Imaging method for ocular diseases uses new approach

Fort Lauderdale, FL-Quantitative in vivo assessment of retinal blood flow attained with ultra-high-speed swept source/Fourier-domain optical coherence tomography (OCT) could be beneficial for assessing pathologic changes in ocular diseases associated with abnormalities in retinal blood flow, such as glaucoma, age-related macular degeneration, and diabetic retinopathy.

Analysis of measurements taken in healthy eyes shows that the technique can measure absolute blood flow in single vessels and total retinal blood flow.

This new approach to measuring total retinal blood flow is based on a technique for cerebral blood flow measurement developed by V.J. Srinivasan et al., published in 2010 in Optics Express. It does not require measurement of the vessel angle because the flow is measured at a fixed angle of 0°, or in an en face plane, perpendicular to the optical beam.

At the 2011 meeting of the Association for Research in Vision and Ophthalmology, Bernhard Baumann, PhD, postdoctoral associate, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, discussed evaluation of a modified version of this measurement technique performed in the Research Laboratory of Electronics under the direction of principal investigator James G. Fujimoto, PhD, professor of electrical engineering. Dr. Baumann is also affiliated with the New England Eye Center, Tufts University School of Medicine, Boston.

Dr. Fujimoto and collaborators developed an ultra-high-speed swept source/Fourier-domain OCT based on a swept laser light source at 1,050 nm, operating at 200,000 axial scans per second, which is 5 to 10 times faster than commercial OCT systems.

To test the instrument's capabilities, both structural and volumetric imaging were performed. Dense three-dimensional OCT data sets of the optic disk region were recorded in healthy human retinas, and Doppler OCT images of retinal blood flow were calculated from these data sets. Doppler OCT is a functional extension of OCT that enables the measurement of flow velocities in OCT data sets. Doppler flow velocities were calculated between every other axial scan and between every scan, providing detection sensitivity in two velocity ranges.

Total flow was measured by extracting Doppler images in the en face plane and integrating over the vessel cross-sections. These total blood flow measurements were obtained without reconstruction of the vessels' angle or geometry by acquiring dense volumetric OCT images.

These methods require very high-speed imaging in order to acquire sufficient numbers of axial scans to construct an en face image.