Dynamic changes in ocular shape during human development and its implications for retina fovea formation.

The human fovea is known for its distinctive pit-like appearance, which results from the displacement of retinal layers superficial to the photoreceptors cells. The photoreceptors are found at high density within the foveal region but not the surrounding retina. Efforts to elucidate the mechanisms responsible for these unique features have ruled out cell death as an explanation for pit formation and changes in cell proliferation as the cause of increased photoreceptor density. These findings have led to speculation that mechanical forces acting within and on the retina during development underly the formation of foveal architecture. Here we review eye morphogenesis and retinal remodeling in human embryonic development. Our meta-analysis of the literature suggests that fovea formation is a protracted process involving dynamic changes in ocular shape that start early and continue throughout most of human embryonic development. From these observations, we propose a new model for fovea development.

Melanopsin in the human and chicken choroid.

The choroid embedded in between retina and sclera is essential for retinal photoreceptor nourishment, but is also a source of growth factors in the process of emmetropization that converts retinal visual signals into scleral growth signals. Still, the exact control mechanisms behind those functions are enigmatic while circadian rhythms are involved. These rhythms are attributed to daylight influences that are melanopsin (OPN4) driven. Recently, OPN4-mRNA has been detected in the choroid, and while its origin is unknown we here seek to identify the underlying structures using morphological methods. Human and chicken choroids were prepared for single- and double-immunohistochemistry of OPN4, vasoactive intestinal peptide (VIP), substance P (SP), CD68, and α-smooth muscle actin (ASMA). For documentation, light-, fluorescence-, and confocal laser scanning microscopy was applied. Retinal controls proved the reliability of the OPN4 antibody in both species. In humans, OPN4 immunoreactivity (OPN4-IR) was detected in nerve fibers of the choroid and adjacent ciliary nerve fibers. OPN4+ choroidal nerve fibers lacked VIP, but were co-localized with SP. OPN4-immunoreactivity was further detected in VIP+/SP+ intrinsic choroidal neurons, in a hitherto unclassified CD68-negative choroidal cell population thus not representing macrophages, as well as in a subset of choroidal melanocytes. In chicken, choroidal nerve fibers were OPN4+, and further OPN4-IR was detected in clustered suprachoroidal structures that were not co-localized with ASMA and therefore do not represent non-vascular smooth-muscle cells. In the choroidal stroma, numerous cells displayed OPN4-IR, the majority of which was VIP-, while a few of those co-localized with VIP and were therefore classified as avian intrinsic choroidal neurons. OPN4-immunoreactivity was absent in choroidal blood vessels of both species. In summary, OPN4-IR was detected in both species in nerve fibers and cells, some of which could be identified (ICN, melanocytes in human), while others could not be classified yet. Nevertheless, the OPN4+ structures described here might be involved in developmental, light-, thermally-driven or nociceptive mechanisms, as known from other systems, but with respect to choroidal control this needs to be proven in upcoming studies.

Defocus-induced spatial changes in choroidal thickness of chicks observed by wide-field swept-source OCT.

Choroid has been claimed to be of importance during ocular development. However, how the choroid responds spatially to different visual cues has not been fully understood. The aim of this study was to investigate defocus-induced spatial changes in choroidal thickness (ChT) in chicks. Eight 10-day-old chicks were fitted monocularly with -10 D or +10 D lenses (day 0), which were removed seven days later (day 7). The ChT was measured on days 0, 7, 14, and 21 using wide-field swept-source optical coherence tomography (SS-OCT) and analyzed with custom-made software. Comparisons of the ChT in the central (1 mm), paracentral (1-3 mm), and peripheral (3-6 mm) ring areas and the ChT in the superior, inferior, nasal, and temporal regions were conducted. Axial lengths and refractions were also evaluated. In the negative lens group, the global ChT of the treated eyes was significantly less than that of the fellow eyes on day 7 (interocular difference: 179.28 ± 25.94 µm, P = 0.001), but thicker on day 21 (interocular difference: 241.80 ± 57.13 µm, P = 0.024). These changes were more pronounced in the central choroid. The superior-temporal choroid changed more during induction but less during recovery. In the positive lens group, the ChT of both eyes increased on day 7 and decreased on day 21, with most changes occurring in the central region, too. The inferior-nasal choroid of the treated eyes changed more during induction but less during recovery. These results provide evidence for regionally asymmetric characteristics of the choroidal response to visual cues and insights into the underlying mechanisms of emmetropization.

