Central retinal artery occlusion associated with patent foramen ovale: a case report and literature review

1. Department of Ophthalmology & Visual Sciences, Montefiore Medical Center/AECOM, New York, USA. 2. Department of Ophthalmology, Bronx Lebanon Hospital Center of Icahn School of Medicine at Mt Sinai, New York, USA. 3. Department of Surgery (Ophthalmology), Jacobi Medical Center, New York, USA. 4. KLM Eye MDs, Brooklyn, New York, USA. 5. Department of Medicine (Cardiology), Jacobi Medical Center, New York, USA.


INTRODUCTION
Patent foramen ovale (PFO) is a connection between the right and left atria. During fetal development, presence of a PFO allow oxygenated maternal blood to bypass lung circulation and directly supply the arterial circulation. In most, the PFO closes spontaneously during infancy (1) . However, in 27% of the general population, this fetal shunt persists. In the absence of filtration in the lungs, emboli emanating from silent deep or superficial venous thrombosis traverse this shunt causing paradoxical emboli. The risk of stroke in those without comorbidities is only 0.1% (1) . However, in patients under 55 years, up to 46% of cryptogenic strokes have been attributed to PFO (1) .
Central retinal artery occlusion (CRAO), a stroke of the inner retina, presents as acute painless vision loss, typically resulting in 20/400 vison or worse (2) . It has an estimated incidence of 1 in 100,000 (2) , and has a mean age of presentation of 60 years (3) . The common etiolo gies include cardiac abnormalities, coagulopathies, myeloproliferative disorders, collagen vascular diseases, as well as other inflammatory diseases and malignancy. In approximately 45% of patients under 45 years of age, CRAO is associated with underlying cardiac abnormalities (4) . Besides profound vision loss affecting the functional capacity, patients are at increased risk of cerebral and cardiac ischemia, warranting evaluation of underlying etiologies.
Transthoracic echocardiography (TTE) is part of standard stroke workup to exclude cardiac etiology. It employs a non-invasive, ultrasound probe or transducer applied to the chest. Ultrasound waves are translated into video images to assess cardiac anatomy and physiology. Furthermore, bubble accentuated studies using intravenous injected agitated saline (gas added to saline) assess the cardiac flow. Even though this technique can reveal shunts, it cannot differentiate atrial septal defects from PFO.
Transesophageal echocardiogram (TEE) has been used to supplement TTE. A flexible probe with the ultra sound transducer at the tip is inserted into the esophagus, placing it more proximal to the heart. The signal-weakening effect of intervening thoracic structures is reduced, improving the resolution of cardiac images. Therefore, PFOs are easily visualized and quantified. Previous studies have determined that PFO is one of the most common cardiac defects determined using TEE in patients with cryptogenic embolic strokes, with PFO being detected after the initial TTE reported no abnormal findings (5) . Herein, we report an illustrative case of CRAO associated with PFO. We reviewed the English literature for similar cases and explored the types of echocardiograms required to disclose this cardiac anomaly.

CASE REPORT
A 43-year-old male with a history of hypertension presented with sudden painless right vision loss. Exa-mination revealed best-corrected visual acuities of no light perception (right) and 20/25 (left) and right relative afferent pupillary defect. Intraocular pressures were normal, extraocular movements were full, and anterior segments were unremarkable. Dilated fundus examination revealed a right pale, moderately swollen optic nerve, macular pallor with a cherry red spot, and box-carring blood flow in several vessels. However, emboli were not detected. The left eye was normal. Right central retinal artery occlusion was diagnosed, and the patient was transferred to the Stroke Unit for admission and management. Blood pressure on admission was 136/92 mmHg. Exa mination the next day revealed resolution of box--carring and a more distinct cherry red spot ( Figure 1A). The left eye remained normal ( Figure 1B). Fundus fluo-    The patient's hospital course was uneventful, and he was discharged on lisinopril, nifedipine, aspirin, and atorvastatin. At the one-month follow-up, right visual acuity improved to count fingers and fundus examination revealed resolution of retinal pallor without evidence of neovascularization. A silent venous thrombo-emboli traversing the PFO was thought to be causally related to the CRAO. The patient was referred to another center for consideration of PFO closure to reduce the risk of additional ischemic vasculo-occlusive events.

DISCUSSION
Our case demonstrated a young patient presenting with CRAO with initially negative cardiovascular and neurologic workup. Although initial TTE bubble study revealed a right to left atrial shunt, it was not diagnostic for PFO. TEE was diagnostic for PFO and verified the location and size. This observation has implications for pursuing TEE in young patients after cryptogenic vascular events. Even though our patient had a history of hypertension and investigations disclosed hyperlipidemia that could have contributed to CRAO, both conditions were deemed mild and likely noncontributory. Hence, the PFO was considered to be the likely cause of CRAO.
Although a prospective, randomized, controlled study with uniform investigations and standardized instrumentation would provide better evidence-based support for the initial investigative protocols of young patients presenting with retinal artery occlusions, our case and the previous reports affirm that TEE has a higher diagnostic yield for PFO than TTE (Table 1). Therefore, providers should consider TEE during the initial workup of young patients with cryptogenic CRAO.  In addition, we would like to thank Luisamely Cruz, COA and Joseph Gonzalez, COA at Jacobi Medical Center Ophthalmology Department, for technical support with ancillary tests and images used in this report.