Differential Retro mode imaging for improved drusen visualization: a preliminary study

Purpose. Off-axis retroillumination (known as "Retro mode”) has been shown to enhance the detection of drusen, particularly smaller lesions. Images are obtained by shifting the aperture left (DL) or right (DR), each revealing complementary aspects of drusen. This study evaluated whether combining DL and DR images could improve drusen assessment. Methods. Multimodal images from 11 patients (mean age 74.5 ± 12.1 years; 8 females) with early or intermediate age-related macular degeneration (AMD) were retrospectively analyzed. Imaging included pseudocolor photographs, Retro mode (Mirante, NIDEK), and optical coherence tomography (OCT; Cirrus 5000, Zeiss). DL and DR Retro mode images were manually aligned using vascular landmarks, and differential images (DIF) were generated with FIJI (ImageJ). Results. DIF images improved lesion delineation compared with individual DL or DR images. Hard drusen were barely visible on pseudocolor photographs and en face OCT but were clearly identified with Retro mode; on DIF images, they appeared larger than on DL or DR images. Intermediate drusen were visible across all modalities, and Bland–Altman analysis showed slightly larger areas on DIF compared with en face OCT (mean difference: +2.2%). Soft drusen also appeared larger on DIF, with an average overestimation of 14.5% compared with pseudocolor. DIF images further supported the characterization of cuticular drusen and pseudodrusen (SDD). Conclusion. This preliminary study indicates that Retro mode imaging of drusen can be refined through alignment and differential analysis of DL and DR images, providing more complete surface visualization and potentially improving the characterization of AMD stages.