Form Deprivation Research Articles

Photopic visual input is necessary for emmetropization in mice

It was recently demonstrated that refractive errors in mice stabilize around emmetropic values during early postnatal development, and that they develop experimental myopia in response to both visual form deprivation and imposed optical defocus similar to other vertebrate species. Animal studies also suggest that photopic vision plays critical role in emmetropization in diurnal species; however, it is unknown whether refractive eye development is guided by photopic vision in the mouse, which is a nocturnal species. We used an infrared mouse photorefractor and a high-resolution MRI to clarify the role of photopic visual input in refractive eye development in the mouse. Refractive eye development and form-deprivation myopia in P21–P89 C57BL/6J mice were analyzed under 12:12 h light–dark cycle, constant light and constant darkness regimens. Animals in all experimental groups were myopic at P21 (−13.2 ± 1.6 D, light–dark cycle; −12.5 ± 0.9 D, constant light; −12.5 ± 2.0 D, constant dark). The mean refractive error in the light–dark-cycle-reared animals was −0.5 ± 1.3 D at P32 and, and did not change significantly until P40 (+0.3 ± 0.6 D, P40). Animals in this group became progressively hyperopic between P40 and P89 (+2.2 ± 0.6 D, P67; +3.7 ± 2.0 D, P89). The mean refractive error in the constant-light-reared mice was −1.0 ± 0.7 D at P32 and remained stable until P89 (+0.1 ± 0.6 D, P40; +0.3 ± 0.6 D, P67; 0.0 ± 0.4 D, P89). Dark-reared animals exhibited highly hyperopic refractive errors at P32 (+5.2 ± 1.8 D) and became progressively more hyperopic with age (+8.7 ± 1.9 D, P40; +11.2 ± 1.4 D, P67). MRI analysis revealed that emmetropization in the P40–P89 constant-light-reared animals was associated with larger eyes, a longer axial length and a larger vitreous chamber compared to the light–dark-cycle-reared mice. Constant-light-reared mice also developed 4 times higher degrees of form-deprivation myopia on average compared to light–dark-cycle-reared animals (−12.0 ± 1.4 D, constant light; −2.7 ± 0.7 D, light–dark cycle). Dark-rearing completely prevented the development of form-deprivation myopia (−0.3 ± 0.5 D). Thus, photopic vision plays important role in normal refractive eye development and ocular response to visual form deprivation in the mouse.

Expression of Perineuronal Nets, Parvalbumin and Protein Tyrosine Phosphatase σ in the Rat Visual Cortex During Development and After BFD

Purpose of the Study: Protein tyrosine phosphatase σ (PTPσ) acts as a neuronal receptor for chondroitin sulfate proteoglycans (CSPGs). CSPGs have inhibitory effects on experience-dependent plasticity and usually form lattice-like cell coatings that surround the parvalbumin (PV) interneurons in the visual cortex (VC). We investigated developmental changes and the effect of binocular form deprivation (BFD) on PTPσ, perineuronal nets (PNNs) and their tempo-spatial relationships with PV neurons in the VC.Materials and Methods: Double-immunostaining was used to observe the coexpression pattern of PNNs staining by biotinylated wisteria floribunda lectin (WFA) with PV neurons. The expression of PTPσ in the VC of Long Evans rats was detected by real-time quantitative PCR, immunohistochemistry and western blots. The changes in the number of PV/WFA/PTPσ labeled cells in layer IV of the VC and its proportion of PV neurons were examined during development and after BFD.Results: The expression of PV neurons wrapped by PNNs was increased, particularly in the first half of the critical period, and the ratio for PV neurons reached the highest level (over 75%) at adulthood, indicating that PNNs may play an important role in the maturation of PV neurons during the critical period. BFD decreased the density of PNNs and the percentage of PV neurons with PNNs. This result suggests that the number of PNNs surrounding PV neurons may be experience-dependent. Meanwhile, the CSPG receptor PTPσ was maintained at its lowest level during the critical period and could be modulated by BFD after the critical period. The percentage of PV/WFA/PTPσ-positive cells in PV population increased during development and reached its highest ratio at adulthood, which could also be reversed by BFD.Conclusions: The changes in the coexpression of PNNs, PV and PTPσ provide valuable insights into the connection between CSPGs and PV neurons.

Form deprivation and lens‐induced myopia: are they different?

