Crowding is the substantial interference of neighboring items on target identification. Crowding with letter stimuli has been studied primarily in the visual periphery, with conflicting results for foveal stimuli. While a cortical locus for peripheral crowding is well established (with a large spatial extent up to half of the target eccentricity), disentangling the contributing factors in the fovea is more challenging due to optical limitations. Here, we used adaptive optics (AO) to overcome ocular aberrations and employed high-resolution stimuli to precisely characterize foveal lateral interactions with high-contrast letters flanked by letters. Crowding was present, with a maximal edge-to-edge interference zone of 0.75-1.3 minutes at typical unflanked performance levels. In agreement with earlier foveal contour interaction studies, performance was non-monotonic, revealing a recovery effect with proximal flankers. Modeling revealed that the deleterious effects of flankers can be described by a single function across stimulus sizes when the degradation is expressed as a reduction in sensitivity (expressed in Z-score units). The recovery, however, did not follow this pattern, likely reflecting a separate mechanism. Additional analysis reconciles multiple results from the literature, including the observed scale invariance of center-to-center spacing, as well as the size independence of edge-to-edge spacing.

The wavelength of light that appears unique yellow is surprisingly consistent across people even though the ratio of middle (M) to long (L) wavelength sensitive cones is strikingly variable. This observation has been explained by normalization to the mean spectral distribution of our shared environment. Our purpose was to reconcile the nearly perfect alignment of everyone's unique yellow through a normalization process with the striking variability in unique green, which varies by as much as 60 nm between individuals. The spectral location of unique green was measured in a group of volunteers whose cone ratios were estimated with a technique that combined genetics and flicker photometric electroretinograms. In contrast to unique yellow, unique green was highly dependent upon relative cone numerosity. We hypothesized that the difference in neural architecture of the blue-yellow and red-green opponent systems in the presence of a normalization process creates the surprising dependence of unique green on cone ratio. We then compared the predictions of different theories of color vision processing that incorporate L and M cone ratio and a normalization process. The results of this analysis reveal that—contrary to prevailing notions--postretinal contributions may not be required to explain the phenomena of unique hues.

Objective: To evaluate the association between retinopathy of prematurity and vitreous findings in premature infants detected by handheld spectral-domain optical coherence tomography.Design: Prospective, observational cohort study.Participants: Consecutive sample of 92 premature infants requiring retinopathy of prematurity screening at two academic neonatal intensive care units, between July 2015 and March 2018. Methods:Infants underwent handheld spectral domain optical coherence tomography at the time of routine retinopathy of prematurity examinations. Two masked, trained graders analyzed right eye vitreoretinal findings including semi-automated quantification of punctate hyperreflective vitreous opacities within 5 foveal/parafoveal B-scans (Vitreous Opacity Ratio). Main Outcome Measures:Excluding post-treatment data, vitreous findings were compared to clinical retinopathy of prematurity diagnoses.Results: Agreement between image graders for all vitreoretinal findings was 91% (kappa=0.86 [95% confidence interval, 0.82-0.90], P<0.001). Among 92 infants undergoing 280 imaging sessions (52% male, mean gestational age 28.3±2.8 weeks, mean birthweight 1014.5±285.0 grams), 36/92 (39%) developed retinopathy of prematurity. Punctate hyperreflective vitreous opacities were identified in 61/92 (66%) infants. The presence of punctate hyperreflective vitreous opacities at least once was associated with a diagnosis of retinopathy of prematurity (62% vs. 29% without opacities, P=0.003), maximum retinopathy of prematurity stage (P=0.001), pre-plus or plus disease (24% vs. 5%, P=0.005), and type 1 disease (14% vs. 2%, P=0.03).

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