Riggs-type dominant congenital stationary night blindness: ERG findings,a new <Emphasis Type="Italic">GNAT1</Emphasis> mutation and a systemic association

Purpose

To characterize the ultrastructural and functional correlates of hydroxychloroquine (HCQ)-induced subclinical bull’s eye lesion seen on near-infrared reflectance (NIR) imaging.

Methods

An asymptomatic 54-year-old male taking HCQ presented with paracentral ring-like scotoma, abnormal multifocal electroretinography (mfERG) and preserved ellipsoid zone on optical coherence tomography (OCT). Dense raster OCT was performed to create en face reflectivity maps of the interdigitation zone. Macular Integrity Assessment (MAIA) microperimetry and mfERG findings were compared with NIR imaging, en face OCT, retinal thickness profiles and wave-guiding cone density maps derived from flood-illumination adaptive optics (AO) retinal photography.

Results

The bull’s eye lesion is an oval annular zone of increased reflectivity on NIR with an outer diameter of 1450 µm. This region corresponds exactly to an area of preserved interdigitation zone reflectivity in en face OCT images and of normal cone density on AO imaging. Immediately surrounding the bull’s eye lesion is an annular zone (3°–12° eccentricity) of depressed retinal sensitivity on MAIA and reduced amplitude density on mfERG. Wave-guiding cone density at 2° temporal was 25,400 per mm². This declined rapidly to 12,900 and 1200 per mm² at 3° and 4°.

Conclusion

Multimodal imaging illustrated pathology in the area surrounding the NIR bull’s eye, characterized by reduced reflectance, wave-guiding cone density and retinal function. Further studies are required to investigate whether the bull’s eye on NIR imaging and en face OCT is prominent or consistent enough for diagnostic use.