In the following point-counterpoint article, internationally-acclaimed myopia researchers were challenged to defend the two opposing sides of the topic defined by the title; their contributions, which appear in the order Point followed by Counterpoint, were peer-reviewed by both the editorial team and an external reviewer. Independently of the invited authors, the named member of the editorial team provided an Introduction and Summary, both of which were reviewed by the other members of the editorial team. By their nature, views expressed in each section of the Point-Counterpoint article are those of the author concerned and may not reflect the views of all of the authors.

Effects of muscarinic agents on chick choroids in intact eyes and eyecups: evidence for a muscarinic mechanism in choroidal thinning

In chicks, ocular growth inhibition is associated with choroidal thickening and growth stimulation with choroidal thinning, suggesting a mechanistic link between the two responses. Because muscarinic antagonists inhibit the development of myopia in animal models by a non-accommodative mechanism, we tested the hypothesis that agonists would stimulate eye growth and thin the choroid. We also hypothesized that the effective growth-inhibiting antagonists would thicken the choroid. Chicks, age 12-16 days, were used. In vivo: Agonists: Single intravitreal injections (20 μL) of oxotremorine (oxo), pilocarpine (pilo), carbachol (carb), or arecaidine (arec) were given to otherwise untreated eyes. A-scan ultrasonography was done prior to injections, and at 3, 24, 48 and 72 h. Antagonists: -10D lenses were worn on one eye for 4 days. Atropine (atro), pirenzepine (pirz), oxyphenonium (oxy) or dicyclomine (dicy) were injected (20 μL) daily into lens-wearing eyes; saline injections were done as controls. Ultrasonography was done on d1 and on d4; on d4 measurements were done before and 3 h after injections. In vitro: Paired eyecups of retinal pigment epithelium (RPE), choroid and sclera were made from 1-week old chicks. All drugs except atropine were tested on one eyecup, its pair in plain medium. Choroidal thickness was measured at various times over 48 h. Agonists: In vivo, oxotremorine caused an increase in the rate of axial elongation (drug vs saline: 24-72 h: 338 μm vs 250 μm; p < 0.001). All except pilocarpine caused choroidal thinning by 24 h (oxo, carb and arec vs saline: -25, -35 and -46 μm vs 3 μm). In vitro, all agonists thinned choroids by 24 h (oxo: -6 vs 111 μm; pilo: 45 vs 212 μm; carb: -58 vs 65 μm; arec: 47 vs 139 μm; p < 0.05). Antagonists: Atropine, pirenzepine and oxyphenonium inhibited the development of myopia in negative lens-wearing eyes, and also caused choroidal thickening (drug vs saline: 42, 80, 88 vs 10 μm per 3 h). In vitro, pirenzepine thickened choroids by 3 h (77 vs 2 μm, p < 0.01). Muscarinic agonists caused choroidal thinning in intact eyes and eyecups, supporting a role for acetylcholine in the choroidal response to hyperopic defocus or form deprivation. Only oxotremorine stimulated eye growth, which is inconsistent with a muscarinic receptor mechanism for antagonist-induced eye growth inhibition. The dissociation between choroidal thinning and ocular growth stimulation for the other agonists in vivo suggest separate pathways for the two.

