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T. R. Burke, S. H. Tsang, J. P. Greenberg, T. Duncker, J. R. Sparrow, G. R. Barile, F. C. Delori, T. Smith; Absolute Autofluorescence (AbsAF) in Stargardt Disease (STGD). Invest. Ophthalmol. Vis. Sci. 2010;51(13):4054.
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To demonstrate AbsAF levels in patients with STGD can correlate with in vivo lipofuscin levels.
AbsAF measurements were done on 22 patients with STGD (ages 10 to 67 yrs, 37 eyes) using the HRA2 (Heidelberg Engineering Inc., Vista, CA) modified by insertion of a fluorescence reference chip in a retinal image plane (Fig 1). Correction was made for refractive error and optical media density from normative data.
Median AbsAF values in the central 3000 micron diameter region as well as superior and temporal macular regions were compared to the data from age matched controls.The internal fluorescence reference (horizontal strip) is at the top of each image. The AbsAF images are generated by Matlab using the formula in Fig 2 - SC is the refractive error correction and (T-1om,488T-1om,emi) is the optical media density correction. The zero (GL0) is calculated from darkest pixels, usually at the optic disc. The reference gray level (GLR) is measured from the original AF images. Two tailed t-test was used for analysis.Results: Excluding 10 eyes of 6 patients where atrophy or poor centration precluded imaging of focal macular hyperfluorescence, background levels of AbsAF were found to be significantly elevated relative to controls (Table 1, Chart 1) and levels 400% greater were detected in flecks compared with background AbsAF in STGD patients (mean fleck: 159.7, mean background: 94.5, p<0.003), while areas in the transition zone from hyper to hypofluorescence (atrophy) demonstrate levels double the highest background levels in STGD.
Absolute AF measurements in STGD can shed quantitative light on the disease process which is not possible with previous in vivo imaging techniques. This will not only help with monitoring disease progression, but will be a useful marker of individual mutation effect and of response to interventional therapies in the future. Our patients demonstrate a markedly increased level of AbsAF in youth, but tapering with age as atrophy of the pigment epithelium ensues. Flecks and transition zones show the highest AbsAF.
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