Enabling technologies for functional optical coherence tomography in retinal disease

Abstract

Optical coherence tomography (OCT) imaging of retinal function has become increasingly important because alterations in the function may reflect earlier changes in ocular diseases than the alterations in the structure. Since diagnostic markers in structural OCT using commercial instruments already underwent extensive investigations, novel markers in retinal function implying disease onset or progression are important for further development of novel markers in OCT diagnostics of ocular disease. Retinal OCT applications such as blood flow imaging and stimulus-response imaging often requires high imaging speed since repeated scans of the same position or densely sampled scans are used. Our group developed a high-speed swept-source/Fourier-domain OCT (SS-OCT) prototype to investigate retinal hemodynamics and vascular structures in major ocular diseases such as age-related macular degeneration (AMD), glaucoma, and diabetic retinopathy with OCT angiography or Doppler OCT.

Our group also used an ultrahigh-resolution (UHR) spectral/Fourier-domain OCT (SD-OCT) instrument to investigate dark adaptation of the photoreceptors after a photobleach by measuring the changes in the distances between densely packed, bright bands in the outer retina. Dark adaptation can be an indicator of photoreceptor health and it is postulated that compromised dark adaptation is a manifestation of early AMD. The current thesis reports two technical advancements in OCT imaging of retinal function: image processing algorithm for total retinal blood flow (TRBF) calculation with en face Doppler OCT using the high-speed SS-OCT prototype and the instrumentation of the newly deployed UHR SD-OCT prototype with effective depth range extension using reference arm length modulation (ReALM). These techniques aim for operator-friendly, robust, and repeatable assessment of retinal blood flow or the photoreceptor layer to provide powerful tools for future investigations of retinal function.

The contents of the current thesis includes hardware and software approaches that overcomes inherent limitations of OCT such as signal penetration and depth range as well as preliminary imaging results and pilot study findings.