Visualization of the retinal vasculature is critical to evaluate and assess vascular structure and blood flow in many conditions.1–3 Fluorescein angiography (FA)4 has been able to reveal approximately 50% of the superficial retinal vasculature but is unable to provide clear images of the deeper vascular layer.5
More recently, optical coherence tomography (OCT), previously used strictly for structural studies, has been used to study vascularity and blood flow. OCT angiography (OCTA) provides a noninvasive approach to acquire high-resolution images of the retinal microvasculature.6
Here, we discuss the use of spectral-domain OCTA (SD-OCTA) to visualize the retinal vasculature in a patient presenting with a central retinal artery occlusion (CRAO). To our knowledge, this is the first use of this imaging technique for the diagnosis of CRAO.
A 65-year-old white man with a history of a Cognard Type IIA and IIB dural arteriovenous fistula (dAVF) presented with a hemivisual field defect in his left eye of 1-day duration. One day prior to presentation, the patient underwent an embolization procedure for the dAVF involving the superior sagittal sinus and left external carotid artery, likely causing multiple emboli to enter the ophthalmic artery and lead to his CRAO.
Visual acuity at this time was 20/25 Snellen in both eyes with correction, and intraocular pressures were recorded at 15 mm Hg in the right eye and 14 mm Hg in the left eye. A relative afferent pupillary defect was noted in the left eye.
Ophthalmic exam revealed a white, ischemic macula with areas of sparing and retinal edema as evidenced by fundus photography (Figure 1). The macular edema was evaluated further with generation of a macular thickness map (Figure 2). OCTA provided detail on retinal vessel perfusion, again emphasizing the presence of an area of perfused retina (Figure 3).
Color fundus photograph of the left eye demonstrating macular retinal edema consistent with a central retinal artery occlusion. The vessels show narrowing and stasis with some boxcarring. There is perfused retina superonasally in the macula consistent with an area of sparing.
A 6 mm × 6 mm macular thickness map registered on a laser scanning ophthalmoscope fundus image demonstrating macular edema in the areas of whitening seen on clinical exam and color fundus photography. The area of arterial sparing superonasally does not have edema.
Montage optical coherence tomography angiogram (3 mm × 3 mm cube centered on the optic nerve and 6 mm × 6 mm cube centered on the fovea) registered on a laser scanning ophthalmoscope fundus image. This central retinal artery occlusion has areas of arterial sparing, whereas the capillaries are globally absent nasal to the optic nerve and throughout most of the macular cube.
Scanning Protocol and Image Generation
The eye was imaged using a prototype SD-OCT instrument modified to perform OCTA (Cirrus; Carl Zeiss Meditec, Dublin, CA), approved by the Stanford University Human Subjects Institutional Review Board. Two scanning patterns were performed. The first covered an area of 3 mm × 3 mm with 245 A-scans per B-scan and a total of 245 B-scans per cubic volume, with four times oversampling. The second scan pattern was taken over a 6 mm × 6 mm area with 350 A-scans per B-scan, with 350 B-scans/cube and two times oversampling.
The resulting data were analyzed using the optical microangiography algorithm (OMAG) described previously.7 These data were segmented for analysis using the Cirrus Review Software package. The retinal pigment epithelium (RPE) and inner limiting membrane (ILM) algorithms were applied to generate en face images.
In this study we present OCTA findings of a patient with an acute CRAO, a disease process previously characterized and followed by observing structural changes on fundus photos, FA, and OCT.8,9 Use of OCTA has already been described in a variety of diseases, including age-related macular degeneration, branch retinal vein occlusion (BRVO), glaucoma, and retinal angiomatous proliferation.10–13 As suggested, OCTA was found to enhance visualization of deeper vascular layers and radial peripapillary network of the retina in healthy individuals when compared to FA.14 Quantitative values of choroidal neovascularization have also been determined using this technique, suggesting this information may act as an early indicator in disease progression or treatment response.10 Further expanding the scope of this technique, OCTA has also been applied to image microvascular responses in the iris of rodents.15 The accuracy and benefits of the technique have been supported using many different methodologies. For example, blood flow on OCTA was found to correspond with pattern stimulation of the retina,16 to the pattern standard deviation of visual field loss,11 and to expected hyperoxic response of retinal blood vessels.17
The benefit of OCT in CRAO is apparent, providing information of both inner and outer retinal layers. In addition, its use has been implicated in CRAO staging, a categorization shown to correlate with visual outcomes and treatment decisions.18 Evidence also supports the importance of choroidal perfusion on prognosis, information not visible on FA.18
Important prognostic factors of CRAO include the location of the occlusion and the presence of remaining blood flow, further proposing the benefits of OCTA following this type of pathology.18,19 Evidence also suggests that patients with CRAO are at an increased risk for ocular neovascularization; as such, close follow-up of the retinal vasculature is recommended.20
Our study is limited in relation to visual prognosis, as the patient was not followed over time with serial OCTAs. Previous studies have revealed little correlation between imaging in the acute phase and visual potential; following the progression of the CRAO proved more beneficial.21
This study supports the use of OCTA in the diagnosis and monitoring of CRAO. Future research is warranted to recognize the full potential of this imaging modality.
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- Wang Y, Fawzi AA, Varma R, et al. Pilot study of optical coherence tomography measurement of retinal blood flow in retinal and optic nerve diseases. Invest Ophthalmol Vis Sci. 2011;52(2):840–845. doi:10.1167/iovs.10-5985 [CrossRef]
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- Jia Y, Bailey ST, Wilson DJ, et al. Quantitative optical coherence tomography angiography of choroidal neovascularization in age-related macular degeneration. Ophthalmology. 2014;121(7):1435–1444. doi:10.1016/j.ophtha.2014.01.034 [CrossRef]
- Jia Y, Wei E, Wang X, et al. Optical coherence tomography angiography of optic disc perfusion in glaucoma. Ophthalmology. 2014;121(7):1322–1332. doi:10.1016/j.ophtha.2014.01.021 [CrossRef]
- Kuehlewein L, An L, Durbin MK, Sadda SR. Imaging areas of retinal nonperfusion in ischemic branch retinal vein occlusion with swept-source OCT microangiography. Ophthalmic Surg Lasers Imaging Retina. 2015;46(2):249–252. doi:10.3928/23258160-20150213-19 [CrossRef]
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- Pechauer AD, Jia Y, Liu L, Gao SS, Jiang C, Huang D. Optical coherence tomography angiography of peripapillary retinal blood flow response to hyperoxia. Invest Ophthalmol Vis Sci. 2015;56(5):3287–3291. doi:10.1167/iovs.15-16655 [CrossRef]
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