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Janet R Sparrow, Maarjaliis Paavo, Hye Jin Kim, Jin Zhao, Winston Lee, Rando Allikmets, Stephen H Tsang; Measuring Short Wavelength and Near Infrared Fundus Autofluorescence in the presence of ABCA4 Mutations and Albinism. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5856.
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© ARVO (1962-2015); The Authors (2016-present)
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.
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.
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.
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.
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