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C. N. Keilhauer-Strachwitz, F. C. Delori; Rate of Progression of Geographic Atrophy. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4926.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the progression rate of geographic atrophy (GA) in AMD, and study its dependence upon age and eccentricity.
Progression of GA in 31 patients (ages: 58-87 years) was studied using autofluorescence images (HRAc, Heidelberg Eng. Heidelberg, Germany) obtained during 2 to 5 follow-up visits. The median interval between visits was 1.1 year (range: 0.5 - 4.8 years). Images from each patient were aligned with each other. The contour of each GA was determined using an image analysis method that defines the junction as the half grey-level point at 75 - 200 points along the perimeter. The area of the GA was computed by integration. We characterized GA progression between visits by a linear progression rate (LPR), defined as the mean distance between the 2 contours (perpendicular to the 1st contour) divided by the time interval (µm/year). We excluded segments of the contours where the first GA was increased by small visible zones of atrophy to form the subsequent contour.
Mean area of the GA’s was 4.6±4.3 mm² at the 1st visit (0.6-15 mm²). The area of all GA’s suggested a parabolic-like increase with age. For all contours pairs, the mean LPR was 141±71 µm/year (mean area progression rate : 1.2±0.9 mm²/year). For 24 patients that had 3 or more visits, the LPR was 137±69 µm/year for the 1st time interval, significantly higher than 108±45 µm/year for the 2nd interval (p=0.001). The LPR for both intervals correlated with each other (p=0.0008). A decrease in LPR also occurred between the 2nd and 3rd interval for 8 patients with 4 visits or more (p=0.02). The decrease in LPR with time was less pronounced at older ages (p=0.03, n=24). Mean LPR for small areas of atrophy (area < 0.4 mm², n=10) located outside the main GA in 6 patients was 34±24 µm/year, substantially smaller than the LPR of the main GA (128±46 µm/year) during the same interval (p=0.0001).
In the range of GA areas studied, the speed at which the edge of a GA progresses decreased with time. A constant LPR or a continuously decreasing LPR (to a constant level) are both consistent with a parabolic-like increase of the GA area with age. Although the slow progression rate of peripheral zones of atrophy may appear contradictory, estimates of LPR from the central area in early stages of the progression are needed to better understand this observation. Information on how GA enlarges is of interest for a better understanding of the events associated with retinal degeneration as well as for sensitively monitoring the effect of treatment.
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