Analysis of autofluorescent retinal images and measurement of atrophic lesion growth in Stargardt disease

Current retinal imaging techniques using scanning laser ophthalmoscopy (SLO) provide a powerful mechanism for characterizing the topographical distribution of lipofuscin fluorophores and atrophic lesions (ALs) in retinal disease. In this paper we describe a novel Edge-Flow-Driven Variational Image Segmentation analysis to measure and evaluate progressive change in the area of ALs as well as regions of hyperfluorescence (HF). The algorithm is embedded in a series of almost completely automated image processing steps that allow rapid comparison of serial images. The sensitivity of the methodology to detect change was evaluated by measuring progression of AF lesion size in a cohort of Stargardt Macular Dystrophy (STGD) patients. Fifty-two STGD subjects (mean age = 41.0 +/- 16.6 years, range 9-78 yrs) at varying stages of disease participated in this prospective study. Twenty-four of the 52 subjects presented with atrophic lesions in one or both eyes on first evaluation. For this subgroup of subjects, the mean (+/-1 sd) follow-up time was 2.92 (+0.26) years (range 0.57-3.26 years) and the mean (+/-1 sd) rate of change was found to be approximately 0.94 (+/-0.87) mm(2)/year (range 0.2-2.13 mm(2)/yr). With this methodology, progressive enlargement of AL area was detectable in as little as one year, while regions of HF generally decreased, although there was considerable variability in the appearnce of HF, presumably reflecting the combined effects of the creation or expansion of lipofuscin deposits and resorption and loss associated with retinal cell death. Our findings suggest that this methodology is sufficiently sensitive to detect change and provides a clinically relevant tool to monitor progression not only with regards to natural history, but also to evaluate the efficacy of potential therapeutic interventions in STGD. Finally, we evaluated the association between AL area and measures of rod- and cone-mediated retinal function, as assessed with electroretinography (ERG). In general, the larger the AL, the poorer the ERG response, with a greater impact of lesion size on cone- rather than rod-mediated retinal function, a finding that was expected on the basis of the location and size of the AL and the distribution of rod- and cone-photoreceptors.