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Grace Huang, Sumana S Kommana, Bernard C Szirth, Albert S Khouri; Reliability of a Novel Quantitative Standardized Measurement Technique for Fundus Autofluorescence Imaging. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):590.
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© ARVO (1962-2015); The Authors (2016-present)
FAF images are currently analyzed descriptively and qualitatively. The purpose is to assess the reliability of a new standardized measurement technique designed to quantitatively analyze fundus autofluorescence (FAF) images.
FAF photos were captured in eyes of healthy subjects using a Canon CX-1 Hybrid Mydriatic/Non-mydriatic retinal camera. Single static images were captured using a flash power of 300 w/sec with a wide band excitation and barrier filter (535-585 nm and 605-715 nm, respectively) and a 45 degree field of view (FOV). The zone between the temporal edge of the optic nerve (ON) and macula (M), designated as the papillo-macular zone (P), of each image was chosen and analyzed by assigning a grayscale pixel intensity, ranging from 0 (black) to 256 (white). A grayscale pixel score was determined for each image (Figure 1). To reduce background noise, the same images were then “standardized” using a technique, which adjusted a square area (1.80 x 1.80mm) overlying the ON to an intensity of 0 (Figure 2). In order to determine the consistency of the scoring, the standardized images were analyzed twice, blindly on two separate occasions by one observer. Means, standard deviations (SD), t-tests, and an intra-class correlation (ICC) were performed.
In total, 96 images were analyzed (from the left eye of 32 subjects, mean age=23 yrs). Two eyes had poor quality FAF images and were excluded from the analysis. In the non-standardized image readings, the mean pixel intensity for zone P was 84.64±29.27. After standardization to reduce background noise, the mean pixel intensity for zone P was highly comparable between the two readings: 38.80±12.81 on the first read (R1) and 38.78 ± 12.84 on the second read (R2) (p=0.99). The intra-class correlation between the two standardized readings was 0.99.
This novel standardized technique applied to FAF images was strongly reliable and reproducible and can yield scores that quantify autofluorescence in a preselected zone in the fundus. Clinical applications will allow quantitative scoring of FAF and follow-up in clinical therapeutic and research settings. A larger study testing this quantitative scoring system in different demographic populations are needed to further characterize the full utility of this modality.
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