Biases in the spectral amplitude distribution of a natural scene modulate horizontal size perception.

Introduction: Visual perception is a complex process that involves the analysis of different spatial and temporal features of the visual environment. One critical aspect of this process is adaptation, which allows the visual system to adjust its sensitivity to specific features based on the context of the environment. Numerous theories highlight the significance of the visual scene and its spectral properties in perceptual and adaptation mechanisms. For example, size perception is known to be influenced by the spatial frequency content of the visual scene. Nonetheless, several inquiries still exist, including how specific spectral properties of the scene play a role in size perception and adaptation mechanisms. Methods: In this study, we explore aftereffects on size perception following adaptation to a natural scene with a biased spectral amplitude distribution. Twenty participants had to manually estimate the horizontal size of a projected rectangle after adaptation to three visually biased conditions: vertical-biased, non-biased, and horizontal-biased. Size adaptation aftereffects were quantified by comparing the perceptual responses from the non-biased condition with the vertical- and horizontal-biased conditions. Results: We found size perception shifts which were contingent upon the specific orientation and spatial frequency distribution inherent in the amplitude spectra of the adaptation stimuli. Particularly, adaptation to vertical-biased produced a horizontal enlargement, while adaptation to horizontal-biased generated a decrease in the horizontal size perception of the rectangle. On average, size perception was modulated by 5-6%. Discussion: These findings provide supporting evidence for the hypothesis that the neural mechanisms responsible for processing spatial frequency channels are involved in the encoding and perception of size information. The implications for neural mechanisms underlying spatial frequency and size information encoding are discussed.

L-opsin expression in chickens is similarly reduced with diffusers and negative lenses.

Previous studies have shown that the expression of L- and M-opsins was reduced in chicken retina when eyes were covered with diffusers. The purpose of the current study was to find out whether this is a result of altered spatial processing during development of deprivation myopia or merely a consequence of light attenuation by the diffusers. Therefore, retinal luminances were matched by neutral density filters in fellow eyes that served as controls for diffuser-treated eyes. Furthermore, the effects of negative lenses on opsins expression were studied. Chickens wore diffusers or -7D lenses for a period of 7 days and refractive state and ocular biometry were measured at the beginning and at the end of the experiment. Retinal tissue was extracted from both eyes to quantify L-, M- and S-opsins expression by qRT-PCR. It was found that L-opsin expression was significantly lower in eyes wearing diffusers, compared to fellow eyes covered with neutral density filters. Interestingly, L-opsin was also reduced in eyes wearing negative lenses. In summary, this study shows that L-opsin expression is reduced due to the loss of high spatial frequencies and general contrast reduction in the retinal image, rather than by a decline in retinal luminance. Moreover, the fact that L-opsin was similarly reduced in eyes treated with negative lenses and diffusers suggests the existence of a common pathway for emmetropization, but it could also be just a consequence of reduced high spatial frequencies and lower contrast.

Impact of cone abundancy ratios and light spectra on emmetropization in chickens.

We had previously found that chicken eyes with normal visual experience grow larger when they have more L cones, relative to M cones. It is not known whether also S cone abundancies may affect eye size, whether cone abundancy ratios can also affect the amount of deprivation myopia that is induced by diffusers in front of the eyes, and whether broadband white light with added energy in the blue may reduce the development of deprivation myopia. Therefore, chickens were monocularly treated with diffusers and raised under three different light conditions with increasing amounts of energy in the blue but with matched total illuminance. L, M and S cones were counted in fresh retinal tissues after the experiments. It was found that adding energy in the blue did not significantly inhibit deprivation myopia, nor did it make uncovered eyes more hyperopic. However, more S cones, relative to L cones, were correlated with more hyperopic refractions in eyes with normal vision. M to L, L to S and M to S cone ratios were also correlated with the amount of induced deprivation myopia. Interestingly, in deprivation myopia, the correlations between cone abundancy ratios with refractive states had reverted signs: eyes with more S cones developed more myopia. Since cone abundancy ratios remained correlated in both eyes, no matter whether eyes had normal vision, were deprived or were exposed to different light spectra, they appear genetically determined. We conclude that, among other factors, inherited cone abundancy ratios determine both normal refractive development and deprivation myopia in the chicken while adding more blue light to a broadband light spectrum had no effect.

Interactions of cone abundancies, opsin expression, and environmental lighting with emmetropization in chickens.

We had previously found that M to L cone abundancy ratios in the chicken retina are correlated with vitreous chamber depth and refractive state in chickens eyes, when they have normal visual exposure but not when they develop deprivation myopia. The finding suggests an interaction between cone abundancies and emmetropization. In the current study, we analyzed how stable this correlation was against changes in environmental variables and strain differences. We found that the correlation was preserved in two chicken strains, as long as they were raised in the laboratory facilities and not in the animal facilities of the institute. To determine the reasons for this difference, spectral and temporal lighting parameters were better adjusted in both places, whereas temperature, humidity, food, diurnal lighting cycles and illuminance were already matched. It was also verified that both strains of chickens had the same cone opsin amino acid sequences. The correlation between M to L cone abundancy and ocular biometry is highly susceptible to changes in environmental variables. Yet undetermined differences in lighting parameters were the most likely reasons. Other striking findings were that green cone opsin mRNA expression was downregulated when deprivation myopia developed. Similarly, red opsin mRNA was downregulated when chicks wore red spectacles, which made them more hyperopic. In summary, our experiments show that photoreceptor abundancies, opsin expression, and the responses to deprivation, and therefore emmetropization, are surprisingly dependent on subtle differences in lighting parameters.