The effects of ambient narrowband long-wavelength light on lens-induced myopia and form-deprivation myopia in tree shrews.

Here we examine the effects of ambient red light on lens-induced myopia and diffuser-induced myopia in tree shrews, small diurnal mammals closely related to primates. Starting at 24 days of visual experience (DVE), seventeen tree shrews were reared in red light (624 ± 10 or 634 ± 10 nm, 527-749 human lux) for 12-14 days wearing either a -5D lens (RL-5D, n = 5) or a diffuser (RLFD, n = 5) monocularly, or without visual restriction (RL-Control, n = 7). Refractive errors and ocular dimensions were compared to those obtained from tree shrews raised in broad-spectrum white light (WL-5D, n = 5; WLFD, n = 10; WL Control, n = 7). The RL-5D tree shrews developed less myopia in their lens-treated eyes than WL-5D tree shrews at the end of the experiment (-1.1 ± 0.9D vs. -3.8 ± 0.3D, p = 0.007). The diffuser-treated eyes of the RLFD tree shrews were near-emmetropic (-0.3 ± 0.6D, vs. -5.4 ± 0.7D in the WLFD group). Red light induced hyperopia in control animals (RL-vs. WL-Control, +3.0 ± 0.7 vs. +1.0 ± 0.2D, p = 0.02), the no-lens eyes of the RL-5D animals, and the no-diffuser eyes of the RLFD animals (+2.5 ± 0.5D and +2.3 ± 0.3D, respectively). The refractive alterations were consistent with the alterations in vitreous chamber depth. The lens-induced myopia developed in red light suggests that a non-chromatic cue could signal defocus to a less accurate extent, although it could also be a result of "form-deprivation" caused by defocus blur. As with previous studies in rhesus monkeys, the ability of red light to promote hyperopia appears to correlate with its ability to retard lens-induced myopia and form-deprivation myopia, the latter of which might be related to non-visual ocular mechanisms.

The effects of intensity, spectral purity and duty cycle on red light-induced hyperopia in tree shrews.

INTRODUCTION: There have recently been several clinical studies suggesting that brief periods of exposure to red light (repeated low-level red light, 'RLRL') may produce a dramatic anti-myopia effect, calling for further investigations into its therapeutic parameters. Unfortunately, many experimental species used in refractive studies develop myopia in response to this wavelength. Tree shrews are the only animal model other than rhesus monkeys that consistently exhibit hyperopic responses to ambient red light. Here, tree shrews were used to study the influence of the spectral purity, duty cycle and intensity of red light on its anti-myopic effect. METHODS: Juvenile tree shrews (Tupaia belangeri) were raised from 24 to 35 days after eye opening under ambient lighting that was: standard white colony fluorescent light; pure narrow band red light of either 600, 50-100 or 5 lux; red light that was diluted with 10% white light (by lux) or 50% white and 2 s of pure red light that alternated with 2 s of pure white light (50% duty cycle). Refractive measures were taken with a NIDEK ARK-700 autorefractor and axial dimensions with a LenStar LS-900 Axial Biometer. RESULTS: The pro-hyperopia effect of ambient red light was greatly reduced by even small amounts of concurrent white light 'contamination', but remained robust if 2-s periods of pure white light alternated with 2 s of red. Finally, the hyperopic effect of red light was maintained at reduced luminance levels in the 50-100 lux range and only failed at 5 lux. CONCLUSIONS: These results have implications for understanding the mechanisms by which ambient red light affects refractive development, and possibly also for clinical therapies using RLRL. Nevertheless, it remains to be determined if the mechanism of the current clinical RLRL therapy is the same as that operating on tree shrews in ambient red light.

