High-speed adaptive optics line-scan OCT for cellular-resolution optoretinography

Abstract

Optoretinography–the non-invasive, optical imaging of light-induced functional activity in the retina–stands to provide a critical biomarker for testing the safety and efficacy of new therapies as well as their rapid translation to the clinic. Optical phase change in response to light, as readily accessible in phase-resolved OCT, offers a path towards all-optical imaging of retinal function. However, typical human eye motion adversely affects phase stability. In addition, recording fast light-induced retinal events necessitates high-speed acquisition. Here, we introduce a high-speed line-scan spectral domain OCT with adaptive optics (AO), aimed at volumetric imaging and phase-resolved acquisition of retinal responses to light. By virtue of parallel acquisition of an entire retinal cross-section (B-scan) in a single high-speed camera frame, depth-resolved tomograms at speeds up to 16 kHz were achieved with high sensitivity and phase stability. To optimize spectral and spatial resolution, an anamorphic detection paradigm was introduced, enabling improved light collection efficiency and signal roll-off compared to traditional methods. The benefits in speed, resolution and sensitivity were exemplified in imaging nanometer-millisecond scale light-induced optical path length changes in cone photoreceptor outer segments. With 660 nm stimuli, individual cone responses readily segregated into three clusters, corresponding to long, middle, and short-wavelength cones. Recording such optoretinograms on spatial scales ranging from individual cones, to 100 µm-wide retinal patches offers a robust and sensitive biomarker for cone function in health and disease.

Super-resolution ophthalmoscopy: Virtually structured detection for resolution improvement in retinal imaging

“…The high-speed and super-resolution imaging with single photoreceptor resolution also promises a feasible solution to advance functional intrinsic optical signal (IOS) imaging, 31,32 also termed as optophysiology 33 or optoretinography (ORG), 34–36 for objective assessment of retinal physiology. It is known that eye diseases, such as age-related macular degeneration (AMD), 37–39 retinitis pigmentosa (RP), 40,41 diabetic retinopathy (DR), 42,43 can cause photoreceptor dysfunctions.…”

Reflective mirror-based line-scan adaptive optics OCT

“…An anamorphic configuration consisting of two-cylinder lens achromats (CL3 and CL4 in Fig.1) was applied to optimize the spectral and spatial resolution, and to improve light collection efficiency. The principle behind its operation is elaborated in Pandiyan et al [16]. This configuration provided an asymmetric beam magnification such that following pupil (P6) and retinal (R6 – R8) planes were scaled by the ratio of the focal lengths of CL3 and CL4.…”

“…With AO, Zhang et al [6] made the first observations of the interface between the inner and outer segments of individual cones in retinal B-scans, though the low B-scan rate of 500 Hz impeded volumetric imaging. Pandiyan et al [16] presented the first volumetric, high-speed line-scan spectral domain OCT with hardware AO, aimed at phase-resolved acquisition of light-induced retinal activity or optoretinography.…”

“…In line-scan AO-OCT, a cylindrical lens generates a linear illumination at the entrance pupil of the system, that is then optically conjugated with a 1-D galvo scanner, a deformable mirror and the eye’s pupil using afocal telescopes. In Pandiyan et al, [16] achromatic lens-based telescopes were used for the ease of alignment and an abundant commercial availability of effective focal lengths. However, lens back-reflections are a common issue that are removed by tipping and tilting the lenses, which in turn leads to optical aberrations.…”

Toward a clinical optoretinogram: a review of noninvasive, optical tests of retinal neural function

“…The sweep rate of FF-SS-OCT systems is orders of magnitude lower than that of scanning SS-OCT systems, which amplifies the effects of disturbances to the interferometer due to system vibrations, air currents, or eye movements, and this may place an additional limitation on FF-SS-OCT sensitivity. Pandiyan et al developed a novel line-scanning AO-OCT system to try to combine benefits of both SD-OCT and FF-SS-OCT (125). In their approach, the retina is illuminated with a line of broadband light, which is imaged onto a 2D sensor through a diffraction grating, such that one dimension on the sensor corresponds to spatial extent (along the line) and the other to wavelength, as the light is dispersed by the grating.…”