⁵

Next: Branch retinal artery occlusion

Branch retinal artery occlusion

The ocular findings of a BRAO are similar to that of a CRAO. The vision can range from 20/20 to 20/400, depending on the portion of retina that is affected. Careful pupil testing is essential because a Wernicke’s reaction can be present.⁶ Additionally, a subtle cherry red spot may be visible in the acute phase if a temporal arterial branch is affected.

An old BRAO will resemble an old CRAO except that the findings will be limited to one quadrant of the retina and the optic nerve. Arteriolar and venous narrowing, partial optic atrophy, and arteriolar sheathing are other possible diagnostic findings.

If you see the following unilateral signs during your examination, your patient may have had a BRAO or CRAO in the past: 

• Decreased vision

• Presence of an APD

• Unilateral visual field defects

• Arteriolar sheathing

• Arteriolar narrowing

• Retinal atrophy

• Optic atrophy

Next: Cilioretinal artery occlusion

Cilioretinal artery occlusion

The cilioretinal artery emanates from the temporal side of the optic nerve and is present in roughly 32 percent of the population.⁷ This artery is unique in that it originates from the choroidal circulation, providing a dual blood supply to the macula.⁸ Unfortunately, cilioretinal arteries can also become occluded. There are three clinical varieties of cilioretinal artery occlusion (CLRAOs): isolated CLRAO, CLRAO in conjunction with a central retinal vein occlusion, and CLRAO with arteritic ischemic optic neuropathy.  

Isolated CLRAOs tend to have a good visual prognosis because of persistent blood supply from the central retinal artery. The second variety, CLRAO with vein occlusion, also tends to have a good prognosis. The comorbid vein occlusion is frequently non-ischemic, thus any visual deterioration is dependent on the extent of macular edema.

A CLRAO with arteritic ischemic optic neuropathy holds a poor visual potential because the short posterior ciliary arteries become infarcted, affecting both the optic nerve and the cilioretinal artery.⁹

Systemic diagnosis

Dr. Theodore Woodward is credited with coining the old medical proverb, “When you hear hoof beats, think horses, not zebras.” This principle also holds true for the diagnosis of systemic conditions associated with retinal artery occlusions. The most common systemic diseases associated with RAOs include arterial hypertension, ischemic heart disease, renal disease, carotid atherosclerosis, and diabetes mellitus.¹⁰

A retinal artery occlusion in patients older than age 50 warrants systemic evaluation to include blood pressure, complete blood count (CBC), hemoglobin A1C, fasting blood sugar, lipid profile, carotid duplex, and transesophageal echocardiogram (TEE). (TEE is an invasive procedure involving sedation. There is also a noninvasive test called a transthoracic echocardiogram (TTE).

Studies have shown a clear superiority of TEE over TTE when identifying a cardiac embolic source in patients with transient ischemic attack (TIA) or stroke.¹¹) Additionally, if the fundus examination does not reveal a retinal embolism, the appropriate testing should be performed to rule out temporal arteritis as a possible etiology.¹²

The above systemic conditions should also be considered in a young patient with a RAO. However, less common disorders that cause RAO should also be ruled out, including migraine, optic nerve head drusen, coagulopathies, coagulative effects of oral contraceptive medications, pancreatitis, trauma, tumor metastases, syphilis, sickle cell disease, migraine, and collagen vascular disorders, among others.^13,14

A thorough patient history and review of systems can help target which of these conditions is most likely for a specific patient.

Labwork for these “zebras” is helpful in identifying the underlying cause. Consider ordering a sickle cell electrophoresis, vasculitis screening profile, homocysteine, antiphospholipid antibody, cardiolipin antibodies, antinuclear antibodies, fluorescent treponemal antibody absorbed, (FTA-ABS,) venereal disease research laboratory (VDRL) test, or other tests that support the patient’s review of systems. 

Next: Retinal artery occlusion treatment

Retinal artery occlusion treatment

Effective treatment for central and branch retinal artery occlusions remains elusive. Multifarious therapies spanning from conservative to invasive have been attempted with varying results. Achieving a universally accepted treatment protocol is difficult because of the short window of opportunity to intervene after the occlusive event.

In experimental models of a complete CRAO, the time frame of retinal ischemia without permanent retinal damage is just over 90 minutes.^15,16 In a true clinical setting, the arterial occlusion can be incomplete, and a visual recovery may be achieved even after delays up to 24 hours.¹⁷

Conservative treatments attempt to increase the perfusion pressure to the eye in hopes of dislodging the precipitant to minimize the extent of retinal damage. Consider that retinal vascular perfusion pressure is equal to the mean blood pressure minus the intraocular pressure (IOP). Conservative therapies such as ocular massage, anterior chamber paracentesis, and glaucoma medications aim to rapidly decrease the IOP in order to foster increased perfusion.

Other treatments such as pentoxifylline, nitroglycerin, rebreathing carbon dioxide, and carbogen dilate the retinal arteries, which lessens blood flow resistance.² Enhanced external counterpulsation (EECP) is a treatment modality primarily used for patients with angina pectoris symptoms; research has shown EECP can also improve retinal blood flow and visual outcome in acute RAO.¹⁸ Hyperbaric oxygen therapy has also been documented to improve visual acuity in a small series of patients.¹⁹

Intra-arterial fibrinolysis (IAF) is an invasive treatment that attempts to dissolve the precipitant in the central retinal artery via a local infusion of tissue plasminogen activator. IAF uses a catheter to approach the ophthalmic artery where the fibrinolytic agent is then released.

