Ultrahigh Resolution Optical Coherence Tomography of the Monkey Fovea. Identification of Retinal Sublayers by Correlation With Semithin Histology Sections

Abstract

Abstract: : Purpose: Identification of unprecedented sequence of intra- and subretinal sublayers in the monkey retina using ultrahigh resolution optical coherence tomography (OCT) and precise correlation with corresponding semithin histological sections. Methods: Ultrahigh resolution OCT cross-sectional images with 1,4 µm axial x 3 µm transverse resolution were acquired from perfusion-fixed eye cups of Macaca fascicularis. After embedding serial semithin sections, including papilla and fovea, were obtained along OCT transsects. Nonlinear tissue shrinkage due to dehydration and sectioning stress limits direct overlay of features identified in histological sections onto corresponding OCT locations. Therefore misalignment was further corrected by using polygonal spline morphing based on corresponding unequivocal landmarks (papilla, foveal floor, pigment epithelium, inner limiting membrane). Results: The geometric normalization allows detailed comparison of both profiles as well as of data from published foveal images. Little correction occurring in the proximal part of the section suggests that ultrahigh resolution OCT signal bands correspond well to the main retinal layers of standard histology. However, misalignments occur at photoreceptor inner/outer segment level due to increased shrinkage ratios in unprocessed micrographs. These distortions were well compensated by the morphing procedure thus eliminating a major source of ambiguity. Conclusions: Adaptive geometric correction of corresponding sections allows more precise identification of features in retinal ultrahigh OCT imaging, even along the changing profiles of foveal sublayers. This correlation will allow extracting structural information of high clinical relevance in in vivo ultrahigh resolution ophthalmic OCT tomograms.

Keywords: retina • imaging methods (CT, FA, ICG, MRI, OCT, RTA, S • macula/fovea