Abstract
Purpose To present new clinical features, multimodal and ultrawide-field imaging characteristics of peripheral cone dystrophy (PCD), and results of laboratory and genetic investigation to decipher the etiology. Methods Retrospective observational case-series. Results Three patients with PCD presented with bilateral paracentral scotomas and a mean visual acuity of 20/25. All exhibited confluent macular hyperautofluorescence with a central bull's eye lesion. Spectral-domain optical coherence tomography revealed loss of outer retinal elements, particularly the inner segment ellipsoid band and external limiting membrane, within the area of macular hyperautofluorescence. This area corresponded with a lightened fundus appearance and variable retinal pigment epithelium (RPE) abnormalities. Full field and multifocal electroretinography distinguished PCD from other photoreceptor dystrophies. Ultrawide-field imaging revealed irregular peripheral retinal lesions in a distribution greater nasally than temporally and not contiguous with the macular lesion. Functional and anatomic testing remained stable over a mean follow-up of 3 years. Laboratory investigation for causes of uveitis was negative. Whole exome sequencing identified rare variants in genes associated with macular or cone dystrophy or degeneration. Conclusions In contrast to the original description, the funduscopic and fluorescein angiographic appearance of PCD is abnormal, although the defects are subtle. Peripheral lesions may be observed in some patients. Bilateral, symmetric, macular hyperautofluorescence associated with outer retinal atrophy that spares the fovea is a characteristic of PCD. Pathogenic variants in the same gene were not shared across the cohort, suggesting genetic heterogeneity. Further evaluation is warranted.
Highlights
Cone dystrophy is a slowly progressive, diffuse photoreceptor dystrophy that presents as hemeralopia, reduced visual acuity, and nystagmus associated with macular cone photoreceptor and retinal pigment epithelium (RPE) atrophy [1,2,3,4,5,6]
Review of the fundus photography and fluorescein angiography images from the report by Kondo and coauthors demonstrates the same features we describe in our cohort: (a) a lightened macular color funduscopically that transitions at the temporal arcades, (b) narrowing of retinal vessels within the affected macular region, (c) macular hyperfluorescence on FA that transitions at the same location as the funduscopic color change, and (d) variable blocked choroidal fluorescence outside the macular lesion
We assert that peripheral cone dystrophy (PCD) has features on ophthalmoscopy and multimodal imaging that distinguishes this diagnosis from other rare diseases
Summary
Cone dystrophy is a slowly progressive, diffuse photoreceptor dystrophy that presents as hemeralopia, reduced visual acuity, and nystagmus associated with macular cone photoreceptor and retinal pigment epithelium (RPE) atrophy [1,2,3,4,5,6]. Two forms of localized cone dysfunction syndromes have been described: occult macular dystrophy (OCMD; MIM 613587) and peripheral cone dystrophy (PCD; MIM 609021) [7,8,9,10,11,12,13,14,15,16]. OCMD and PCD can be segregated by electrophysiologic responses to full field electroretinography (ffERG) and multifocal electroretinography (mfERG). OCMD displays normal photopic waveforms on ffERG and reduced mfERG responses only at the fovea, which correlates clinically with reduced visual acuities and foveal cone photoreceptor atrophy seen on spectral-domain optical coherence tomography (SDOCT). OCMD is inherited in a dominant fashion and is usually associated with mutations in RP1L1 [17].
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