Abstract
Purpose :
We studied NIR-AF and SW-AF images acquired from patients carrying mutations in ABCA4; carriers of GPR143/OA1 mutations conferring ocular albinism; and mice differing in their content of RPE melanin and lipofuscin.
Methods :
Short wavelength (488 nm, SW-AF) and near-infrared (787 nm, NIR-AF) fundus autofluorescence images were acquired from STGD1 patients, GPR143/OA1 carriers, albino and agouti Abca4-/- mice, wild-type mice and agouti Rdh8-/-Abca4-/- mice. SW-AF intensity was measured by quantitative fundus autofluorescence (qAF) and NIR-AF was measured as grey levels in non-normalized images acquired with a fixed sensitivity.
Results :
The fundus of GPR143/OA1 carriers presented with pigmentary mosaicism. At an eccentricity of 7-9°, qAF was within levels observed in age-matched healthy eyes. Color coded qAF maps and NIR-AF images revealed that the pigmented areas of the mosaic having NIR-AF signal also exhibited qAF levels commiserate with age-matched healthy eyes whereas the hypopigmented areas had significantly higher focal areas of SW-AF. In patients having ABCA4-associated disease, NIR-AF intensities were elevated in tandem with increased qAF. The NIR-AF signal in agouti Abca4-/- mice, having elevated qAF relative to wild-type was greater than in agouti Abca4+/+ mice on the same genetic background. qAF and the NIR-AF signal were also higher in the albino Abca4-/- mice as compared to wild-type. Black C57BL/6J mice and albino C57BL/6Jc2j mice presented with similar qAF even though by chromatographic quantitation, bisretinoids were present in lesser amounts in albino eyes due to loss by photooxidation and photodegradation.
Conclusions :
RPE melanin attenuates the SW-AF signal. Conversely, the more intense SW-AF recorded in melanin-free fundus areas of GPR143/OA1 carriers and albino mice is attributable to greater irradiance received by the RPE cell fluorophores. While NIR-AF was greatly reduced in the patches of melanin-deficient fundus, en face IR reflectance did not present as a mosaic in the fundus of OA1 carriers. The mosaicism of the fundus in NIR-AF images was consistent with the NIR-AF signal originating primarily from melanin. However, the increase in NIR-AF intensity that paralleled increases in SW-AF due to ABCA4 deficiency in patients and mice indicates that RPE bisretinoid lipofuscin makes a contribution to NIR-AF.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.