An introduction to Point‐Counterpoint articles

In a departure from its usual format of original articles, editorials and reviews, this Special Issue of OPO features a remarkable series of six ‘Point-Counterpoint’ articles, in which leading researchers were invited to debate critical issues in myopia research. With a tight word count and reference limit, the Point-Counterpoint format offers a way for authors to provide a concise summary of a topic while conveying the excitement and intrigue that surrounds it. We asked contributors to be as provocative and outspoken in their points and counterpoints as the research literature allowed, in order to fully expose questions and uncertainties that might otherwise be familiar only to specialists, or that might be tucked away deep in the Discussion sections of rare, dusty old manuscripts. The panel of selected experts has not let us down. The six topics under discussion range from fundamental, academic research questions through to translational issues of urgent clinical relevance. Myopia researchers have drawn heavily on studies in animal models over the years, generally employing two kinds of visual manipulations to induce myopia: form deprivation and imposed hyperopic defocus (negative lens wear). The extent to which these two experimental manipulations emulate the causal mechanisms in human myopia is a crucially important question, but one that is almost impossible to gauge at present. However, the closely related question of whether the two treatments invoke enhanced eye growth through a common mechanism has been amenable to experimental investigation. In the first Point-Counterpoint article, Ian Morgan and Regan Ashby argue the case for similarities in the mechanism(s) underlying form-deprivation myopia and lens-induced myopia, with Debora Nickla taking the opposing view that the mechanisms are different. In the second Point-Counterpoint article, Frank Schaeffel and Christine Wildsoet debate what is possibly the most intriguing question in myopia research today, ‘Can the retina alone detect the sign of defocus?’ (this topic is particularly apt for a Special Issue of OPO dedicated to Josh Wallman, as much of Josh's myopia research addressed this problem). Perceptually, blur caused by an image focused in front of, or behind, the retina is difficult to distinguish. Yet, many lines of evidence suggest the retina can accomplish the task, even when artificially ‘disconnected’ from higher brain centres. As myopic and hyperopic defocus drive eye growth in opposite directions, understanding the retina's abilities and limitations in interpreting blur thus offer an enticing route towards a myopia-prevention therapy. Clinical trials currently underway are examining whether increasing the time spent outdoors can slow myopia progression. However, in parts of the world where the prevalence of myopia is highest, parents are often reluctant to let their children play outside for long periods. The third Point-Counterpoint article discusses the timely question of whether high light intensity, typical of that outdoors, is protective against myopia, with Ian Flitcroft and the trio of Cheryl Ngo, Seang Mei Saw and Ramamurthy Dharani taking the opposing views. If a high light level per se is crucial, then would fitting classrooms with super-bright lighting be beneficial? Also pertinent to the theme of interventions to slow myopia progression, the fourth and fifth Point-Counterpoint articles see Neville McBrien, Brittany Carr and William Stell debate the mechanism by which atropine exerts its anti-myopia effect, and Earl Smith and the duo of Melanie Campbell and Elizabeth Irving debate whether peripheral retinal signalling underlies the anti-myopia effect of corneal reshaping therapy (CRT) and dual-focus contact lenses. There is renewed interest in the use of atropine as a treatment for myopia following promising results from clinical trials using very low dose therapy. As two of the drug's most important side-effects – mydriasis and cycloplegia – seem unrelated to atropine's anti-myopia modus operandi, and are dose-dependent, it might be possible to avoid them while preserving clinical efficacy. Clinical trials using CRT and multi-focal contact lenses have also yielded impressive outcomes in recent years. In the fifth Point-Counterpoint article, the debate surrounds the extent to which the peripheral retina can over-ride signals generated by the central retina, and indeed whether such peripheral retina-dominated effects can explain how CRT and dual-focus lenses slow myopia progression. Looking to the future, the last in this series of Point-Counterpoint articles sees Ahmed Elsheikh and John Philips explore the potential of scleral cross-linking as a therapy for myopia. Can we expect the success achieved in treating keratoconus to be mirrored in a treatment for myopia, or are the safety issues and surgical complexities too great to overcome? To quote Friedrich Nietzsche, ‘Those who cannot understand how to put their thoughts on ice should not enter into the heat of debate’. On that note, we hope you enjoy the steely cold, scientific arguments presented in this series!

The effects and interactions of GABAergic and dopaminergic agents in the prevention of form deprivation myopia by brief periods of normal vision

Intravitreal injections of GABA antagonists, dopamine agonists and brief periods of normal vision have been shown separately to inhibit form-deprivation myopia (FDM). Our study had three aims: (i) establish whether GABAergic agents modify the myopia protective effect of normal vision, (ii) investigate the receptor sub-type specificity of any observed effect, and (iii) consider an interaction with the dopamine (DA) system. Prior to the period of normal vision GABAergic agents were applied either (i) individually, (ii) in combination with other GABAergic agents (an agonist with an antagonist), or (iii) in combination with DA agonists and antagonists. Water injections were given to groups not receiving drug treatments so that all experimental eyes received intravitreal injections. As shown previously, constant form-deprivation resulted in high myopia and when diffusers were removed for 2 h per day the period of normal vision greatly reduced the FDM that developed. GABA agonists inhibited the protective effect of normal vision whereas antagonists had the opposite effect. GABAA/C agonists and D2 DA antagonists when used in combination were additive in suppressing the protective effect of normal vision. A D2 DA agonist restored some of the protective effect of normal vision that was inhibited by a GABA agonist (muscimol). The protective effect of normal vision against form-deprivation is modifiable by both the GABAergic and DAergic pathways.

Is myopia a failure of homeostasis?

