Peter Gehlbach, MD, PhD, a professor of ophthalmology in the retina division at Wilmer Eye Institute of the Johns Hopkins University School of Medicine in Baltimore, Maryland, has clinical interest in Vasoptic Medical’s XyCAM RI retinal imager because it fills an unmet imaging need. Specifically, the device provides the ability to dynamically observe microvascular flow repeatedly, over time, with no dye required.

“Many ophthalmic diseases have vascular etiologies or vascular symptoms which present an important avenue for screening, diagnostics, and monitoring disease status,” says Abhishek Rege, PhD, founder and president of Vasoptic Medical. “Early changes associated with disease pathology may be marked by subtle changes in blood flow before paving their way to gross morphologic or anatomic changes that appear on static photographs.”

Although current ophthalmic imaging systems have undoubtedly made huge strides in obtaining anatomical information at a high en-face spatial resolution, they lack the ability to image function or blood flow, Dr. Rege continues. The gold standard for imaging perfusion is fluorescein angiography, which relies on intravenous dye injection. OCT angiography, which is rapidly being adopted over invasive angiography, achieves time-aggregated maps of perfused vasculature but isn’t able to obtain blood flow information.

HOW IT WORKS

The XyCAM RI uses laser speckle contrast imaging to noninvasively obtain blood flow information. It does this via low intensity laser illumination to induce speckle patterns in images captured by the camera, Dr. Gehlbach explains. Motion of the blood induces blurring in the speckle and is proportional to blood flow that is localizable to vessels. A map of the blurring shows how blood flows, which can be followed over time.

Obtained at 82 frames per second, the XyCAM RI data reveal blood flow pulsations associated with a cardiac cycle. “This feature is complementary to the capabilities of other commercially available ophthalmic imaging techniques and completes the picture regarding retinal vascular status,” Dr. Rege says. “It further permits clinicians to interpret retinal findings in conjunction with vascular status and blood flow, which may be central to the pathology or help dissect confounding observations.”

The XyCAM RI resolves retinal blood flow information in a 25-degree circular field of view over 1200 x 1200 pixels revealing blood flow in retinal arterioles and venules as small as 30 µm in diameter. Imaging can be done nonmydriatically.

Imaging workflow is similar to fundus photography; image acquisition can be triggered by the click of a button. The XyCAM RI provides multiple visualizations of the retina — a colored blood flow visualization mode with an adjustable color scale, a dye-free angiogram mode wherein perfused vessels can be visualized with high contrast, and a reconstructed fundus image mode that provides vascular morphology with monochrome high contrast, Dr. Rege says. The XyCAM RI also displays reference data from an optional pulse oximeter available with the system.

CLINICAL APPLICATIONS

Blood flow and vascular characteristics are altered in a variety of clinical conditions including diabetic retinopathy, retinal arterial and vein occlusions, retinopathy of prematurity, hypertensive retinopathy, Purtscher’s retinopathy, and glaucoma, as well as other diseases such as sickle cell disease, pre-eclampsia/eclampsia of pregnancy, migraine, giant cell arteritis, and vascular drug response, Dr. Gehlbach says.

Many medications and other therapeutics used in treatment influence blood flow as a primary target. Alterations in blood flow may be an undesirable side effect in some cases. In any of these situations, the XyCAM RI provides retina specialists with insights about blood flow status in various vessels and regions of the retina at both aggregate and reductionist levels. “Such knowledge is important for more specific diagnostics, routine monitoring, and a personalized approach to treatment,” Dr. Rege says.

Specifically, Dr. Gehlbach says blood flow data may affect personalized drug dosing and drug combination treatment regimens, and may determine when treatment can be stopped. It may be used to establish noninferiority of vasoactive drugs allowing for cost savings and the evaluation of various drug forms including generics. Flow information may also be used as a sensor for noninvasively assessing perfusion of tissues during surgical procedures. It may identify safety concerns related to previously unknown vasoactivity of established and new drugs.

PATIENT BENEFITS

Patients perceive the near infrared illumination of the XyCAM RI as mild; it doesn’t require dilation or cause discomfort, Dr. Rege says. Fixation targets assist patients in keeping their gaze steady for imaging.

Not having to use dye such as fluorescein or indocyanine green means that venous access isn’t needed. Furthermore, dyes have inherent toxicities, and some patients have severe allergic responses, Dr. Gehlbach says. Because dyes stain tissue, they prevent repeat testing until after a lengthy clearance period — preventing further assessment of blood-flow dynamics.

Other advantages over dye-based angiographic techniques include XyCAM’s ability to reveal blood-flow dynamics as opposed to merely revealing perfused vessels and leaks. Noninvasive techniques also simplify imaging workflows, which in turn leads to reduced costs associated with dyes and personnel time. This provides a greater ability to repeat the procedure on the same or a different region of the retina in one or both eyes, Dr. Rege says.

Perhaps more important than these conveniences, Dr. Rege says the XyCAM RI permits the retina specialist to obtain more information about a patient’s health status and therefore can provide a more informed assessment and treatment plan that will benefit the patient.

OTHER USES

The XyCAM RI has benefits beyond a clinician’s practice. The device opens a new dimension for clinicians interested in clinical research on disease management applications as well as basic research on disease pathophysiology, Dr. Rege says. XyCAM RI offers a mode of operation in which data can be stored and tracked based on study identifiers rather than personally identifiable information. Results of data analysis can also be exported to research-friendly platforms such as Microsoft Excel for tabulation and statistical analysis. RP