Comparison of Drusen Area Detected by Spectral Domain OCT and Color Fundus Photography

Abstract

Purpose: : To compare the area of drusen manually outlined on color fundus photography with the area identified using an automated algorithm designed to detect elevations of the retinal pigmented epithelium (RPE) using spectral domain optical coherence tomography (SDOCT).

Methods: : Forty-seven eyes with drusen secondary to non-exudative age-related macular degeneration (AMD) were enrolled. All eyes were imaged with the Cirrus SDOCT instrument (Carl Zeiss Meditec, Dublin, CA) using a 200x200 A-scan raster pattern centered on the fovea. This scan area measured 6mm X 6mm. Quantitative measurements of drusen were obtained by using a fully automated algorithm developed by the authors. Digital color fundus photographs were taken on the same day. The color fundus photos were registered to the OCT dataset using the OCT fundus image (OFI). Circles with diameters of 3 mm and 5 mm were positioned on both images and centered on the fovea. Drusen were traced manually on the fundus photos by experienced graders at the Doheny Image Reading Center (DIRC). Measurements inside the corresponding 3mm and 5mm circles were compared.

Results: : The mean areas (± standard deviation [range]) for the 3mm circles were SDOCT= 1.57 (±1.05 [0.03-4.12]); 3mm color fundus= 1.83 (±1.09 [0.20-3.95]); 5mm SD-OCT=2.17 (±1.55 [0.03-5.34]); 5mm color fundus=3.25 (1.87 [0.39-7.49]). The mean differences between the SDOCT and color images (SDOCT-Color) were -0.3 (±1.0) (p=0.095) for the 3mm circle and -1.1 (±1.5) (p<0.001) for the 5mm circle measurements, respectively. Intraclass correlation coefficients for 3mm and 5mm measurements were 0.519 and 0.516, respectively.

Conclusions: : There was only fair agreement between area measurements made with SDOCT and color fundus photos. The SDOCT algorithm only measured drusen that corresponded to clear deformations of the RPE geometry. Drusen areas obtained from color fundus images were larger because hypo-pigmented areas that were flat and small drusen below the sensitivity of the SDOCT instrument may not have been detected . These two approaches offer complimentary information, with SDOCT offering the ability to automatically and reliably access drusen area and volume for a subset of drusen that are elevated compared with the normal RPE contour. This drusen subset may be useful as a clinical trial endpoint when assessing therapies for the treatment of non-exudative AMD.

Keywords: age-related macular degeneration • drusen • imaging/image analysis: clinical