Non-Invasive Detection of Early Retinal Neuronal Degeneration by Ultrahigh Resolution Optical Coherence Tomography

Abstract

Optical coherence tomography (OCT) has revolutionises the diagnosis of retinal disease based on the detection of microscopic rather than subcellular changes in retinal anatomy. However, currently the technique is limited to the detection of microscopic rather than subcellular changes in retinal anatomy. However, coherence based imaging is extremely sensitive to both changes in optical contrast and cellular events at the micrometer scale, and can generate subtle changes in the spectral content of the OCT image. Here we test the hypothesis that OCT image speckle (image texture) contains information regarding otherwise unresolvable features such as organelle changes arising in the early stages of neuronal degeneration. Using ultrahigh resolution (UHR) OCT imaging at 800 nm (spectral width 140 nm) we developed a robust method of OCT image analyses, based on spatial wavelet and texture-based parameterisation of the image speckle pattern. For the first time we show that this approach allows the non-invasive detection and quantification of early apoptotic changes in neurons within 30 min of neuronal trauma sufficient to result in apoptosis. We show a positive correlation between immunofluorescent labelling of mitochondria (a potential source of changes in cellular optical contrast) with changes in the texture of the OCT images of cultured neurons. Moreover, similar changes in optical contrast were also seen in the retinal ganglion cell- inner plexiform layer in retinal explants following optic nerve transection. The optical clarity of the explants was maintained throughout in the absence of histologically detectable change. Our data suggest that UHR OCT can be used for the non-invasive quantitative assessment of neuronal health, with a particular application to the assessment of early retinal disease.

Characterization of Inner Retinal Spots With Inverted Reflectivity on En Face Optical Coherence Tomography in Diabetic Retinopathy

“…Several basic and clinical research reports have supported cellular damage in ganglion cells in DR. [19][20][21][22][23] During the process of cell death, the reflective properties were modulated by changes in the organelles, which might be compatible with the reflectivity levels of the NFL and GCL seen in the current OCT findings. 29,30 Another possibility is that spots with inverted reflectivity correspond to the gliotic mass after neurodegenerative changes in the ganglion cells, regardless of whether the glial cells are derived from astrocytes or Müller cells. Several .…”

The optical detection of retinal ganglion cell damage

“…We therefore constructed a custom OCT coupled to a standard compound microscope to examine changes in texture that occur in both cultured RGCs and retinal explants 30 (Figure 3b). The OCT used a Femtosecond Integral Ti:sapphire laser with a high bandwidth of 140 nm to provide a theoretical bandwidth of 3mm.…”

“…Histological examination confirmed mitochondrial aggregation and caspase activation in RGC5 cell death following the initiation of apoptosis by the addition of staurosporine. 30,32 The details of the mathematical modeling are described in details elsewhere. 30 In brief, the image was parameterized using 65 features, which were then selected on the basis of the accuracy with which they correlated with culture stage.…”

“…30,32 The details of the mathematical modeling are described in details elsewhere. 30 In brief, the image was parameterized using 65 features, which were then selected on the basis of the accuracy with which they correlated with culture stage. The selection of these dimensions was hypothesis free and based on the (unprocessed) spectral signal from the OCT.…”

Adaptive-weighted bilateral filtering and other pre-processing techniques for optical coherence tomography

“…Optical Coherence Tomography (OCT) has recently become a powerful tool in medicine, particularly in the diagnosis and monitoring of retinal damage in a range of diseases [1,2]. It provides high-resolution cross-sectional images of biological tissues using noninvasive imaging technology.…”