Individual set-point and gain of emmetropization in chickens

AbstractDuring the developmental process of emmetropization evidence shows that visual feedback guides the eye as it approaches a refractive state close to zero, or slightly hyperopic. How this “set-point” is internally defined, in the presence of continuous shifts of the focal plane with different viewing distances and accommodation, remains unclear. Minimizing defocus blur over time should produce similar end-point refractions in different individuals. However, we found that individual chickens display considerable variability in their set-point refractive states, despite that they all had the same visual experience. This variability is not random since the refractions in both eyes were highly correlated – even though it is known that they can emmetropize independently. Furthermore, if chicks underwent a period of experimentally induced ametropia, they returned to their individual set-point refractions during recovery (correlation of the refractions before treatment versus after recovery: n=19 chicks, 38 eyes, left eyes: slope 1.01, R=0.860; right eyes: slope 0.85, R=0.610, p<0.001, linear regression). Also, the induced deprivation myopia was correlated in both eyes (n=18 chicks, 36 eyes, p<0.01, orthogonal regression). If chicks were treated with spectacle lenses, the compensatory changes in refraction were, on average, appropriate but individual chicks displayed variable responses. Again, the refractions of both eyes remained correlated (negative lenses, n=18 chicks, 36 eyes, slope 0.89, R=0.504, p<0.01, positive lenses: n=21 chicks, 42 eyes, slope 1.14, R=0.791, p<0.001). The amount of deprivation myopia that developed in two successive treatment cycles, with an intermittent period of recovery, was not correlated; only vitreous chamber growth was almost significantly correlated in both cycles (n=7 chicks, 14 eyes; p<0.05). The amounts of ametropia and vitreous chamber changes induced in two successive cycles of treatment, first with lenses and then with diffusers, were also not correlated, suggesting that the “gains of lens compensation” are different from those in deprivation myopia. In summary, (1) there appears to be an endogenous, possibly genetic, definition of the set-point of emmetropization in each individual, which is similar in both eyes, (2) visual conditions that induce ametropia produce variable changes in refractions, with high correlations between both eyes, (3) overall, the “gain of emmetropization” appears only weakly controlled by endogenous factors

Repeatability of automated vessel density measurements using optical coherence tomography angiography

AIMS To determine the repeatability of optical coherence tomography angiography (OCT-A)-derived automated vessel density measurements in the superficial retinal layer (SRL) and deep retinal layer (DRL) in healthy individuals. METHODS 41 eyes of 21 healthy individuals were included in this study. OCT-A was performed using the NIDEK RS-3000 Advance with prototype OCT-A software. Each subject underwent two scanning sessions with 5-10 min in between. En face images of the retinal vasculature were generated using the default segmentation for SRL and DRL. Automated vessel density measurements were compared between the two sessions. The intraclass correlation coefficients (ICCs) and coefficient of repeatability were used as a measure for repeatability. RESULTS The mean±SD age of the subjects was 36.8±7.5 years. Overall vessel density measured in the first and second session was 19.43±3.10 and 19.72±3.78 for the SRL, and 34.67±1.801 and 34.55±1.64 for the DRL, respectively. The mean difference in vessel density between sessions was -0.3 (95% CI 3.3 to -3.9) for the SRL and 0.1 (95% CI 2.6 to -2.5) for the DRL. The two measurements were highly correlated with an ICC=0.90 (p=0.33) for the SRL and 0.83 (p=0.589) for the DRL. The coefficient of variation was 0.052 for the SRL and 0.02 for the DRL. CONCLUSIONS Commercial automated vessel density measurements using OCT-A showed excellent repeatability in healthy individuals. Although repeatability will also need to be established in the setting of disease, the level of reproducibility should be useful for assessing the significance of differences in capillary density over time or under different conditions

Topographic distribution of choriocapillaris flow deficits in healthy eyes.

PURPOSE:To evaluate the topographic distribution of the choriocapillaris (CC) flow deficits in a population of healthy subjects. METHODS:Using a swept-source optical-coherence tomography angiography (SS-OCTA) device, two repeated volume 6 x 6 mm and 3 x 3 mm scans were acquired in healthy subjects at the Doheny-UCLA Eye Centers. The en-face CC angiogram was binarized and analyzed for percentage of flow deficits (FD%) using a grid of progressive, concentric rings covering a circular area with a diameter of 2.5 mm (in the 3 x 3 mm scans) and 5 mm (in the 6 x 6 mm scans). The FD% for each ring was plotted against the distance from the fovea. The linear trendline of the resulting curve was analyzed and the slope (m) and intercept (q) were computed. RESULTS:Seventy-five eyes of 75 subjects were enrolled and divided into three subgroups based on age (year ranges: 21-40, 41-60 and 61-80). For the entire cohort and within each subgroup, there was a significant association between distance from the fovea and FD% in both 3X3 mm and 6X6 mm scans, with flow deficits increasing with closer proximity to the foveal center. Age was a significant predictor for both m and q for both scan patterns, with older subjects showing a steeper slope. CONCLUSIONS:In SS-OCTA images, the topographic distribution of CC flow deficits varies with distance from the fovea and age. In particular, the FD% tends to decrease from the fovea towards the periphery, with a steeper decline with advancing age. These normal trends may need to be accounted for in future studies of the CC in disease

Evaluation of the corneal epithelium in non-Sjögren’s and Sjögren’s dry eyes: an in vivo confocal microscopy study using HRT III RCM

Abstract Background The corneal epithelium is directly affected in dry eye syndrome. Thus, we attempted to describe the morphological features and evaluate the cellular density within the corneal epithelial layers in patients with non-Sjögren’s (NSDE) and Sjögren’s syndrome dry eyes (SSDE) by in vivo confocal microscopy (IVCM). Methods Central cornea was prospectively imaged by IVCM in 68 clinically diagnosed aqueous tear-deficient dry eyes and 10 healthy age-matched control eyes. Morphological characteristics of corneal epithelial layers and cellular densities were evaluated by four trained graders from the Doheny Eye Institute. Results Corneal epithelium in dry eyes presents morphological changes such as areas of enlarged and irregular shaped cells. In comparison with controls, the density of superficial epithelial cells was decreased in both the NSDE (P  0.05), but was lower in the SSDE group (P < 0.01); the density of the inner layer of wing cells was decreased in both the NSDE (P < 0.05) and SSDE groups (P < 0.01) and the density of basal epithelial cells was lower in both the NSDE (P < 0.01) and SSDE groups (P = 0.01). For all cell counts, the interclass correlation coefficient showed good agreement between graders (ICC =0.75 to 0.93). Conclusions IVCM represents a reliable technique for examining the corneal epithelial microstructural changes associated with dry eyes, as well as for objectively and reproducibly quantifying cell densities within all corneal epithelial layers