Structural photoreceptor abnormalities and an area of central sparing found.
Reviewed by Ethan K. Sobol, MD, and Justin Migacz, PhD.
Adaptive optics scanning laser ophthalmoscopy (AOSLO) is helping physicians understand more about the macular phenotype of fundus albipunctatus, a rare congenital retinal disease that negatively affects the photoreceptor cells. The disease causes night blindness and as it advances, color vision and central vision disturbances.
Using AOSLO, researchers described the structural changes in this macular phenotype of a novel RDH5 mutation in a patient with fundus albipunctatus,1 reported Ethan Sobol, MD, an Ophthalmology Resident, and Justin Migacz, PhD, a postdoctoral fellow at the Icahn School of Medicine at Mount Sinai, New York.
A 62-year-old man had been diagnosed with Stargardt’s disease about 10 years previously. He had had night blindness for an extended duration of time. He underwent genetic testing and imaging studies. The visual acuity was 20/25 bilaterally and his dark adaptation was poor.
A fundus examination showed “well circumscribed bilateral perifoveal mottling and atrophy in both eyes.” Investigators also observed bilateral discrete white-yellow flecks beyond the vascular arcades out to the far periphery.
Optical coherence tomography (OCT) and OCT angiography abnormalities, respectively, showed abnormalities in the perifoveal photoreceptors and outer retina and patchy areas of nonperfusion in the choriocapillaris with normal retinal vasculature.
AOSLO went steps further and showed bilateral macular abnormalities as well as a small amount of normal cones with small central islands in both eyes that was unaffected. In the macula, the rods were larger and more irregular. Importantly, “non-confocal split detection AOSLO revealed the presence of cone inner segments in dark regions of confocal imaging, indicating some degree of photoreceptor preservation,” the investigators reported.
The lesson here is that in this case it was important to differentiate Stargardt’s disease from fundus albipunctatus because of the very different prognoses of the 2 disorders. The vision of patients with Stargardt’s disease typically deteriorates over time. In contrast, fundus albipunctatus generally affects night vision, with visual acuity remaining stable in most cases.
In commenting on their findings, the investigators said, “…while the patient’s original diagnosis of Stargardt’s disease was upended by genetic testing, the AOSLO findings are helpful for explaining the patient’s clinical presentation. Previous studies using AOSLO in Stargardt’s disease have revealed increased cone and rod spacing, with reduced foveal cone density and enlarged cone size, and dark cones thought to be associated with foreshortened outer segments.2 These findings are similar to our patient’s photoreceptor characteristics on AOSLO, except for the profound sparing observed in the central fovea. Indeed, AOSLO appears to be better able to characterize the photoreceptor status than traditional imaging modalities.”
They also suggested that routine AO may play a role in early diagnosis of the disease and a better understanding of the physiology may lead to a future treatment.