Progression of Geographic Atrophy Imaged With Spectral Domain OCT

Abstract

Purpose: : To characterize the appearance and progression of geographic atrophy (GA) in patients with age-related macular degeneration (AMD) using spectral domain OCT (SDOCT) fundus imaging.

Methods: : Patients with geographic atrophy secondary to AMD were enrolled in an ongoing prospective SDOCT study at the Bascom Palmer Eye Institute and imaged using the Cirrus high-definition OCT (Carl Zeiss Meditec, Dublin, CA). Routinely, eyes were imaged using the 200 A-scan by 200 B-scan raster pattern contained within a 6mm X 6mm area. The acquired three-dimensional data were then be used to create an OCT Fundus Image (OFI).For inclusion in this study, the GA lesions had to be contained within the 6mmX6mm area of the OFI centered on the fovea and followed for at least 6 months. Areas of GA were quantified from the OFI after exporting the files to a CintiQ WACOM digitizing tablet (WACOM Corp., Vancouver, WA) and the boundaries were drawn by hand.

Results: : Out of 319 patients with GA scanned using the SDOCT protocol, 40 eyes of 33 patients had GA contained within the central 6mm X 6mm area and were followed for at least 6 months. At baseline, 40 % of eyes had a single contiguous area of GA while 60% of eyes had multifocal areas of GA. The average total area at baseline was 4.9mm² (1.93 disc areas (DA) with a median area of 3.62mm² (1.42DA)) and a range of GA from 0.7 mm² to 14.587mm². The mean follow-up time was 1 year. On average, the enlargement rate (ER) per year of GA was 1.14mm² (0.44 disc areas). While there was a correlation between the baseline area of GA and enlargement rate, the enlargement rate was highly variable for any given baseline area (r=0.62, p<0.001; Spearman rho=0.58, p<0.001 ). The dependency of ER on the baseline area of GA was best shown by separating eyes into two groups; eyes with a baseline area of GA < 2DA (<5.08 mm²) and eyes with GA ≥2 DA (≥5.08 mm²). There was a significant difference in ER between the two groups (p<0.001; 2 sample t-test). Eye with GA <2DA enlarged at a rate of 0.84 mm²/yr compared with a rate of 1.77mm² for eyes with GA measuring ≥2 DA.

Conclusions: : SDOCT imaging is useful for imaging GA. When using the OFI to assess the enlargement rates of GA, we found that lesions ≥2 DAs enlarged at a much faster rate than smaller lesions. Unlike other imaging modalities commonly used to assess disease progression in dry AMD such as color fundus photography, autofluorescence, and fluorescein angiography, SDOCT imaging is unique in providing 3D morphological assessment of both drusen and GA.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • age-related macular degeneration • imaging/image analysis: clinical