This review examines the hypothesis that human myopia is primarily a failure of homeostasis (i.e. regulated growth) and also considers the implications this has for research into refractive errors. There is ample evidence for homeostatic mechanisms in early life. During the first few years of life the eye grows toward emmetropia, a process called emmetropization. The key statistical features of this process are a shift of the mean population refraction toward emmetropia and a reduction in variability. Refractive errors result when either this process fails (primary homeostatic failure) or when an eye that becomes emmetropic fails to remain so during subsequent years (secondary homeostatic failure). A failure of homeostasis should increase variability as well as causing a possible shift in mean refraction. Increased variability is indeed seen in both animal models of myopia such as form deprivation and in human populations from the age of 5 or 6 onwards. Considering ametropia as a homeostatic failure also fits with the growing body of evidence that a wide range of factors and events can influence eye growth and refraction from gestation, through infancy, childhood and into adulthood. It is very important to recognize that the refraction of an eye is not a simple trait like eye colour but the consequence of the complex process of eye growth throughout life. To understand how an eye ends up with a specific refraction it is essential to understand all the factors that may promote the attainment and maintenance of emmetropia. Equally important are the factors that may either disrupt early emmetropization or lead to a loss of emmetropia during later development. Therefore, perhaps the most important single implication of a homeostatic view of myopia is that this condition is likely to have a very wide range of causes. This may allow us to identify subgroups of myopia for which specific environmental influences, genes or treatments can be found, effects that might be lost if all myopes are considered to be equivalent.

Mechanism of the DL-alpha-aminoadipic acid inhibitory effect on form-deprived myopia in guinea pig.

To investigate the effect of intravitreal injection of DL-alpha-aminoadipic acid (DL-α-AAA) on ocular refractive state and retinal dopamine, transforming growth factor-β2 (TGFβ2), vasoactive intestinal polypeptide (VIP) in guinea pig form-deprived myopia. Four-week-old pigmented guinea pigs were randomly assigned to 4 groups: normal control, deprivation, deprivation plus DL-α-AAA, deprivation plus saline. Form deprivation was induced with the self-made translucent eye shields, and lasted for 14 days. 8µg DL-α-AAA was injected into the vitreous chamber of deprived eyes. The corneal radius of curvature, refraction and axial length were measured. Retinal dopamine content was evaluated by the high-performance liquid chromatography with electrochemical detection, and TGFβ2 and VIP protein were detected by Western blotting. Fourteen days of eye occlusion caused the axial length to elongate and become myopic in the form-deprived eyes, with the decrease of retinal dopamine and the increase of TGFβ2 and vasoactive intestinal polypeptide (VIP) protein. Intravitreal injection of DL-α-AAA could inhibit the myopic shift from (-3.65±1.06)D to (-1.48±0.63)D, P<0.01 due to goggles occluding and cause the decrease of retinal TGFβ2 protein in the deprived eyes. However, intravitreal injection of DL-α-AAA had no significant effect on retinal dopamine and VIP protein in deprived eyes. Retinal TGFβ2 protein correlated highly with the ocular refraction (y=-3.34+0.31/x, F=74.75, P<0.001) and axial length (y=8.39-0.02/x, F=48.32, P<0.001) in different treatment groups. Intravitreal injection of DL-α-AAA is effectively able to suppress the development of form deprivation myopia, which may be associated with retinal TGFβ2 protein in guinea pigs.

Community-based rehabilitation in Jordan: challenges to achieving occupational justice

Purpose: This paper presents theories of occupational and social justice and applies the theoretical tenets to a community-based rehabilitation (CBR) program in a Palestinian refugee camp in Jordan. Method: The example of building a playground for children with disabilities, and other aspects of the social, political and cultural context in Jordan are described in relation to the theory and practice of CBR, occupational and social justice. Results: Key concepts are explained, analyzed and applied, namely occupational justice, social justice, occupational form and occupational deprivation (a strong determinant of occupational injustice), all of which were relevant in the refugee camp where children with disabilities were deprived of resources and chances to play. Conclusion: Grounding CBR in an occupational justice framework offers justification and inspiration for occupational therapy in similar settings deprived of resources and opportunities wherein both individuals and communities could benefit.Implications for RehabilitationOccupational deprivation, such as that seen in refugee camps, is associated with poor mental health and physical frailty.CBR in refugee camps can lead to both occupational justice and social justice for persons with disabilities.Disability laws and legislation must be implemented, not just stated on paper, in order to address the rights of persons with disabilities and social justice.

