Progression of geographic atrophy in Age related Macular degeneration: Comparative analysis of methods of measurement

Abstract

Purpose : There are few methods used to measure growth of geographic atrophy (GA) in age related macular degeneration (AMD). We compared the available methods used to measure GA enlargement rate to ascertain the interchangeability of these methods

Methods : Fifty eyes of 31 patients with untreated GA secondary to AMD were randomly selected from the Moorfields Eye Hospital electronic database. To be included, gradable blue-light fundus autofluorescence (FAF) had to be available at baseline and final visit with a minimum interval of 12 mnths and lesion needed to be entirely contained in the image. Rate of GA enlargement was measured by 4 methods: subtraction of GA area change from baseline per year, square root transformation method, geographic atrophy circularity index (GACI) and distance measurement using Euclidean distance mapping. Measurements were done on FAF images. Square root transformation was considered “reference” method as it eliminates the dependency on baseline area. Main outcome measure was correlation among methods and growth rate of GA. Values expressed as the mean ± standard deviation. Bivariate correlations analysed with Spearman correlation coefficient. P value 0.05 was considered statistically significant. Analysis was performed using SPSS

Results : Mean baseline area was 3.48 ± 3.4 mm² (SEM 0.48),mean duration of follow-up 3.53 ± 2.45 years. Foveal centre was involved 54% eyes; multifocal configuration was seen in 36% eyes. Mean distance from fovea was 261.66 ± 363.86 μm. Mean rate of growth per year was 0.33 ± 0.18 mm/year with square root transformation, 1.5 ± 1 mm²/ year with area measurement, 66 ± 43µm/ year by distance mapping and mean GACI index was 0.57 ± 0.23. On a continuous scale of GACI, there was significant correlation between subtraction method growth rate and GACI both for measurements in mm² (r -0.53, P <0.001) and for square root transformed measurements (r -0.52, P < 0.001). However there was poor correlation between square root transformation method and distance mapping (r 0.04, P = 0.73). There was a negative correlation between GACI and distance mapping but it was not statistically significant (r -0.06, P = 0.65)

Conclusions : Linear distance based measurement did not correlate with area based measures of GA progression. This may be of relevance to future quantitative studies evaluating growth progression in lesions with centrifugal growth like GA

This is a 2020 ARVO Annual Meeting abstract.