Functional correlates of fundus autofluorescence abnormalities in patients with RPGR or RIMS1 mutations causing cone or cone rod dystrophy

Aim:

The aim of this study was to establish the functional significance of annular macular abnormalities present on fundus autofluorescence imaging (AF) in patients with cone or cone–rod dystrophy.

Methods:

Fundus AF was performed on ten subjects (age range 18–82 years) with cone or cone–rod dystrophy consequent upon RPGR or RIMS1 mutation. International-standard full-field and pattern electroretinograms (ERGs) were performed in all cases. Photopic and scotopic fine matrix mapping (FMM) and multifocal ERG were performed on selected cases.

Results:

Subjects had annuli of high density AF that bordered central areas of low density in older RPGR cases and most RIMS1 cases. The size of the AF ring correlated with age and enlarged with time in two subjects. High-density rings were associated with a gradient of scotopic and photopic sensitivity loss. Pattern electroretinogram (PERG) P50 amplitude, when detectable, was inversely related to the size of the AF ring. Multifocal ERGs in two subjects showed widespread reduction with relative sparing over the foveal area, in keeping with FMM data.

Conclusions:

Some patients with cone–rod dystrophy have a parafoveal ring of increased autofluorescence that may enlarge with time. Increased autofluorescence is associated with reduced rod and cone sensitivity, rather than photoreceptor cell death, and AF imaging may help identify viable areas of retina amenable to future therapeutic intervention.