Adaptive optics optical coherence tomography angiography in healthy volunteers and patients

Abstract

Purpose : To investigate the benefits of adaptive optics (AO) technology for optical coherence tomography angiography (OCTA) in healthy volunteers and patients.

Methods : For this study we used an AO-OCT system with a compact design. Correction is achieved with a guide star, a Shack-Hartman wave front sensor and a deformable mirror. The AO-OCT covers a field of view of 2°x2° and is operated at 840nm with 200kHz A-scan rate. The axial resolution within the retina is ~5µm. The transverse diffraction limited resolution is ~4µm. To achieve motion contrast four B-scans are acquired at the same sample location. The instrument was tested in healthy volunteers and in patients with diabetic retinopathy (DR) and Stargardt disease. For a comparison with state of the art OCTA systems, images were also recorded with commercial devices.

Results : Projections artefacts and limited transverse resolution in OCTA represent challenges for accessing the true extension of capillaries and for distinguishing between the different capillary plexuses. Improved contrast for retinal vessels could already be observed in AO-OCT intensity images. AO-OCTA data showed quantitative and qualitative higher contrast than AO-OCT intensity images. In comparison with standard OCTA the transverse resolution is greatly improved (Fig.1 A,B). This allows assessing the true extension of retinal capillaries. In addition, projection artifacts are greatly suppressed using AO-OCTA. In patients with DR AO-OCTA showed improved contrast of feeding vessels of microaneurysm (green arrows Fig.1 C,D) and the visualization of a capillary loop that cannot be clearly seen in the intensity image (red arrows Fig.1 C,D). Recently vascular abnormalities in patients with Stargardt disease have been reported. Apart from the improved transverse resolution that enables to calculate a more accurate vessel density, the improved contrast allows to visualize capillaries embedded in the nerve fiver layer (blue arrow Fig.1 E,F).

Conclusions : The higher numerical aperture associated with AO-OCT greatly reduces projection artifacts in angiographic data. This allows a clearer separation between different vascular beds. Using AO-OCTA the contrast of vessels is improved. Results in patients emphasize the potential of this technique to visualize capillaries embedded in highly scattering media. AO-OCTA may represent a valuable tool for monitoring the progression of vasculature changes.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.