Parasympathetic innervation of emmetropization.

Emmetropization is affected by the temporal parameters of visual stimulation and the spectral composition of light, as well as by autonomic innervation. The goal of the current experiments is to test the hypothesis that different types of visual stimulation interact with ocular innervation in the process of emmetropization. For that, selective lesions of the autonomic nervous system were performed in chickens: involving transection of parasympathetic input to the eye from either the ciliary ganglion, innervating accommodation and pupil responses (CGX; n = 32), or pterygopalatine ganglion, innervating choroidal blood vessels and cornea (PPGX; n = 26). After 1 week of recovery, chicks were exposed to sinusoidally modulated light (3 days, 2 Hz, 680 lux) that was either achromatic (black to white [RGB], or black to yellow [RG]), or chromatic (blue to yellow [B/Y] or red to green [R/G]). Exposure to light stimulation was followed by ocular biometry (Lenstar and a Hartinger refractometer). Surgical conditions revealed a small reduction in anterior chamber depth with CGX but no other significant changes in ocular biometry/refraction under standard light conditions. With RGB achromatic stimulation, CGX eyes produced an effect on ocular components, with a further reduction in anterior chamber depth and an increase in vitreous chamber depth, while RG stimulation showed no effect. No effect was detected in PPGX under both achromatic protocols. With chromatic stimulation, CGX with R/G modulation increased eye length, while PPGX with B/Y modulation decreased eye length. We conclude that the two different types of parasympathetic innervations have antagonistic effects on eye growth and the anterior eye when challenged with the appropriate stimulus, with possible implications for the role of choroidal blood flow in emmetropization.

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.

Effects of morning and evening exposures to blue light of varying illuminance on ocular growth rates and ocular rhythms in chicks.

Recent evidence indicates that moderate levels of blue light are sufficient to suppress the nighttime rise in serum melatonin in humans, suggesting that luminous screens may be deleterious to sleep cycles and to other functions. Little is known however, about the effects of exposures to blue light on ocular physiology. We tested the effects of transient blue light exposures of various illuminances on ocular growth rates and ocular rhythms in chicks. 10-day old chicks were exposed to narrow band blue light (460 nm) of specific illuminance for 4 h in the evening (ZT8-ZT12) or the morning (ZT0-ZT4) for 9 days; for the remainder of the day they were in white light (588 lux). For the evening, four illuminances were tested: 0.15 lux (n = 15), 200 lux (radiometrically matched to white controls; n = 16), 600 lux (photometrically matched to white controls; n = 15) or 1000 lux (n = 8). The 600 lux condition was also tested using a 2-h duration (n = 8). The 200 and 600 lux conditions were extended to 14 and 21 days (n = 8 each). For morning exposures, 200 lux (n = 9), 600 lux (n = 9) and 1000 lux (n = 8) were tested. Controls remained in white light (n = 23). Ocular dimensions were measured by A-scan ultrasonography on days 1 and 9 to assess growth rates. On day 8 or 9, measurements were made at 6-h intervals over 24 h starting at noon to assess rhythm parameters. Evening exposure to blue light stimulated ocular growth rates relative to controls for all except the bright condition (0.15 lux, 200 lux, 600 lux vs bright and white respectively: 845 µm, 838 µm, 898 µm vs 733 µm and 766 µm; p < 0.05 for all comparisons). 2 h exposures to 600 lux were similarly effective (915 µm vs 766 µm; p < 0.05). Morning exposures only resulted in growth stimulation for the 200 lux condition (200 lux vs white: 884 µm vs 766 µm; p < 0.05). Furthermore, for this group only, growth of the anterior chamber had a significant contribution to the overall effect (vs white: p < 0.05), and choroids showed significant thickening. For evening exposures to 200 and 600 lux, the growth stimulatory effect lasted for 14 days (p = 0.01); by 21 days only the 600 lux group still differed (p < 0.0001). Evening exposures caused circadian disruptions in the choroidal thickness rhythms, and morning exposures disrupted both axial and choroidal rhythms. Exposure to 4 h of blue light at lower illuminances (less than 1000 lux) at transition times of lights-on and lights-off stimulates ocular growth rates and affects ocular rhythms in chicks, suggesting that such exposures may be deleterious to emmetropization in children.

