Spectral domain optical coherence tomography and adaptive optics: imaging photoreceptor layer morphology to interpret preclinical phenotypes

Abstract

Recent years have seen the emergence of advances in imaging technology that enable in vivo evaluation of the living retina. Two of the more promising techniques, spectral domain optical coherence tomography (SD-OCT) and adaptive optics (AO) fundus imaging provide complementary views of the retinal tissue. SD-OCT devices have high axial resolution, allowing assessment of retinal lamination, while the high lateral resolution of AO allows visualization of individual cells. The potential exists to use one modality to interpret results from the other. As a proof of concept, we examined the retina of a 32 year-old male, previously diagnosed with a red-green color vision defect. Previous AO imaging revealed numerous gaps throughout his cone mosaic, indicating that the structure of a subset of cones had been compromised. Whether the affected cells had completely degenerated or were simply morphologically deviant was not clear. Here an AO fundus camera was used to re-examine the retina (~6 years after initial exam) and SD-OCT to examine retinal lamination. The static nature of the cone mosaic disruption combined with the normal lamination on SD-OCT suggests that the affected cones are likely still present.

Fig. 35.1

Processing retinal images from the Medical College of Wisconsin Adaptive Optics Ophthalmoscope. (a) Raw image from the CCD camera (~1.8° × ~0.9°). (b) Noise image comprised of dust, beam profile, and CCD circuit. (c) Processed retinal image (noise removed, registered average of 20 individual frames)

Fig. 35.2

Longitudinal imaging of the cone mosaic in the LIAVA retina. (a) Cone mosaic image from 1.25° temporal retina, taken November 2008 on the Medical College of Wisconsin Adaptive Optics Ophthalmoscope. Scale bar = 20 microns (b) Same image as in (a), with cone locations identified as dots. (c) Comparison of cone locations in (b) (crosses) to that from the exact same retinal location taken about 6 years prior (open circles). (d) Plot of cone density as a function of eccentricity. Shaded region represents normal bounds from histology data (Curcio et al. 1990) and filled circles represent average ± 1 SD values from adaptive optics data (Carroll et al. 2005). Density data for patient NC is plotted as a black dashed line (November 2008) and a gray line (January 2003)

Fig. 35.3

SD-OCT imaging in the LIAVA retina. (a) Line scan through the central fovea of patient NC, main retinal layers are labeled: NFL nerve fiber layer, GCL layer, layer, = ganglion cell IPL = inner plexiform INL = inner nuclear = layer, OPL outer plexiform layer, ONL outer nuclear layer, ELM = external limiting membrane, IS/OS = = junction, = inner/outer segment RPE = retinal pigment epithelium. (b) ONL thickness across horizontal meridian in normal subjects (shaded gray, ±2 SD) and patient NC with LIAVA M-opsin (dashed black line). Thickness data is presented as right eye equivalents