Ocular diurnal rhythms and eye growth regulation: Where we are 50 years after Lauber

Many ocular processes show diurnal oscillations that optimize retinal function under the different conditions of ambient illumination encountered over the course of the 24 h light/dark cycle. Abolishing the diurnal cues by the use of constant darkness or constant light results in excessive ocular elongation, corneal flattening, and attendant refractive errors. A prevailing hypothesis is that the absence of the Zeitgeber of light and dark alters ocular circadian rhythms in some manner, and results in an inability of the eye to regulate its growth in order to achieve emmetropia, the matching of the front optics to eye length. Another visual manipulation that results in the eye growth system going into a “default” mode of excessive growth is form deprivation, in which a translucent diffuser deprives the eye of visual transients (spatial or temporal) while not significantly reducing light levels; these eyes rapidly elongate and become myopic. It has been hypothesized that form deprivation might constitute a type of “constant condition” whereby the absence of visual transients drives the eye into a similar default mode as that in response to constant light or dark. Interest in the potential influence of light cycles and ambient lighting in human myopia development has been spurred by a recent study showing a positive association between the amount of time that children spent outdoors and a reduced prevalence of myopia. The growing eyes of chickens and monkeys show a diurnal rhythm in axial length: Eyes elongate more during the day than during the night. There is also a rhythm in choroidal thickness that is in approximate anti-phase to the rhythm in eye length. The phases are altered in eyes growing too fast, in response to form deprivation or negative lenses, or too slowly, in response to myopic defocus, suggesting an influence of phase on the emmetropization system. Other potential rhythmic influences include dopamine and melatonin, which form a reciprocal feedback loop, and signal “day” and “night” respectively. Retinal dopamine is reduced during the day in form deprived myopic eyes, and dopamine D2 agonists inhibit ocular growth in animal models. Rhythms in intraocular pressure as well, may influence eye growth, perhaps as a mechanical stimulus triggering changes in scleral extracellular matrix synthesis. Finally, evidence shows varying influences of environmental lighting parameters on the emmetropization system, such as high intensity light being protective against myopia in chickens. This review will cover the evidence for the possible influence of these various factors on ocular growth. The recognition that ocular rhythms may play a role in emmetropization is a first step toward understanding how they may be manipulated in treatment therapies to prevent myopia in humans.

Optical treatment strategies to slow myopia progression: Effects of the visual extent of the optical treatment zone

In order to develop effective optical treatment strategies for myopia, it is important to understand how visual experience influences refractive development. Beginning with the discovery of the phenomenon of form deprivation myopia, research involving many animal species has demonstrated that refractive development is regulated by visual feedback. In particular, animal studies have shown that optically imposed myopic defocus slows axial elongation, that the effects of vision are dominated by local retinal mechanisms, and that peripheral vision can dominate central refractive development. In this review, the results obtained from clinical trials of traditional optical treatment strategies employed in efforts to slow myopia progression in children are interpreted in light of the results from animal studies and are compared to the emerging results from preliminary clinical studies of optical treatment strategies that manipulate the effective focus of the peripheral retina. Overall, the results suggest that imposed myopic defocus can slow myopia progression in children and that the effectiveness of an optical treatment strategy in reducing myopia progression is influenced by the extent of the visual field that is manipulated.