Genetic network regulating visual acuity makes limited contribution to visually guided eye emmetropization.

During postnatal development, the eye undergoes a refinement process whereby optical defocus guides eye growth towards sharp vision in a process of emmetropization. Optical defocus activates a signaling cascade originating in the retina and propagating across the back of the eye to the sclera. Several observations suggest that visual acuity might be important for optical defocus detection and processing in the retina; however, direct experimental evidence supporting or refuting the role of visual acuity in refractive eye development is lacking. Here, we used genome-wide transcriptomics to determine the relative contribution of the retinal genetic network regulating visual acuity to the signaling cascade underlying visually guided eye emmetropization. Our results provide evidence that visual acuity is regulated at the level of molecular signaling in the retina by an extensive genetic network. The genetic network regulating visual acuity makes relatively small contribution to the signaling cascade underlying refractive eye development. This genetic network primarily affects baseline refractive eye development and this influence is primarily facilitated by the biological processes related to melatonin signaling, nitric oxide signaling, phototransduction, synaptic transmission, and dopamine signaling. We also observed that the visual-acuity-related genes associated with the development of human myopia are chiefly involved in light perception and phototransduction. Our results suggest that the visual-acuity-related genetic network primarily contributes to the signaling underlying baseline refractive eye development, whereas its impact on visually guided eye emmetropization is modest.

Spectral composition of artificial illuminants and their effect on eye growth in chicks.

In broadband light, longitudinal chromatic aberration (LCA) provides emmetropization signals from both wavelength defocus and the resulting chromatic cues. Indoor illuminants vary in their spectral output, potentially limiting the signals from LCA. Our aim is to investigate the effect that artificial illuminants with different spectral outputs have on chick emmetropization with and without low temporal frequency modulation. In Experiment 1, two-week-old chicks were exposed to 0.2 Hz, square-wave luminance modulation for 3 days. There were 4 spectral conditions: LED strips that simulated General Electric (GE) LED "Soft" (n = 13), GE LED "Daylight" (n = 12), a novel "Equal" condition (n = 12), and a novel "High S" condition (n = 10). These conditions were all tested at a mean level of 985 lux. In Experiment 2, the effect of intensity on the "Equal" condition was tested at two other light levels (70 lux: n = 10; 680 lux: n = 7). In Experiment 3, the effect of temporal modulation on the "Equal" condition was tested by comparing the 0.2 Hz condition with 0 Hz (steady). Significant differences were found in axial growth across lighting conditions. At 985 lux, birds exposed to the "Equal" condition showed a greater reduction in axial growth (both p < 0.01) and a greater hyperopic shift compared to "Soft" and "Daylight" (both p < 0.01). The "High S" birds experienced more axial growth compared to "Equal" (p < 0.01) but less than in "Soft" and "Daylight" (p < 0.01). Axial changes in "Equal" were only observed at 985 lux with 0.2 Hz temporal modulation, and not with lower light levels or steady light. We conclude that axial growth and refraction were dependent on the lighting condition in a manner predicted by wavelength defocus signals arising from LCA.

Contribution of M-opsin-based color vision to refractive development in mice.

