Quantitative Comparison of Fundus Images by 2 Ultra-Widefield Fundus Cameras

Abstract

Purpose: To compare the relative number of retinal pixels and retinal area imaged using the Optos P200DTx (Optos PLC) and Zeiss Clarus 500 (Carl Zeiss Meditec AG) ultra-widefield (UWF) fundus cameras.

Design: Single-center retrospective cross-sectional analysis.

Participants: Seventy-eight eyes of 46 patients.

Methods: Eyes were imaged with Optos P200DTx, single-capture, and Zeiss Clarus 500, 2 capture montages when possible, UWF fundus cameras. Relative number of pixels encompassing all foveal-centered retinal quadrants were measured. Retinal area was measured with Zeiss Clarus 500 images that were registered to the Optos P200DTx images. Patients and technicians were asked for preferences between the machines. Imaging session times were recorded.

Main outcome measures: Relative number of retinal pixels and retina area captured by each fundus camera.

Results: Optos P200DTx consistently captured more relative pixels compared with Zeiss Clarus 500: 510.4 versus 355.6 (P < 0.001) in total with a similarly statistically significant trend in all 4 quadrants (P < 0.001 for each). For area calculation, 70 of the 78 images achieved successful registration. Optos captured a larger total retinal area: 765.6 versus 566.5 mm² (P < 0.001) with a similarly statistically significant trend in all 4 quadrants. In the subset of 52 of 70 registered and montaged Zeiss Clarus 500 images, similar results were found. For peripheral pathologic features, Optos P200DTx captured unique findings in 28 images, and Zeiss Clarus 500 captured unique findings 1 image (P < 0.001). Among the 48 imaging sessions in which technicians preferred Optos P200DTx for 28 sessions (58%) and Zeiss Clarus 500 for 20 (42%; P = 0.15). Among patients who responded with a preference, 24 preferred Optos P200DTx and 20 preferred Zeiss Clarus 500 (P = 0.52). Average imaging session time was 4.6 minutes (standard deviation, 3.0 minutes) for Optos P200DTx and 5.2 minutes (standard deviation, 3.0 minutes) for Zeiss Clarus 500 (P = 0.17).

Conclusions: In the current study, the Optos P200DTx captured statistically significantly more retinal area in all 4 quadrants compared with the Zeiss Clarus 500. No statistically significant difference was found in patient or technician preference or image acquisition time between devices.

Keywords: Clarus; Fundus photography; Optos; Ultra-widefield; Zeiss.

Figure 1.

Fovea-centered quadrants of ultra-widefield retinal images captured by the Zeiss Clarus 500 (Carl Zeiss Meditec AG, Jena, Germany) (A) and Optos P200DTx (Optos PLC, Dunfermline, United Kingdom) (B). The dotted lines demarcate the pixels used in the calculation of relative pixel areas.

Figure 2.

Zeiss Clarus 500 (Carl Zeiss Meditec AG, Jena, Germany) (A, C) and Optos P200DTx (Optos PLC, Dunfermline, United Kingdom) (B, D) retinal images after image registration to correct for differences in image resolution and peripheral distortion with fovea-centered quadrant masks to indicate regions of interest in white for area calculation.

Figure 3.

Single-capture Zeiss Clarus 500 (Carl Zeiss Meditec AG, Jena, Germany) (A) versus single-capture Optos P200Dtx (Optos PLC, Dunfermline, United Kingdom) (B) images.