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. 2013 Oct 18;4(11):2527-39.
doi: 10.1364/BOE.4.002527. eCollection 2013.

In vivo imaging of retinal pigment epithelium cells in age related macular degeneration

Ethan A Rossi  1 , Piero Rangel-Fonseca, Keith Parkins, William Fischer, Lisa R Latchney, Margaret A Folwell, David R Williams, Alfredo Dubra, Mina M Chung
Affiliations

In vivo imaging of retinal pigment epithelium cells in age related macular degeneration

Ethan A Rossi et al. Biomed Opt Express. .

Abstract

Morgan and colleagues demonstrated that the RPE cell mosaic can be resolved in the living human eye non-invasively by imaging the short-wavelength autofluorescence using an adaptive optics (AO) ophthalmoscope. This method, based on the assumption that all subjects have the same longitudinal chromatic aberration (LCA) correction, has proved difficult to use in diseased eyes, and in particular those affected by age-related macular degeneration (AMD). In this work, we improve Morgan's method by accounting for chromatic aberration variations by optimizing the confocal aperture axial and transverse placement through an automated iterative maximization of image intensity. The increase in image intensity after algorithmic aperture placement varied depending upon patient and aperture position prior to optimization but increases as large as a factor of 10 were observed. When using a confocal aperture of 3.4 Airy disks in diameter, images were obtained using retinal radiant exposures of less than 2.44 J/cm(2), which is ~22 times below the current ANSI maximum permissible exposure. RPE cell morphologies that were strikingly similar to those seen in postmortem histological studies were observed in AMD eyes, even in areas where the pattern of fluorescence appeared normal in commercial fundus autofluorescence (FAF) images. This new method can be used to study RPE morphology in AMD and other diseases, providing a powerful tool for understanding disease pathogenesis and progression, and offering a new means to assess the efficacy of treatments designed to restore RPE health.

Keywords: (110.1080) Active or adaptive optics; (170.1610) Clinical applications; (170.3880) Medical and biological imaging; (170.4470) Ophthalmology; (330.5310) Vision - photoreceptors.

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Figures

Fig. 1
Fig. 1
Nelder-Mead algorithm validated on a model eye. The start (white x’s) and end positions (white o’s) for 20 random starting points are overlaid on the intensity profile of the focused spot; solid lines link start and end positions and do not represent the algorithm path. Panels (a)-(c) show different views of the same data sliced at the maximum intensity position, showing coronal (a), side (b) and overhead (c) views. Note the difference in scale between the (x,y) and (z) dimensions. Color bar shows relation between color and normalized intensity.
Fig. 2
Fig. 2
Wide field FAF cSLO images and FAOSLO image locations. Images for subjects AMD1, AMD2, normal young healthy control & AMD3 are shown in panels (a), (b), (c), & (d), respectively. FAOSLO image locations shown in subsequent figures are outlined in yellow. Scale bar is 400 µm.
Fig. 3
Fig. 3
Fluorescence adaptive optics images of the RPE mosaic at locations marked in Fig. 2 for (a) AMD1-1 (b) AMD1-2 (c) AMD2-1 (d) AMD2-2 (e) AMD3-1, and (f) normal young control-1. Scale bar is 50 µm.
Fig. 4
Fig. 4
Segmented RPE cells from FAOSLO images shown in Fig. 3. (a) AMD1-1 (b) AMD1-2 (c) AMD2-1 (d) AMD2-2 (e) AMD3-1, and (f) normal young control-1. Scale bar is 50 µm.
Fig. 5
Fig. 5
Despite fairly uniform FAF in cSLO, RPE mosaic imaged in AOSLO shows deviation from normal morphology. (a) Location 2 from AMD2 in FAOSLO (from Fig. 4(c)), compared to corresponding area imaged in FAF cSLO Spectralis, where some structure can be seen, but individual cells are not resolved, contrast has been stretched in (b) for comparison to AOSLO and original FAF image without contrast adjustment. Scale bar is 50 µm.
Fig. 6
Fig. 6
AMD eyes show greater variance in cell area. Segmented cells colored by area for: (a) AMD1-1, (b) AMD1-2, (c) AMD2-1, (d) AMD2-2, (e) AMD3-1, (f) normal young control-1 and (g) normal young control-2. Color bar shows relation between color and area. Below each image is the corresponding histogram of cell sizes. Note the difference in number of cells for each image (y-axis of each histogram); bin sizes are identical. Normal eyes show a tight, fairly normal distribution of sizes (histograms below (f) and (g)), while the AMD eyes (histograms below a-e) show larger variance, with both larger and smaller cells.
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