M-opsin, encoded by opn1mw gene, is involved in green-light perception of mice. The role of M-opsin in emmetropization of mice remains uncertain. To answer the above question, 4-week-old wild-type (WT) mice were exposed to white light or green light (460-600 nm, a peak at 510 nm) for 12 weeks. Refractive development was estimated biweekly. After treatment, retinal function was assessed using electroretinogram (ERG). Dopamine (DA) in the retina was evaluated by high-performance liquid chromatography, M-opsin and S-opsin protein levels by Western blot and ELISA, and mRNA expressions of opn1mw and opn1sw by RT-PCR. Effects of M-opsin were further verified in Opn1mw-/- and WT mice raised in white light for 4 weeks. Refractive development was examined at 4, 6, and 8 weeks after birth. The retinal structure was estimated through hematoxylin and eosin staining (H&E) and transmission electron microscopy (TEM). Retinal wholemounts from WT and Opn1mw-/- mice were co-immunolabeled with M-opsin and S-opsin, their distribution and quantity were then assayed by immunofluorescence staining (IF). Expression of S-opsin protein and opn1sw mRNA were determined by Western blot, ELISA, or RT-PCR. Retinal function and DA content were analyzed by ERG and liquid chromatography tandem-mass spectrometry (LC-MS/MS), respectively. Lastly, visual cliff test was used to evaluate the depth perception of the Opn1mw-/- mice. We found that green light-treated WT mice were more myopic with increased M-opsin expression and decreased DA content than white light-treated WT mice after 12-week illumination. No electrophysiologic abnormalities were recorded in mice exposed to green light compared to those exposed to white light. A more hyperopic shift was further observed in 8-week-old Opn1mw-/- mice in white light with lower DA level and weakened cone function than the WT mice under white light. Neither obvious structural disruption of the retina nor abnormal depth perception was found in Opn1mw-/- mice. Together, these results suggested that the M-opsin-based color vision participated in the refractive development of mice. Overexposure to green light caused myopia, but less perception of the middle-wavelength components in white light promoted hyperopia in mice. Furthermore, possible dopaminergic signaling pathway was suggested in myopia induced by green light.

Topically instilled caffeine selectively alters emmetropizing responses in infant rhesus monkeys.

Oral administration of the adenosine receptor (ADOR) antagonist, 7-methylxanthine (7-MX), reduces both form-deprivation and lens-induced myopia in mammalian animal models. We investigated whether topically instilled caffeine, another non-selective ADOR antagonist, retards vision-induced axial elongation in monkeys. Beginning at 24 days of age, a 1.4% caffeine solution was instilled in both eyes of 14 rhesus monkeys twice each day until the age of 135 days. Concurrent with the caffeine regimen, the monkeys were fitted with helmets that held either -3 D (-3D/pl caffeine, n = 8) or +3 D spectacle lenses (+3D/pl caffeine, n = 6) in front of their lens-treated eyes and zero-powered lenses in front of their fellow-control eyes. Refractive errors and ocular dimensions were measured at baseline and periodically throughout the lens-rearing period. Control data were obtained from 8 vehicle-treated animals also reared with monocular -3 D spectacles (-3D/pl vehicle). In addition, historical comparison data were available for otherwise untreated lens-reared controls (-3D/pl controls, n = 20; +3D/pl controls, n = 9) and 41 normal monkeys. The vehicle controls and the untreated lens-reared controls consistently developed compensating axial anisometropias (-3D/pl vehicle = -1.44 ± 1.04 D; -3D/pl controls = -1.85 ± 1.20 D; +3D/pl controls = +1.92 ± 0.56 D). The caffeine regime did not interfere with hyperopic compensation in response to +3 D of anisometropia (+1.93 ± 0.82 D), however, it reduced the likelihood that animals would compensate for -3 D of anisometropia (+0.58 ± 1.82 D). The caffeine regimen also promoted hyperopic shifts in both the lens-treated and fellow-control eyes; 26 of the 28 caffeine-treated eyes became more hyperopic than the median normal monkey (mean (±SD) relative hyperopia = +2.27 ± 1.65 D; range = +0.31 to +6.37 D). The effects of topical caffeine on refractive development, which were qualitatively similar to those produced by oral administration of 7-MX, indicate that ADOR antagonists have potential in treatment strategies for preventing and/or reducing myopia progression.

