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External limiting membrane thicker in young Stargardt's patients
The thickness of the external limiting membrane was significantly greater in Stargardt's patients than in unaffected controls, according to a study published electronically in Investigative Ophthalmology & Visual Science.
Lee and colleagues also reported that imaging revealed hyper-reflective deposits in the outer nuclear layer of every patient.
Researchers evaluated 26 patients younger than 20 years who were genetically confirmed to have the ABCA4 allele to have Stargardt’s disease (STGD1). They also evaluated 30 control patients unaffected by the disease and age-matched to the Stargardt's participants.
Researchers collected and analyzed spectral domain-optical coherence tomography and fundus images with a Spectralis HRA+OCT (Heidelberg Engineering); fundus autofluorescence and near-infrared reflectance images with a confocal scanning-laser ophthalmoscope (cSLO, Heidelberg Retina Angiograph 2, Heidelberg); color fundus photography images with a FF 450plus Fundus Camera (Carl Zeiss Meditec AG); and electroretinograms with the Diagnosys Espion Electrophysiology System (Diagnosys LLC) for one to four visits for each patient.
"In all examined patients, an observable thickening of the ELM and increased discernibility was evident in the macula, particularly in areas of relatively intact photoreceptors and RPE," the authors stated. "In other areas, this observation was also concurrent with other STGD1-associated findings such as early pisciform flecks, local hyper-autofluorescence and centrally confined areas of hypo-autofluorescence. One case, however, exhibited the abnormal ELM without any other apparent pathology on funduscopy and was asymptomatic."
Results also showed that four patients "exhibited an unusual foveal lesion characterized by an isolated concave protuberance or bulging of the ELM that was thickened and hyper-reflective and that encased a small area of inner segment ellipsoid band, despite surrounding regions of atrophic changes," which was associated with areas of hypo-autofluorescence.
Jerome Sherman, OD, FAAO, a Primary Care Optometry News Editorial Board member, discussed the possibility of a biomarker for Stargardt's last year in PCON after evaluating several young children.
Sherman found a thickening of the ELM through the use of SD-OCT images.
“The outer nuclear layer above the ELM is normally composed of dense and closely packed nuclei of the cones and rods and is hence hyporeflective,” he told PCON. “As the nuclei degenerate, they are less densely packed and occupy a larger space. But as this occurs, the entire outer nuclear layer becomes less hyporeflective and more hyper-reflective.”
In the interview, Sherman noted that a biomarker for Stargardt's would allow earlier diagnoses, the development of early interventions and a way to observe treatment efficacy.
In a recent email to PCON, Sherman also noted that the biomarker is present in children as early as 4 years old who have normal vision and a normal-looking retina. – by Chelsea Frajerman
Disclosures: The study authors report no conflicts of interest in this work. Sherman lectures/consults for Topcon, Zeiss and Optovue with regard to SD-OCT and Optos with regard to ultra-widefield color and autofluorescence technology.