The Negative Cone Mosaic: A New Manifestation of the Optical Stiles-Crawford Effect in Normal Eyes.

PURPOSE: The purpose of this study was to describe a previously unreported manifestation of the optical Stiles-Crawford effect (oSCE) in normal eyes. METHODS: In a cohort of 50 normal subjects, the directional reflectance of cones in the retinal periphery was explored by flood-illuminated adaptive optics (FIAO) and optical coherence tomography (OCT). RESULTS: In 32 eyes (64%), off-axis FIAO images of the retinal periphery (∼15-20° from the fovea) showed variably sized patches of hyporeflective dots (called here negative mosaic) coexisting with hyperreflective (positive) cones. In nine cases, shifting the entry pupil toward the optical axis restored the positive cone mosaic, with a point-by-point correspondence between positive and negative mosaics. Rods remained hyperreflective around negative and positive cones. These changes were paralleled by changes of the OCT reflectance of the cone outer segment tips and, to a lesser extent, of the inner/outer segment limit. CONCLUSIONS: By en face FIAO imaging of the retina, the contrast of cones over rods may be strongly dependent on the entry pupil to such an extent that their reflectance is lower than that of rods. We hypothesized that the negative cone mosaic aspect results from the differential Stiles-Crawford effect of cones and rods. Cone reflectance by en face FIAO parallels the reflectance from the cone outer segment tip line and to a lesser extent of the inner/outer segment limit by OCT. Taking this into account, the oSCE is of importance for the interpretation of high-resolution images of photoreceptors. (ClinicalTrials.gov number, NCT01546181.)

High-resolution imaging of gunn's dots.

BACKGROUND: In healthy fundi, glistening whitish dots (so-called Gunn's dots) can often be seen, especially in young subjects. They are commonly attributed to the reflectance of Müller cell's footplates. However, despite their potential interest as biomarkers of retinal diseases, Gunn's dots have received little attention in the scientific literature. METHODS: Scanning laser ophthalmoscope reflectance imaging and adaptive optics infrared flood imaging were performed in 18 healthy subjects (age range, 18-58 years) to analyze the localization, density, and shape of Gunn's dots. RESULTS: Gunn's dots were more easily observed in the midperipheral retina along temporal vessels, although in two subjects, they could be detected in the macula. The reflectance of Gunn's dots showed a strong directional variability, which paralleled that of the inner limiting membrane. The mean (±SD) diameter of Gunn's dots was 13.3 µm (±3.5). Their density peaked at ∼120 per square millimeter and decreased with age to become barely detectable after 50 years. CONCLUSION: Gunn's dots are highly anisotropic structures close to the inner limiting membrane. Their density, size, and age-related decline are closer to the characteristics of hyalocytes than those of Müller cells. Further studies are necessary to progress in the determination of their origin and interest as biomarkers of retinal diseases.