Are the Hypo-Reflective Clumps Associated With Age-Related Macular Degeneration in Adaptive Optics Ophthalmoscopy Autofluorescent?

Hypo-reflective clumps (HRCs) are structures associated with age-related macular degeneration (AMD) that were identified using flood-illumination adaptive optics ophthalmoscopy (FIAO) and hypothesized to be either macrophages that have accumulated melanin through the phagocytosis of retinal pigmented epithelial (RPE) cell organelles or transdifferentiated RPE cells. HRCs may be autofluorescent (AF) in the near infrared (NIR) but clinical NIR autofluorescence imaging lacks the resolution to answer this question definitively. Here, we used near infrared autofluorescence (NIRAF) imaging in fluorescence adaptive optics scanning laser ophthalmoscopy (AOSLO) to determine whether HRCs are AF. Patients with AMD and HRCs underwent imaging with FIAO, optical coherence tomography (OCT), and multi-modal AOSLO (confocal, NIRAF, and non-confocal multi-offset detection using a fiber bundle). HRCs were segmented on FIAO and images, co-registered across modalities, and HRC morphometry and AF were quantified. Eight patients participated (mean age = 79 years, standard deviation [SD] = 5.7, range = 69-89 years, and 5 female patients). Most HRCs (86%, n = 153/178) were autofluorescent on AOSLO. HRC AF signal varied but most uniformly dark HRCs on FIAO showed corresponding AF on AOSLO, whereas heterogeneous HRCs showed a smaller AF area or no AF. These findings are consistent with the hypothesis that HRCs contain AF RPE organelles. A small proportion of HRCs were not AF; these may represent macrophages that have not yet accumulated enough organelles to become AF. HRCs may have clinical significance but further study is needed to understand the interplay among HRCs, RPE cells, and macrophages, and their relationship to geographic atrophy (GA) progression in AMD.