Intravenous thrombolysis may be an effective therapeutic option for the treatment of central retinal artery occlusion (CRAO); however, no imaging modalities have been established to assess retinal viability, explains a systematic review published in the Journal of Stroke and Cerebrovascular Diseases. The research shows existing and experimental imaging techniques which may be useful in the treatment of CRAO.
The retina comprises a dual circulation anatomy, in which the inner retinal vascular supply is received from the central retinal artery and the outer retinal choroid from the posterior ciliary circulation. Recent evidence suggests retinal tissue may be rescued within 4.5 hours of CRAO with the restoration of blood flow. The resilience of the retinal tissue may be in part due to the dual circulation anatomy, allowing for passive diffusion of oxygen from the outer retina and choroid.
There are 3 standard imaging techniques for patients with CRAO (fluorescein angiography, fundus photography, and transorbital ultrasound). Optical coherence tomography (OCT) and retinal functional imaging are experimental procedures which have had intriguing results which may improve the treatment landscape for patients with CRAO.
The standard technique for confirming CRAO is fluorescein angiography, which can detect normal filling and circulation in the choroidal space and any delays in artery blood flow or arteriovenous transit time. Fundus photography can detect early symptoms of segmental blood flow and retinal artery non-perfusions and the late symptoms of retinal whitening or the cherry-red spot. Transorbital ultrasound detects the ‘spot sign’ and depleted blood flow in the central retinal artery.
OCT is noninvasive using low-coherence light and provides 3-dimensional images of tissues 22 mm in depth at a resolution of 1 µm to 10 μm. The technique has primarily been used to measure structure thicknesses in the retina. In the setting of CRAO, the changes of optical intestines in the retinal layers can be detected. For this imaging modality to be useful for assessing retinal viability, biomarkers for altered retinal anatomy are still required.
Retinal functional imaging is a noninvasive procedure which allows for functional and structural examination. It has a similar resolution as OCT but with a larger field of view. This imaging modality creates 4 detailed outputs which feature capillary perfusion maps, blood flow velocity, retinal oxygenation, and retinal metabolic function. This tool has been used for assessing blood flow among patients with retinitis pigmentosa, diabetic retinopathy, and multiple sclerosis. Currently, there have been no studies published in the CRAO setting.
The researchers conclude that the treatment of acute stroke has been transformed by multimodal imaging tools. There is hope that analogous techniques may have a similar effect on the treatment of CRAO. There are currently no validated modalities which provide rapid and accurate data about the viability of retinal tissues. Both OCT and retinal functional imaging, with additional study, have potential to advance the care landscape for patients with CRAO by allowing clinicians to determine whether retinal tissues remain viable and may be viable candidates for intravenous thrombolysis.
Mac Grory B, Schrag M, Poli S, et al. Structural and functional imaging of the retina in central retinal artery occlusion-current approaches and future directions. J Stroke Cerebrovasc Dis. 2021;30(7):105828. doi:10.1016/j.jstrokecerebrovasdis.2021