Re: Staurenghi et al.: Proposed lexicon for anatomic landmarks in normal posterior segment spectral-domain optical coherence tomography: the IN•OCT consensus (Ophthalmology 2014;121:1572-8)

Visible Light Optical Coherence Tomography (OCT) Quantifies Subcellular Contributions to Outer Retinal Band 4

Purpose

To use visible light optical coherence tomography (OCT) to investigate subcellular reflectivity contributions to the outermost (4th) of the retinal hyperreflective bands visualized by current clinical near-infrared (NIR) OCT.

Methods

Visible light OCT, with 1.0 µm axial resolution, was performed in 28 eyes of 19 human subjects (21–57 years old) without history of ocular pathology. Two foveal and three extrafoveal hyperreflective zones were consistently depicted within band 4 in all eyes. The two outermost hyperreflective bands, occasionally visualized by NIR OCT, were presumed to be the retinal pigment epithelium (RPE) and Bruch's membrane (BM). RPE thickness, BM thickness, and RPE interior reflectivity were quantified topographically across the macula.

Results

A method for correcting RPE multiple scattering tails was found to both improve the Gaussian goodness-of-fit for the BM intensity profile and reduce the coefficient of variation of BM thickness in vivo. No major topographical differences in macular BM thickness were noted. RPE thickness decreased with increasing eccentricity. Visible light OCT signal intensity in the RPE was weighted to the apical side and attenuated more across the RPE in the fovea than peripherally.

Conclusions

Morphometry of the presumed RPE and BM bands is consistent with known anatomy. Weighting of RPE reflectivity toward the apical side suggests that melanosomes are the predominant contributors to RPE backscattering and signal attenuation in young eyes.

Translational Relevance

By enabling morphometric analysis of the RPE and BM, visible light OCT deciphers the main reflectivity contributions to outer retinal band 4, commonly visualized by commercial OCT systems.

Central retinal preservation in rdAc cats

OBJECTIVE

Children with Leber congenital amaurosis (LCA) due to CEP290 mutations show characteristic macular preservation. Spectral domain-optical coherence tomography (SD-OCT) is a noninvasive technique to investigate retinal structural changes. Loss of integrity of the ellipsoid zone (EZ) on OCT in people with retinal disease has been associated with loss of visual function and is a useful measure of retinal disease progression. We hypothesized that rdAc felines with Cep290 mutation would have a similar pattern of degeneration, with relative central retinal preservation associated with maintenance of the EZ.

PROCEDURES

Fundus imaging, confocal scanning laser ophthalmoscopy, and SD-OCT cross-sectional imaging was performed on 11 rdAc cats ranging from 6 months to 10 years of age. Images were collected from the area centralis, visual streak, and the mid-superior and mid-inferior retina. Receptor plus (REC+, encompassing the entire length of photoreceptors) thicknesses were measured. Regional rates of degeneration were determined by regression analysis and compared using unpaired t-tests. The EZ was evaluated for the presence, absence, or loss of definition.

RESULTS

RdAc cats showed REC+ thinning over time in all regions. The area centralis and visual streak had a slower rate of thinning than the mid-peripheral retina. There was loss of integrity of the EZ initially in the more peripheral regions, while its integrity was maintained in the area centralis and visual streak at all ages studied.

CONCLUSIONS

rdAc cats show preservation of the central retina with maintenance of EZ integrity, which recapitulates findings in human patients.

ASSESSING PHOTORECEPTOR STRUCTURE ASSOCIATED WITH ELLIPSOID ZONE DISRUPTIONS VISUALIZED WITH OPTICAL COHERENCE TOMOGRAPHY

PURPOSE

To compare images of photoreceptor layer disruptions obtained with optical coherence tomography (OCT) and adaptive optics scanning light ophthalmoscopy (AOSLO) in a variety of pathologic states.

METHODS

Five subjects with photoreceptor ellipsoid zone disruption as per OCT and clinical diagnoses of closed-globe blunt ocular trauma (n = 2), macular telangiectasia type 2 (n = 1), blue-cone monochromacy (n = 1), or cone-rod dystrophy (n = 1) were included. Images were acquired within and around photoreceptor lesions using spectral domain OCT, confocal AOSLO, and split-detector AOSLO.

RESULTS

There were substantial differences in the extent and appearance of the photoreceptor mosaic as revealed by confocal AOSLO, split-detector AOSLO, and spectral domain OCT en face view of the ellipsoid zone.

CONCLUSION

Clinically available spectral domain OCT, viewed en face or as B-scan, may lead to misinterpretation of photoreceptor anatomy in a variety of diseases and injuries. This was demonstrated using split-detector AOSLO to reveal substantial populations of photoreceptors in areas of no, low, or ambiguous ellipsoid zone reflectivity with en face OCT and confocal AOSLO. Although it is unclear if these photoreceptors are functional, their presence offers hope for therapeutic strategies aimed at preserving or restoring photoreceptor function.