Quantification of Growth Factors and Fibronectin in Diverse Preparations of Platelet-Rich Plasma for the Treatment of Ocular Surface Disorders (E-PRP).

Purpose: The purpose of this study was to quantify the presence of growth factors (GFs) and fibronectin in autologous platelet-rich plasma for topical ocular use (E-PRP) comparing their concentration when different preparation and preservation procedures were applied. Methods: E-PRP was prepared with blood from healthy volunteers. The count of platelets, leukocytes, and red blood cells in the whole blood and E-PRP were performed. The concentration of the GFs platelet-derived growth factor BB (PDGF-BB), transforming growth factor ß1 (TGF-ß1), epidermal growth factor (EGF), vascular endothelial growth factor A (VEGF-A), and fibronectin was determined in each of the four procedures applied including fresh, frozen at -20°C for 3 months, fresh-spin, and frozen-spin at -20°C E-PRP samples. Posterior statistical analysis was performed to establish significant differences between groups and between GFs in relation to the amounts of platelets. Results: Platelets in the E-PRP doubled in the number of basal values of whole blood (P ≤ 0.01). The blood cells in the E-PRP decreased drastically in red cells (99%) and also in leukocytes (82%). The concentration of PDGF-BB and EGF was significantly higher (P < 0.01) when the E-PRP samples were frozen at -20°C. However, no significant differences were observed for TGF-ß1, VEGF-A, and fibronectin (P > 0.05). The concentration of GFs in the E-PRP did not necessarily correlate with the number of platelets. Conclusions: Freezing the E-PRP for 3 months at -20°C increased the concentration of important proteins, such as PDGF-BB and EGF, and maintained the levels of others. These findings are essential because treatments, such as E-PRP, used by patients with ocular surface dysfunctions tend to prolong it in time. In addition, subsequent centrifugation of the E-PRP decreased the values of TFG-ß1, but not the other GFs, which would allow adjusting the concentration of TFG-ß1, as necessary. This procedure guarantees their correct conservation and viability. Translational Relevance: This work demonstrates how clinical application can be improved by starting from basic research. The quantification of GFs and fibronectin in platelet-rich plasma (PRP) helps to clarify which is the best mode of preparation and preservation of PRP for clinical applications. This allows to optimize the product that is delivered to the patients as a treatment for the dysfunctions of the ocular surface, guaranteeing that the conservation does not affect at all the quality of the PRP that it is going to be used.

M to L cone ratios determine eye sizes and baseline refractions in chickens.

Following a hypothesis raised by M. and J. Neitz, Seattle, we have tested whether the abundance and the ratio of Long wavelength-sensitive (L) to Middle wavelength-sensitive (M) cones may affect eye size and development of myopia in the chicken. Fourteen chickens were treated with frosted plastic diffusers in front of one eye on day 10 post-hatching for a period of 7 days to induce deprivation myopia. Ocular dimensions were measured by A-scan ultrasonography at the beginning and at the end of the treatment and development of refractive state was tracked using infrared photorefraction. At the end of the treatment period, L and M cone densities and ratios were analyzed in retinal flat mounts of both myopic and control eyes, using the red and yellow oil droplets as markers. Because large numbers of cones were counted (>10000), software was written in Visual C++ for automated cone detection and density analysis. (1) On average, 9.7 ± 1.7D of deprivation myopia was induced in 7 days (range from 6.8D to 13.7D) with an average increase in axial length by 0.65 ± 0.20 mm (range 0.42 mm-1.00 mm), (2) the increase in vitreous chamber depth was correlated with the increase in myopic refractive error, (3) average central M cone densities were 10,498 cells/mm2, and L cone densities 9574 cells/mm2. In the periphery, M cone densities were 6343 cells/mm2 and L cones 5735 cells/mm2 (4) M to L cone ratios were highly correlated in both eyes of each animal (p < 0.01 in all cases), (5) the most striking finding was that ratios of M to L cones were significantly correlated with vitreous chamber depths and refractive states in the control eyes with normal vision, both in the central and peripheral retinas (p < 0.05 to p < 0.01), (6) M to L cone ratios did however not predict the amount of deprivation myopia that could be induced. M and L cone ratios are most likely genetically determined in each animal. The more L cones, the deeper the vitreous chambers and the more myopic were the refractions in eyes. M to L cone ratios may determine the set point of emmetropization and thereby ultimately the probability of becoming myopic. Deprivation myopia was not determined by M to L cone ratios.

Treatment with platelet-rich plasma of surgically related dormant corneal ulcers.

PURPOSE: To assess the effectiveness of autologous platelet-rich plasma for the treatment of dormant corneal ulcers secondary to corneal surgery and unresponsive to conventional treatment. SETTING: VISSUM, Ophthalmology Institute of Alicante, Alicante, Spain. DESIGN: Prospective nonrandomized, observational consecutive study. METHODS: A total of 44 eyes of 28 patients with dormant corneal ulcers secondary to corneal surgery were included in a prospective study and treated with autologous platelet-rich plasma during 6 weeks. Wilcoxon signed-rank test was used to compare the effect of the treatment. RESULTS: In all, 28 patients (65.1%) improved their visual acuity at least one line in Snellen chart, 26 (59.09%) had a decrease in the size of the ulcer or even a total closure, and 40 (90.9%) experienced an improvement in their symptoms. The results are also provided for the four groups of patients (keratoplasty, refractive surgery, cross-linking, and chronic postsurgical corneal edema). CONCLUSION: Platelet-rich plasma eye drops shows to be a good option for the treatment of dormant corneal ulcers secondary to corneal surgery.