Individual Retinal Pigment Epithelium Cells can be Imaged In Vivo in Age Related Macular Degeneration

Abstract

Purpose: Many retinal diseases involve the retinal pigment epithelium (RPE), but current clinical tools lack the resolution to examine the RPE mosaic at the cellular level. While our group previously showed that it is possible to image individual RPE cells in the normal eye, applying these methods to patients with retinal disease proved difficult. We have developed new methods to improve RPE imaging for practical use in patients with retinal disease, deploying them here to investigate the RPE cell mosaic in patients with age related macular degeneration (AMD).

Methods: Adaptive optics scanning light ophthalmoscopy (AOSLO) was used to image photoreceptor and RPE cells simultaneously in patients with AMD. Near-infrared light (796 nm) was used to image photoreceptors; intrinsic autofluorescence (AF) of lipofuscin was exploited to image RPE cells. AF was excited with 532 nm light at levels 22-25 times lower than the ANSI maximum permissible exposure. AF emission was collected over a 150 nm bandwidth centered at 650 nm. Excitation source and confocal pinhole were positioned initially to correct for the longitudinal chromatic aberration (LCA) of the human eye. Focus was then further refined at each location for each patient by using the deformable mirror to step through several dioptric foci to determine the focus with maximum fluorescence. After focus optimization, the confocal aperture, under computer control, was placed algorithmically to the position of greatest intensity.

Results: Individual RPE cells were resolved in two AMD patients. Abnormal RPE cell topography was observed at areas that appeared unaffected clinically. Areas larger than single RPE cells (from two to tens of RPE cells in diameter) were observed that were devoid of lipofuscin fluorescence; photoreceptor reflectance in these areas was atypical.

Conclusions: RPE images in AMD patients were obtained through new methods that allowed us to compensate for LCA. Additional improvements, such as algorithmic focus control and compensation for eye movements will further improve the efficiency of imaging RPE cells in disease. Imaging of the RPE cell mosaic with AOSLO can now be used to answer questions about diseases affecting the RPE, such as AMD, and to evaluate treatments aimed at restoring RPE health.

Keywords: 412 age-related macular degeneration • 550 imaging/image analysis: clinical • 701 retinal pigment epithelium