The Measurement and Treatment of Suppression in Amblyopia

Amblyopia, a developmental disorder of the visual cortex, is one of the leading causes of visual dysfunction in the working age population. Current estimates put the prevalence of amblyopia at approximately 1-3%1-3, the majority of cases being monocular2. Amblyopia is most frequently caused by ocular misalignment (strabismus), blur induced by unequal refractive error (anisometropia), and in some cases by form deprivation. Although amblyopia is initially caused by abnormal visual input in infancy, once established, the visual deficit often remains when normal visual input has been restored using surgery and/or refractive correction. This is because amblyopia is the result of abnormal visual cortex development rather than a problem with the amblyopic eye itself4,5 . Amblyopia is characterized by both monocular and binocular deficits6,7 which include impaired visual acuity and poor or absent stereopsis respectively. The visual dysfunction in amblyopia is often associated with a strong suppression of the inputs from the amblyopic eye under binocular viewing conditions8. Recent work has indicated that suppression may play a central role in both the monocular and binocular deficits associated with amblyopia9,10 . Current clinical tests for suppression tend to verify the presence or absence of suppression rather than giving a quantitative measurement of the degree of suppression. Here we describe a technique for measuring amblyopic suppression with a compact, portable device11,12 . The device consists of a laptop computer connected to a pair of virtual reality goggles. The novelty of the technique lies in the way we present visual stimuli to measure suppression. Stimuli are shown to the amblyopic eye at high contrast while the contrast of the stimuli shown to the non-amblyopic eye are varied. Patients perform a simple signal/noise task that allows for a precise measurement of the strength of excitatory binocular interactions. The contrast offset at which neither eye has a performance advantage is a measure of the "balance point" and is a direct measure of suppression. This technique has been validated psychophysically both in control13,14 and patient6,9,11 populations. In addition to measuring suppression this technique also forms the basis of a novel form of treatment to decrease suppression over time and improve binocular and often monocular function in adult patients with amblyopia12,15,16 . This new treatment approach can be deployed either on the goggle system described above or on a specially modified iPod touch device15.

The Measurement and Treatment of Suppression in Amblyopia

Amblyopia, a developmental disorder of the visual cortex, is one of the leading causes of visual dysfunction in the working age population. Current estimates put the prevalence of amblyopia at approximately 1-3%1-3, the majority of cases being monocular2. Amblyopia is most frequently caused by ocular misalignment (strabismus), blur induced by unequal refractive error (anisometropia), and in some cases by form deprivation.Although amblyopia is initially caused by abnormal visual input in infancy, once established, the visual deficit often remains when normal visual input has been restored using surgery and/or refractive correction. This is because amblyopia is the result of abnormal visual cortex development rather than a problem with the amblyopic eye itself4,5 . Amblyopia is characterized by both monocular and binocular deficits6,7 which include impaired visual acuity and poor or absent stereopsis respectively. The visual dysfunction in amblyopia is often associated with a strong suppression of the inputs from the amblyopic eye under binocular viewing conditions8. Recent work has indicated that suppression may play a central role in both the monocular and binocular deficits associated with amblyopia9,10 .Current clinical tests for suppression tend to verify the presence or absence of suppression rather than giving a quantitative measurement of the degree of suppression. Here we describe a technique for measuring amblyopic suppression with a compact, portable device11,12 . The device consists of a laptop computer connected to a pair of virtual reality goggles. The novelty of the technique lies in the way we present visual stimuli to measure suppression. Stimuli are shown to the amblyopic eye at high contrast while the contrast of the stimuli shown to the non-amblyopic eye are varied. Patients perform a simple signal/noise task that allows for a precise measurement of the strength of excitatory binocular interactions. The contrast offset at which neither eye has a performance advantage is a measure of the "balance point" and is a direct measure of suppression. This technique has been validated psychophysically both in control13,14 and patient6,9,11 populations.In addition to measuring suppression this technique also forms the basis of a novel form of treatment to decrease suppression over time and improve binocular and often monocular function in adult patients with amblyopia12,15,16 . This new treatment approach can be deployed either on the goggle system described above or on a specially modified iPod touch device15.

The expression of c-fos gene in retina of flickering light-induced and form deprivation myopia

