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J. I. W. Morgan, D. C. Gray, R. Wolfe, B. Masella, A. Dubra, D. R. Williams; Imaging Individual Human Retinal Pigment Epithelium Cells in vivo. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1953.
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© ARVO (1962-2015); The Authors (2016-present)
The retinal pigment epithelium (RPE) cells are responsible for providing metabolic support to the photoreceptors, helping in the regeneration of retinal in the visual cycle, and phagocytosing the photoreceptor outer segments. Lipofuscin accumulates in the RPE cell cytoplasm as a natural byproduct of these processes. Recently, in vivo techniques have been developed to image the RPE layer by detecting lipofuscin autofluorescence in a scanning laser ophthalmoscope (SLO). Here we combine non-invasive autofluorescence SLO imaging techniques with high-resolution adaptive optics (AO) to image individual human retinal pigment epithelium cells in vivo.
Normal subjects were dilated, cyclopleged and asked to fixate at a point in space. Subjects were stabilized with use of a bite bar. The retina was imaged simultaneously with two light channels in an AOSLO equipped with fluorescence imaging capabilities; one channel was used for reflectance imaging of the cone photoreceptors while the other channel simultaneously detected the RPE autofluorescence. 568nm light was used for lipofuscin autofluorescence excitation and the emission was detected with a 40nm bandpass filter centered at 624nm. The high contrast reflectance frames were registered to determine the relative shifts caused by eye motion. This motion was applied to the simultaneous low signal autofluorescence frames and the frames were averaged to give the final autofluorescence image of the RPE.
Individual RPE cells were resolved in vivo using this method. The RPE mosaic was imaged at different eccentricities in the peripheral retina. RPE cell density decreased and RPE cell size and spacing increased as eccentricity from the fovea increased. The ratio of cones to RPE cells decreases as a function of eccentricity. Repeat measurements of the same retinal location 50 days later show the same RPE cells and distribution.
We have imaged individual RPE cells in human retina in vivo. This non-invasive method allows the morphology of the RPE in normal and diseased retina to be studied in vivo. Additionally, this technique will allow longitudinal studies for tracking disease progression and assessing treatment efficacy in human patients and animal models of retinal diseases affecting the RPE.
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