Bifocal retinal degeneration observed on ultra-widefield autofluorescence in some cases of CRX-associated retinopathy.

Background: Variants in CRX are associated with dominantly inherited retinopathy with considerable phenotypic variability. Many patients have central retinal degeneration; in some patients, we have observed an additional focus of degeneration in the nasal retina. This study explores this phenotypic association amongst patients with CRX-associated disease.

Methods: A retrospective review was conducted for all patients with dominant CRX-associated retinopathy at two UK centres. Analysis focused on patients with available ultra-widefield autofluorescence imaging and aimed to identify those with a specific bifocal degeneration pattern involving the nasal retina in both eyes.

Results: Sixty patients were identified, with ultra-widefield fundus imaging available for 50 patients. Of these, six male patients aged 26-74 years displayed a distinct pattern characterised by central retinal degeneration and an additional discrete area of altered autofluorescence in the nasal periphery. Pattern and full-field ERGs indicated macular dysfunction in all 6 cases, with generalised cone (n = 2) or cone and rod (n = 4) system involvement, with a locus that appeared to be post-phototransduction. The CRX variants found in these patients included missense variants (n = 2), frameshifting variants (n = 3), and a CRX whole gene deletion (n = 1), with no clear genotype-phenotype correlation identified.

Conclusions: We report a distinct pattern of bifocal retinal degeneration in some cases of CRX-associated retinopathy (12% in our cohort), not typically seen in other forms of inherited retinal disease. Recognising such phenotypes can guide genetic investigations or their interpretation, facilitating molecular diagnoses for effective family counselling, given the autosomal dominant inheritance and phenotypic variability of CRX-associated retinopathy.