Session Title: Imaging I
Session Date/Time: Friday 12/09/2014 | 11:00-13:00
Paper Time: 11:56
Venue: Boulevard D
First Author: : T.Burke USA
Co Author(s): : T. Duncker R.L. Woods R.T. Smith R. Allikmets J.R. Sparrow F. Delori
To quantify fundus autofluorescence (qAF) in patients with autosomal recessive Stargardt disease (STGD1).
Edward S. Harkness Eye Institute, Columbia University, New York, New York.
42 STGD1 patients (ages: 7-52 years) with at least one confirmed disease-associated ABCA4 mutation were studied. Fundus AF images (488 nm excitation) were acquired with a confocal scanning laser ophthalmoscope equipped with an internal fluorescent reference to account for variable laser power and detector sensitivity. The gray levels (GLs) of each image were calibrated to the reference, zero GL, magnification, and normative optical media density to yield qAF. Patients were assigned to one of three the phenotype groups as described by Fishman: Fishman I, pigmentary changes and/or atrophy in the fovea and no flecks outside a disc diameter circle centered on the fovea; Fishman II, flecks throughout the posterior pole, which often extended anterior to the vascular arcades and/or nasal to the optic disc; and Fishman III, ‘resorbed’ flecks with widespread atrophy of the RPE.
qAF in 35/42 patients (54/64 eyes) was above normal limits for age. Young patients exhibited the relatively highest qAF, with levels up to 8-fold higher than healthy eyes. In Fishman II, qAF was higher than in Fishman I patients, but qAF values of Fishman III were not significantly different from those of Fishman I and II patients. qAF was within the normal range for 9 of 34 Fishman I eyes, while few Fishman II (1/20) and no Fishman III (0/10) eyes had a qAF within the normal range. Patients carrying the most common ABCA4 mutation, G1916E, had lower qAF than most other patients, even in the presence of a second allele associated with severe disease. In 25 eyes (19 patients, all Fishman I) the AF image appeared clinically normal in the sampled regions with no obvious high AF flecks nor other AF abnormalities. Even so, the qAF levels in these eyes were significantly elevated compared to the healthy eyes. Repeatability of qAF measurements was not significantly different from that observed in healthy subjects. Furthermore, of the 22 subjects with bilateral qAF data available, the values for the right and left eyes were found to be highly correlated.
qAF is an indirect approach to measuring RPE lipofuscin in vivo. We report that ABCA4 mutations cause significantly elevated qAF, consistent with previous reports indicating that increased RPE lipofuscin is a hallmark of STGD1. Even when qualitative differences in fundus AF images are not evident, qAF can elucidate phenotypic variation. qAF will serve to establish genotype-phenotype correlations and as an outcome measure in clinical trials by allowing reproducible quantification of AF levels in individual patients, inter-patient comparison and monitoring of AF levels longitudinally. It would also permit the comparison of data acquired on different devices at several centers.