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M. A. Sohrab, S. Tsang, J. Greenberg, T. Duncker, J. Sparrow, F. Delori, R. Smith; Absolute Autofluorescence (AbsAF) Measurements in Retinitis Pigmentosa (RP). Invest. Ophthalmol. Vis. Sci. 2010;51(13):1369.
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Absolute Autofluorescence (AbsAF) measurement of in vivo lipofuscin levels in RP patients.
AbsAF measurement (in AbsAF units) was done on 6 patients with RP (ages 17-62, 6 eyes) with clear crystalline lenses using HRA2 (Heidelberg Engineering Inc., Vista, CA) modified by insertion of a fluorescence reference chip in the retinal image plane (Fig. 1). Correction was made for the internal standard, optical media density from normative data, and refractive error. Reproducibility and normative data for age had been verified on a large set of normal subjects. Only patients with a hyperfluorescent ring were included. Median AbsAF values in the central 3000 micron region and median AbsAF value of the brightest 1000 micron region on the ring were measured and compared to the corresponding regions of an aged-matched normal retina. Other data included MP1 and SD-OCT.
AbsAF measurements of the hyperfluorescent rings were significantly higher than for corresponding age-matched normals (Fig. 2).Figure 1. Examples of AbsAF measurement in RP patients (ages 14 & 42 yrs). The internal fluorescence reference is seen at the top of each image. The reference gray level (GLR) is measured in the original images (top). GL0 is calculated from darkest pixels on the optic disc. The AbsAF images, color coded below, are generated by: AbsAF = [SC (GL x T-1om,488 x T-1om,emi - GLo)]/ (GLR - GLo) SC = refractive error correction; optical media density = T-1om,488 T-1om,emiFigure 2. AbsAF units of RP patients versus normals. Scatter plot of data from 6 RP patients versus age-matched controls showing much higher AbsAF levels in RP patients.
The hyperfluoresent ring seen in some RP patients shows elevated AbsAF lipofuscin measurements. The extent of the ring seen on AbsAF can be correlated with the IS/OS junction loss seen on horizontal OCT line scans. Regular AF may underestimate the true extent of structural abnormality. AbsAF in RP and other retinal degenerative diseases can shed quantitative light on disease processes that is not possible with other in vivo techniques.
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