Correlation of spectral domain optical coherence tomography with histology and electron microscopy in the porcine retina

Abstract

Spectral domain optical coherence tomography (SD-OCT) is used as a non-invasive tool for retinal morphological assessment in vivo. Information on the correlation of SD-OCT with retinal histology in the porcine retina, a model resembling the human retina, is limited. Herein, we correlated the hypo- and hyper-reflective bands on SD-OCT with histology of the lamellar architecture and cellular constituents of the porcine retina. SD-OCT images were acquired with the Heidelberg Spectralis HRA + OCT. Histological analysis was performed using epoxy resin embedded tissue and transmission electron microscopy. Photomicrographs from the histologic sections were linearly scaled to correct for tissue shrinkage and correlated with SD-OCT images. SD-OCT images correlated well with histomorphometric data. A hyper-reflective band in the mid-to-outer inner nuclear layer correlated with the presence of abundant mitochondria in horizontal cell processes and adjacent bipolar cells. A concentration of cone nuclei corresponded to a relative hypo-reflective band in the outer portion of the outer nuclear layer. The presence of 3 hyper-reflective bands in the outer retina corresponded to: 1) the external limiting membrane; 2) the cone and rod ellipsoid zones; and 3) the interdigitation zone of photoreceptor outer segments/retinal pigment epithelium (RPE) apical cell processes and the RPE. These correlative and normative SD-OCT data may be employed to characterize and assess the in vivo histologic changes in retinal vascular and degenerative diseases and the responses to novel therapeutic interventions in this large animal model.

Data on SD-OCT image acquisition, ultrastructural features, and horizontal tissue shrinkage in the porcine retina

“…The Heidelberg Spectralis HRA+OCT with the software Heidelberg Eye Explorer (HEYEX version 6.6, Heidelberg, Germany) was employed to image the retina along the vertical meridian through the optic nerve head as described in Xie et al [2] . Signal quality was at least 25 db, and 100 frames were averaged per B-scan.…”

Long distance retrograde degeneration of the retino-geniculo-cortical pathway in homonymous hemianopia

“…To assess changes in retinal thickness over time, we performed spectral-domain optical coherence tomography (OCT) (Cirrus HD-OCT model, Carl Zeiss Meditec, Dublin, CA, USA). Because age-related OCT thinning is relatively modest, at 1 µm of GCC or 2 µm of RNFL every decade [24, 25], the changes we measure over time likely reflected changes corresponding to the homonymous visual field defect. We performed the Macular Cube 512 x 128 and the Optic Disc 200 x 200 scans per manufacturer’s instructions.…”

“…Advances in optical coherence tomography (OCT) means that we now have a reliable in vivo method of measuring long-distance, retrograde degeneration of the visual pathway in humans at point-of-care locations such as the eye clinic [22, 23]. Commercial spectral-domain OCT machines provide resolution of 3-5 microns, which allow for quantification of individual retinal layers comparable to that of retinal histology [24, 25]. Advances in OCT segmentation means we can routinely segment the thickness of the layer containing retinal ganglion cells (ganglion cell layer or GCC) and the thickness of the layer containing unmyelinated retinal ganglion cell axons (retinal nerve fiber layer or RNFL).…”

Etching-enabled extreme miniaturization of graded-index fiber-based optical coherence tomography probes

“…Both porcine retina B-scans reveal a hyper-reflective zone at the back of the retina that can be linked to the ellipsoid zones of cones and rods and the interdigitation zone/retinal pigment epithelium complex. 17 Nevertheless, individual layers cannot be clearly identified within the hyperreflective zone. The use of the miniaturized probes with application-tailored OCT setups/machines as well as the use of averaging and signal processing strategies can facilitate applications demanding high imaging resolution.…”