Progression, reliability, predicting parameters and sample size calculations for quantitative fundus autofluorescence measures inABCA4-related retinopathy

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Background/aims To investigate the progression of quantitative autofluorescence (qAF) measures and the potential as clinical trial endpoint inABCA4-related retinopathy. Methods In this longitudinal monocentre study, 64 patients withABCA4-related retinopathy (age (mean±SD), 34.84±16.36 years) underwent serial retinal imaging, including optical coherence tomography (OCT) and qAF (488 nm excitation) imaging using a modified confocal scanning laser ophthalmoscope with a mean (±SD) review period of 20.32±10.90 months. A group of 110 healthy subjects served as controls. Retest variability, changes of qAF measures over time and its association with genotype and phenotype were analysed. Furthermore, individual prognostic feature importance was assessed, and sample size calculations for future interventional trials were performed. Results Compared with controls, qAF levels of patients were significantly elevated. The test–retest reliability revealed a 95% coefficient of repeatability of 20.37. During the observation time, young patients, patients with a mild phenotype (morphological and functional) and patients with mild mutations showed an absolute and relative increase in qAF values, while patients with advanced disease manifestation (morphological and functional), and homozygous mutations at adulthood revealed a decrease in qAF. Considering these parameters, required sample size and study duration could significantly be reduced. Conclusion Under standardised settings with elaborated conditions towards operators and analysis to counterbalance variability, qAF imaging might be reliable, suitable for quantifying disease progression and constitutes a potential clinical surrogate marker inABCA4-related retinopathy. Trial design based on patients’ baseline characteristics and genotype has the potential to provide benefits regarding required cohort size and absolute number of visits.

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