Autofluorescence changes in the AMD retina

Abstract

 

Purpose

 

While etiological research of age-related macular degeneration (AMD) has blossomed and produced numerous theories and cellular observations, there is a gap to the clinical application of this new knowledge as well as an opportunity for its use in the early detection of AMD. We investigated the autofluorescence (AF) changes of microscopic and macroscopic features of the AMD retina, using techniques with clinical utility, in order to evaluate their potential as disease markers.

 

Methods

 

Globes of 4 donors with AMD (mean age 73) and 4 controls (mean age 72.75) were embedded in paraffin and sectioned through the macula. Sections were excited using a 488nm laser, and the AF emission spectra were captured with a confocal microscope. Individual lipofuscin and melanolipofuscin granules were manually identified in each section and analyzed, along with portions of Bruch’s membrane and drusen (Figure 1). The peak emission wavelengths of the AMD and control groups were compared in each case (Table 1). Further analysis will be performed on larger areas of retina.

 

Results

 

In all comparisons, the AMD eyes had a consistently blue-shifted emission peak compared with control. These changes were not statistically significant at the microscopic level (i.e. RPE granules or Bruch’s membrane) in either the periphery or macula. However, the consistency of these spectra will be used to automate the selection of larger areas of retina. This will allow for analysis of macroscopic areas that contain multiple elements, yielding a more complete comparison of retina.

 

Conclusions

 

While not statistically significant at a microscopic level, our results indicate that there may exist a spectral change in the AMD retina compared with control. While our imaging approach involved a bench top system with ex-vivo tissue specimens in an ideal configuration to minimize background and scatter, it is conceivable that similar spectral changes could be detected using 488nm AF imaging in vivo as an early marker for AMD. Our next step will be to compare larger areas of retina in AMD and control tissue.  

 

Figure 1 - AF emission in AMD retina of drusen, Bruch's membrane, lipofuscin (LP), and melanolipofuscin (MLP) granules selected for spectral analysis and comparison.

 

 

Table 1 - Peak wavelengths of retina regions of interest as determined by polynomial fit. Mean peak wavelengths of AMD and control populations (n=4 for each) were compared using a two-tailed t-test.