Temporal color contrast guides emmetropization in chick.

As a result of longitudinal chromatic aberration (LCA), longer wavelengths are blurred when shorter wavelengths are in focus, and vice versa. As a result, LCA affects the color and temporal aspects of the retinal image with hyperopic defocus. In this experiment, we investigated how the sensitivity to temporal color contrast affects emmetropization. Ten-day-old chicks were exposed for three days to sinusoidal color modulation. The modulation was either blue/yellow flicker (BY) (n = 57) or red/green flicker (RG) (n = 60) simulating hyperopic defocus with and without a blue light component. The color contrasts tested were 0.1, 0.2, 0.3, 0.4, 0.6, and 0.8 Michelson contrast. The mean illuminance of all stimuli was 680 lux. Temporal modulation was either of a high (10 Hz) or low (0.2 Hz) temporal frequency. To test the role of short- and double-cone stimulation, an additional condition silenced these cones in RG_0.4 (D-) and was compared with RG_0.4 (D+) (n = 14). Changes in ocular components and refractive error were measured using Lenstar and a photorefractometer. With high temporal frequency BY representing an in-focus condition for shorter-wavelengths, we found that high temporal frequency BY contrast was positively correlated with vitreous expansion (R2 = 0.87, p < 0.01), expanding the vitreous to compensate for hyperopic defocus. This expansion was offset by low temporal frequency RG, which represented blurred longer wavelengths. The reduction in vitreous expansion in RG_0.4, was enhanced in D+ compared to D- (p < 0.001), indicating a role for short- and/or double-cones. With high temporal frequency RG representing an in-focus condition for longer-wavelengths, we found that high temporal frequency RG contrast was also positively correlated with a linear increase in vitreous chamber depth (R2 = 0.84, p < 0.01) and eye length (R2 = 0.30, p ≤ 0.05), required to compensate for hyperopic defocus, but also with RG sensitive choroidal thickening (R2 = 0.18: p < 0.0001). These increases in the vitreous and eye length were enhanced with D+ compared to D- (p = 0.003) showing the role of short- and double-cones in finessing the vitreous response to hyperopic defocus. Overall, the increase in vitreous chamber depth in RG was offset by reduced expansion in BY, indicating sensitivity to the shorter focal length of blue light and wavelength defocus. Predictable changes in cone contrast and temporal frequency of the retinal image that occur with LCA and defocus result in homeostatic control of emmetropization.

Functional integration of eye tissues and refractive eye development: Mechanisms and pathways.

Refractive eye development is a tightly coordinated developmental process. The general layout of the eye and its various components are established during embryonic development, which involves a complex cross-tissue signaling. The eye then undergoes a refinement process during the postnatal emmetropization process, which relies heavily on the integration of environmental and genetic factors and is controlled by an elaborate genetic network. This genetic network encodes a multilayered signaling cascade, which converts visual stimuli into molecular signals that guide the postnatal growth of the eye. The signaling cascade underlying refractive eye development spans across all ocular tissues and comprises multiple signaling pathways. Notably, tissue-tissue interaction plays a key role in both embryonic eye development and postnatal eye emmetropization. Recent advances in eye biometry, physiological optics and systems genetics of refractive error have significantly advanced our understanding of the biological processes involved in refractive eye development and provided a framework for the development of new treatment options for myopia. In this review, we summarize the recent data on the mechanisms and signaling pathways underlying refractive eye development and discuss new evidence suggesting a wide-spread signal integration across different tissues and ocular components involved in visually guided eye growth.

Protective effects of sunlight exposure against PRK-induced myopia in infant rhesus monkeys.

