Quantitative Phenotyping of Stargardt Disease: A Comparison Between Novel Psychophysical Perimetric Techniques and Multifocal Electrophysiology

Abstract

Abstract: : Purpose: The purpose of the present investigation is to identify and describe any correlation between the psychophysical phenotype and multifocal electroretinograms in 7 families with Stargardt disease (SD). Methods: To quantify the psychophysical phenotype of all subjects (n= 10 patients and 6 normal relatives, identified in our University Clinic, and age–matched normal controls, n=25) we have evaluated chromatic performance with an anomaloscope (IF–2) and a modified version of the Cambridge Colour Test to obtain protan, deutan, tritan and discrimination ellipses’ measures. Subjects also underwent a perimetric testing custom–based procedure under photopic conditions. We obtained contrast threshold measures in 17 locations with random staircases using two different conditions. The first isolated the magnocelular pathway (frequency–doubling technique) and the second stimuli had a stronger parvocelular bias. Multifocal ERGs were also obtained according to current standards. Results: Chromatic performance was profoundly impaired along all cone confusion axes. Magnocellular perimetry revealed significant impairment in SD patients in comparison both to their relatives and controls (p = 0.016 and p < 0.0001). Parvo–biased perimetry showed similar results (p < 0.0001, both comparisons). Interestingly, performance was significantly impaired across the whole visual field (central 5º; Zone 1, 5–10º eccentricity; and Zone 2, 10–20º) for both types of perimetric assessment. Multifocal ERGs revealed reduced amplitudes of a and b waves not exclusive to the macular region. Latency measures show small but significant differences between SD subjects and controls. A very interesting performance pattern was observed in SD normal relatives: they were significantly better than SD subjects in all measures. Furthermore magnocellular perimetry and mERG latencies showed results comparable to normals. However parvo–biased perimetry and mERG amplitudes were significantly worse than in controls. Conclusions: Magno and parvocellular functions are impaired in SD, both in parafoveal and more peripheral visual field locations. These findings parallel amplitudes and latency changes found in mERG. Quantitative contrast sensitivity perimetry seems to be a promising phenotyping strategy in SD.

Keywords: macula/fovea • electroretinography: clinical • degenerations/dystrophies