Although the principle behind this treatment is sound, the results of IAF studies have been quite mixed. A retrospective, nonrandomized study reported a potential benefit of this treatment when compared with conservative management.²⁰

In contrast, a recent prospective randomized controlled trial comparing IAF to conventional management found no difference in visual outcomes between the two groups. This trial also showed an increased risk of cerebral hemorrhage with IAF, and thus does not recommend IAF as a suitable treatment option.²¹

The Cochrane Database reviewed all CRAO treatment literature up to 2009 and determined that no treatment modality was consistently successful. However, several small controlled case studies utilizing EECP and oral pentoxifylline have shown promising results.²²

If you encounter an acute RAO, do your best improve the retinal blood perfusion to dislodge the embolus. Proper diagnosis is only half the battle. A proposed cause of the occlusion should be identified because a retinal artery occlusion is highly correlated with underlying systemic disease.

Be sure to take a thorough history and review of systems to rule out potential contributing etiologies. Diagnosing a prior artery occlusion can be a challenge. Use the exam findings to help piece together the puzzle. While optometrists are fully capable of managing RAOs, do not hesitate to work with your local retinal specialist and the patient’s medical team when necessary.  

References:

1. Lusby FW. Retinal artery occlusion. Medline Plus. 2014 May 8. Available at http://www.nlm.nih.gov/medlineplus/ency/article/001028.htm. Accessed 07/21/15.

2. Hedges TR. Central and branch retinal artery occlusion. UpToDate. 2013 May 8. Available at http://www.uptodate.com/contents/central-and-branch-retinal-artery-occlusion. Accessed 07/21/15.

3. Hayreh SS, Zimmerman MB. Fundus changes in central retinal artery occlusion. Retina. 2007 Mar;27(3):276-89.

4. Arruga J, Sanders MD. Ophthalmologic findings in 70 patients with evidence of retinal embolism. Ophthalmology.1982 Dec;89(12):1336-47.

5. Rudkin AK, Lee AW, Chen CS. Ocular neovascularization following central retinal artery occlusion: prevalence and timing of onset. Eur J Ophthalmol. 2010 Nov-Dec;20(6):1042-6.

6. Kawasaki A. “Chapter 16: Disorders of pupillary function, accommodation, and lacrimation.” Walsh and Hoyt’s Clinical Neuro-Ophthalmology. 6th ed. Eds. Miller NR, Newman NJ. Philadelphia, PA: Lippincott Williams & Wilkins 2005. Page 739.

7. Justice J Jr., Lehmann RP. Cilioretinal arteries. A study based on review of stereo fundus photographs and fluorescein angiographic findings. Arch Ophthalmol. 1976 Aug;94(8):1355-8.

8. Brown GC. “Chapter 76: Retinal arterial obstructive disease.” Retina. 2nd ed. Eds. Schachat AP, Murophy RP. St. Louis, MO: Mosby –Year Book, Inc. 1994. Page 1370.

9. Hayreh SS, Podhajsky PA, Zimmerman MB. Branch retinal artery occlusion: natural history of visual outcome. Ophthalmology. 2009 Jun;116(6):1188-94.e1-4.

10. Hayreh SS, Podhajsky PA, Zimmerman MB. Retinal artery occlusion:  Associated systemic and ophthalmic abnormalities. Ophthalmology. 2009 Oct;116(10):1928-36.

11. de Bruijn SF, Agema WR, Lammers GJ, van der Wall EE, Wolterbeek R, Holman ER, Bollen EL, Bax JJ. Transesophageal echocardiography is superior to transthoracic echocardiography in management of patients of any age with transient ischemic attack or stroke. Stroke. 2006 Oct;37(10):2531-4

12. Hayreh SS, Zimmerman B. Management of giant cell arteritis. Our 27-year clinical study: new light on old controversies. Ophthalmologica. 2003 Jul-Aug;217(4):239-59.

13. Brown GC, Magargal LE, Shields JA, Goldberg RE, Walsh PN. Retinal arterial obstruction in children and young adults. Ophthalmology. 1981 Jan;88(1):18-25.

14. Greven CM, Slusher MM, Weaver RG. Retinal arterial occlusions in young adults. Am J Ophthalmol. 1995 Dec;120(6):776-83.

15. Hayreh SS, Kolder HE, Weingeist TA. Central retinal artery occlusion and retinal tolerance time. Ophthalmology. 1980; 87: 75-78.

16. Hayreh SS, Zimmerman MB, Kimura A, Sanon A. Central retinal artery occlusion. Retinal survival time. Exp Eye Res. 2004 Mar;78(3):723-36.

17. Richard G, Lerche RC, Knospe V, Zeumer H. Treatment of retinal arterial occlusion with local fibrinolysis using recombinant tissue plasminogen activator. Ophthalmology. 1999 Apr;106(4):768-73.

18. Werner D, Michalk F, Harazny J, Hugo C, Daniel WG, Michelson G. Accelerated reperfusion of poorly perfused retinal areas in central retinal artery occlusion and branch retinal artery occlusion after a short treatment with enhanced external counterpulsation. Retina. 2004 Aug;24(4):541-7.

19. Murphy-Lavoie, Butler F, Hagan C. Central retinal artery occlusion treated with oxygen: a literature review and treatment algorithm. Undersea Hyperb Med. 2012 Sep-Oct;39(5):943-53.

20. Beatty S, Au Eong KG. Local intra-arterial fibrinolysis for acute occlusion of the central retinal artery: a meta-analysis of the published data. Br J Ophthalmol. 2000 Aug;84(8):914-6.

21. Schumacher M, Schmidt D, Jurklies B, et al. Central retinal artery occlusion: local intra-arterial fibrinolysis versus conservative treatment, a multicenter randomized trial. Ophthalmology. 2010 Jul;117(7):1367-75.e1.

22. Fraser SG, Adams W. Interventions for acute non-arteritic central retinal artery occlusion. Cochrane Database Syst Rev. 2009 Jan 21;(1):1-16.