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.
Highlights
Drusen and atrophy of the retinal pigment epithelium (RPE) are hallmarks of age related macular degeneration (AMD) [1,2,3]
The total absence of an fundus autofluorescence (FAF) signal is often interpreted as complete RPE atrophy; spectral domain optical coherence tomography (SD-OCT) has been shown to be more precise for measuring lesion size in geographic atrophy (GA) [14]
We developed the photochemical Rochester Exposure Limit (REL) based on previous data from Morgan et al that showed changes in monkey RPE AF after exposure to visible light levels below the American National Standards Institute (ANSI) limit [26,27]
Summary
Drusen and atrophy of the retinal pigment epithelium (RPE) are hallmarks of age related macular degeneration (AMD) [1,2,3]. Histological studies of postmortem eyes have shown that substantial changes occur in RPE cell mosaic morphology in AMD [4,5]. These changes may precede and/or accompany RPE cell death and the degeneration of overlying photoreceptors [4,6]. Clinical imaging methods, such as confocal scanning laser ophthalmoscopy (cSLO), are used to examine the FAF pattern as a means of assessing the health of the RPE in AMD and other retinal diseases [7,8,9,10,11]. A method to quantify AF by standardizing measurements to an internal control has been developed [15]; it is not an absolute measure of lipofuscin because of light losses in the ocular tissues
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