PURPOSE: Extensive clinical evidence suggests that time spent outdoors might reduce the risk of myopia. This study aimed to determine whether increasing sunlight exposure has a protective effect on hyperopic-defocus induced myopia in a non-human primate. METHODS: Twelve 2-month-old rhesus monkeys were treated monocularly with photorefractive keratectomy (PRK) (4.0 D) and divided randomly into two groups: artificial light (AL; n = 6) and natural light (NL; n = 6). Monkeys in the AL group were reared under artificial (indoor) lighting (08:00-20:00 h). Monkeys in the NL group were exposed to natural (outdoor) lighting for 4 h (09:00-11:00 and 15:00-17:00 h). Ocular refraction, corneal power and axial dimensions were measured before sunlight exposure and every 10 days after PRK. At day 180, retinal histology and apoptosis activity were evaluated by hematoxylin and eosin (H&E) staining and terminal deoxynucleotidyl transferase biotin (dUTP) nick end labelling (TUNEL) assay. RESULTS: Mean (±SD) PRK induced anisometropia was +3.11 (0.33) D. At the end of the experiment, both eyes of the NL monkeys exhibited significantly more hyperopia and shorter vitreous chamber depths (VCD), compared with AL monkeys (p < 0.05). The NL group exhibited a significantly slower rate of compensation to the induced anisometropia than the AL group (p < 0.05). The retinas of both groups exhibited normal histology and levels of apoptosis. CONCLUSIONS: Moderate sunlight exposure exerts protective effects against the myopic shift resulting from PRK-induced defocus in monkeys. These results are consistent with current clinical findings that increased outdoor exposure protects against myopia development. Sunlight exposure should serve as an independent positive factor in human myopia control.

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.

Signals for defocus arise from longitudinal chromatic aberration in chick.

Chicks respond to two signals from longitudinal chromatic aberration (LCA): a wavelength defocus signal and a chromatic signal. Wavelength defocus predicts reduced axial eye growth in monochromatic short-wavelength light, compared to monochromatic long-wavelength light. Wavelength defocus may also influence growth in broadband light. In contrast, a chromatic signal predicts increased growth when short-wavelength contrast > long-wavelength contrast, but only when light is broadband. We aimed to investigate the influence of blue light, temporal frequency and contrast on these signals under broadband conditions. Starting at 12 to 13 days-old, 587 chicks were exposed to the experimental illumination conditions for three days for 8h/day and spent the remainder of their day in the dark. The stimuli were flickering lights, with a temporal frequency of 0.2 or 10 Hz, low (30%) or high contrast (80%), and a variety of ratios of cone contrast simulating the effects of defocus with LCA. There were two color conditions, with blue contrast (bPlus) and without (bMinus). Stimuli in the "bPlus" condition varied the amounts of long- (L), middle- (M_) and double (D-) cone contrast, relative to short- (S-) and (UV-) cone contrast, to simulate defocus. Stimuli in the "bMinus" condition only varied the relative modulations of the L + D vs. M cones. In all cases, the average of the stimuli was white, with an illuminance of 777 lux, with cone contrast created through temporal modulation. A Lenstar LS 900 and a Hartinger refractometer were used to measure ocular components and refraction. Wavelength defocus signals with relatively high S-cone contrast resulted in reduced axial growth, and more hyperopic refractions, under low-frequency conditions (p = 0.002), in response to the myopic defocus of blue light. Chromatic signals with relatively high S-cone contrast resulted in increased axial growth and more myopic refractions, under high frequency, low contrast, conditions (p < 0.001). We conclude that the chromatic signals from LCA are dependent on the temporal frequency, phase, and relative contrast of S-cone temporal modulation, and recommend broadband spectral and temporal environments, such as the outdoor environment, to optimize the signals-for-defocus in chick.

Establishment of correctly focused eyes may not require visual input in arthropods.

