Short-wavelength and near-Infrared fundus autofluorescence in blue light-illuminated Abca4^-/- mice and a patient with Stargardt disease

Abstract

Purpose : Fundus autofluorescence imaging is a noninvasive technique for diagnosing retinopathies, such as Stargardt disease (SD). The interpretation of short- wavelength (SW) fundus autofluorescence (AF) and near-infrared (NIR) AF alterations of retina disease is not fully studied.To determine histological features of aberrances in SW-AF and NIR-AF, we investigated blue light-illuminated Abca4^-/- mice and perimacular tissue from a donor with Stargardt disease.

Methods : Pigmented Abca4^−/− mice (129S4/SvJae-Abca4^tm1Ght) were illuminated with blue light (430nm, 50mW/cm², 15 min). Fundus AF in modalities of SW-AF and NIR-AF and spectral-domain optical coherence tomography (SD-OCT) were recorded 7 days after blue light illumination. Semithin sections were observed under light microscope and fluorescence microscope (filter for lipofuscin: excitation 360 nm, emission 540 nm; filter for NIR fluorescence: excitation 750 nm, emission 773nm). Ultrastructure was analyzed by electron microscope. Fundus AF images were correlated to histological analysis. Semithin sections of a 72-year-old donor with Stargardt disease were examined under fluorescence microscope with both filters.

Results : In blue light-illuminated Abca4^−/− mice, patches with fundus hyper AF in both modalities of SW-AF and NIR-AF correlated with hyperreflective bands in OCT and appeared as accumulation of high number of macrophages in the subretinal space. Macrophages were observed with hyperAF under fluorescence microscope with both filters. Lesion areas of complete loss of RPE and photoreceptors were observed with loss of AF. In the human donor eye with late Stargardt disease, hyperAF of lipofuscin was observed in RPE cells. The prominent cluster with lipofuscin AF in RPE layer as shown earlier (Taubitz et al (2018). PeerJ 6: e5215) exhibited extremely hyper NIR-AF under fluorescence microscope. Photoreceptors were not observed with lipofuscin-AF or NIR-AF.

Conclusions : Accumulation of macrophages which phagocytose the debris containing high concentrations of melanosomes, melanolipofuscin and lipofuscin granules results in fundus hyperAF in modalities of SW-AF and NIR-AF in blue light-illuminated pigmented Abca4^-/- mice. Blue light induced geographic atrophy results in loss of AF. In eye with Stargardt disease, the pigment cluster expresses high NIR-AF inidicating changes in the chemical compositions of melanin.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.