For proper function, vertebrate and invertebrate visual systems must be able to achieve and maintain emmetropia, a state where distant objects are in focus on the retina. In vertebrates, this is accomplished through a combination of genetic control during early development and homeostatic visual input that fine-tunes the optics of the eye. While emmetropization has long been researched in vertebrates, it is largely unknown how emmetropia is established in arthropods. We used a micro-ophthalmoscope to directly measure how the lens projects images onto the retina in the eyes of small, live arthropods, allowing us to compare the refractive states of light-reared and dark-reared arthropods. First, we measured the image-forming larval eyes of diving beetles (Thermonectus marmoratus), which are known to grow rapidly and dramatically between larval instars. Then, we measured the image-forming principal anterior-median eyes of jumping spiders (Phidippus audax) after emergence from their egg cases. Finally, we measured individual ommatidia in the compound eyes of flesh flies (Sarcophaga bullata) that had developed and emerged under either light or dark conditions. Surprisingly, and in sharp contrast to vertebrates, our data for this diverse set of arthropods suggest that visual input is inconsequential in regard to achieving well-focused eyes. Although it remains unclear whether visual input that is received after the initial development further improves focusing, these results suggest that at least the initial coordination between the lens refractive power and eye size in arthropods may be more strongly predetermined by developmental factors than is typically the case in vertebrates.

Monochromatic and white light and the regulation of eye growth.

Experiments employing monochromatic light have been used to investigate the role of longitudinal chromatic aberration (LCA) as possible signals for emmetropization for many years. LCA arising from the dispersion of light, causes differences in the focal length at different wavelengths and can impose defocus (wavelength defocus). Short-wavelength light focuses with a shorter focal length than long-wavelength light and, as such, would be expected to produce a smaller, more hyperopic eye. Emmetropization can respond to wavelength defocus since animals reared in monochromatic light adjust their refractive state relative to that measured in white light. In many species, animals reared in monochromatic light respond as predicted by wavelength defocus, becoming more hyperopic in blue light and more myopic in red light. However, tree shrews and rhesus monkey become more hyperopic in red light, and while tree shrews initially become more hyperopic in blue light, they later become more myopic. This review examines the experiments performed in monochromatic light and highlights the potential differences in protocols affecting the results, including experiment duration, circadian rhythm stimulation, light intensity, bandwidth, humoral factors and temporal sensitivity.

The effects of partial and full correction of refractive errors on sensorial and motor outcomes in children with refractive accommodative esotropia.

PURPOSE: To investigate the effects of partial and full correction of refractive errors on sensorial and motor outcomes in children with refractive accommodative esotropia (RAE). METHODS: The records of pediatric cases with full RAE were reviewed; their first and last sensorial and motor findings were evaluated in two groups, classified as partial (Group 1) and full correction (Group 2) of refractive errors. RESULTS: The mean age at first admission was 5.84 ± 3.62 years in Group 1 (n = 35) and 6.35 ± 3.26 years in Group 2 (n = 46) (p = 0.335). Mean change in best corrected visual acuity (BCVA) was 0.24 ± 0.17 logarithm of the minimum angle of resolution (logMAR) in Group 1 and 0.13 ± 0.16 logMAR in Group 2 (p = 0.001). Duration of deviation, baseline refraction and amount of reduced refraction showed significant effects on change in BCVA (p < 0.05). Significant correlation was determined between binocular vision (BOV), duration of deviation and uncorrected baseline amount of deviation (p < 0.05). The baseline BOV rates were significantly high in fully corrected Group 2, and also were found to have increased in Group 1 (p < 0.05). Change in refraction was - 0.09 ± 1.08 and + 0.35 ± 0.76 diopters in Groups 1 and 2, respectively (p = 0.005). Duration of deviation, baseline refraction and the amount of reduced refraction had significant effects on change in refraction (p < 0.05). Change in deviation without refractive correction was - 0.74 ± 7.22 prism diopters in Group 1 and - 3.24 ± 10.41 prism diopters in Group 2 (p = 0.472). Duration of follow-up and uncorrected baseline deviation showed significant effects on change in deviation (p < 0.05). CONCLUSIONS: Although the BOV rates and BCVA were initially high in fully corrected patients, they finally improved significantly in both the fully and partially corrected patients. Full hypermetropic correction may also cause an increase in the refractive error with a possible negative effect on emmetropization. The negative effect of the duration of deviation on BOV and BCVA demonstrates the significance of early treatment in RAE cases.