Background Flickering light is different from the normal light environment.Animal experiment proved that flickering light can induce myopia.But its mechanism remains unclear.Objective This study was to investigate the expression of c-fos gene in retina of myopic C57BL/6J mice induced by flickering light and monocular form deprivation.Methods Ninety clean C57BL/6J mice aged 28-day-old with the similar refraction in both eyes were randomly assigned to five groups.Fifteen mice in the control group were exposed to continuous white light environment.The white flickering light with the frequency of 10,5,2 Hz were used to irradiate the mice respectively in high frequency flickering group (15 mice),moderate frequency flickering group (15 mice) and low frequency flickering group (15 mice),respectively.The right eyes of other 30 mice were monocularly occluded with a semitransparent hemispherical thin plastic shell to establish the form deprivation models and then were exposed to white light environment.The diopter and ocular axial length were measured by murine-specific eccentric infrared photorefraction and A-scan ultrasonography before experiment and two weeks after the treatments.At the end of experiment,the mice were sacrificed by neck dislocation.Mice eyes were enucleated and retinal samples were prepared for the detect of c-fos protein and its mRNA by immunohistochemistry,Western blot and reverse transcription polymerase chain reaction (RT-PCR),respectively.Results Immunohistochemistry showed that the expressing rate ofc-fos protein in retina was (68.000±10.368)％,(51.000±6.519)％,(46.000±6.519)％,(31.000±7.416)％ and (25.000 ± 7.071)％ in the control group,high frequency flickering group,moderate frequency flickering group,low frequency flickering group and form deprivation group respectively 2 weeks after experiment.The expression rates of c-fos protein in retina in different frequencies of flickering light groups and form deprivation group were significantly lower than that in the control group (t =3.104,4.017,6.490,7.661,all P＜0.05),with the lowest rate in the form deprivation group (P＜0.05).The expression of c-fos detected by Western blot assay exhibited that the relative values of c-fos protein in retina (c-fos/GAPDH) was 0.804±0.050,0.687±0.047,0.667±0.036,0.558±0.036 and 0.532 ±0.056,respectively in the control group,high frequency flickering group,moderate frequency flickering group,low frequency flickering group and form deprivation group,illustrating significantly lowing in different frequencies of flickering light groups and form deprivation group compared with control group (t =2.961,3.184,6.971,6.276,all P＜0.05),whereas the c-fos in the low frequency group and form deprivation group,c-fos protein was less expressed in comparison with the higher frequency flicking group (P＜0.05).The expression level of c-fos mRNA (c-fos mRNA/GAPDH mRNA) in retina was 0.820±0.056,0.663±0.061,0.627±0.034,0.521±0.041 and 0.474 ±0.045 in the control group,high frequency flickering group,moderate frequency flickering group,low frequency flickering group and form deprivation group,respectively.These results demonstrated a significant decline in the expression of c-fos mRNA in different frequencies of flickering group and form deprivation group compared with the control group(t=3.262,5.070,7.173,8.305,all P＜0.05),and the inhibition ability of low frequency of flickering group and form deprivation group was much stronger.Conclusions The c-fos gene level in the retina has a negative relationship with the severity of myopia induced by flickering light and form deprivation. Key words: c-fos gene; Refractive error/myopia; Flickering light; Form deprivation

Binocular form deprivation influences the visual cortex.

α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors are considered to play a crucial role in synaptic plasticity in the developing visual cortex. In this study, we established a rat model of binocular form deprivation by suturing the rat binocular eyelids before eye-opening at postnatal day 14. During development, the decay time of excitatory postsynaptic currents mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors of normal rats became longer after eye-opening; however, the decay time did not change significantly in binocular form deprivation rats. The peak value in the normal group became gradually larger with age, but there was no significant change in the binocular form deprivation group. These findings indicate that binocular form deprivation influences the properties of excitatory postsynaptic currents mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors in the rat visual cortex around the end of the critical period, indicating that form stimulation is associated with the experience-dependent modification of neuronal synapses in the visual cortex.

Recovery of peripheral refractive errors and ocular shape in rhesus monkeys (Macaca mulatta) with experimentally induced myopia

This study aimed to investigate the changes in ocular shape and relative peripheral refraction during the recovery from myopia produced by form deprivation (FD) and hyperopic defocus. FD was imposed in six monkeys by securing a diffuser lens over one eye; hyperopic defocus was produced in another six monkeys by fitting one eye with −3D spectacle. When unrestricted vision was re-established, the treated eyes recovered from the vision-induced central and peripheral refractive errors. The recovery of peripheral refractive errors was associated with corresponding changes in the shape of the posterior globe. The results suggest that vision can actively regulate ocular shape and the development of central and peripheral refractions in infant primates.

Ambient illuminance, retinal dopamine release and refractive development in chicks

Form deprivation and low illuminance of ambient light are known to induce myopia in chicks. Low concentrations of retinal dopamine, a light-driven neurohormone, was previously shown to be associated with form deprivation myopia. In the present study we examined the dependence of retinal dopamine release in chicks on illuminance during light–dark cycles and in continuous light, and the role of retinal dopamine release in illuminance dependent refractive development. Newly hatched chicks (n = 166) were divided into two experimental groups, a dopamine (n = 88) and a refraction group (n = 78). Both groups were further divided into six illumination groups for exposure of chicks to illuminances of 50, 500 or 10,000 lux of incandescent illumination (referred to throughout as low, medium, and high illuminance, respectively), either under a light–dark cycle with lights on between 7 AM and 7 PM or under continuous illumination. For the dopamine experiment, chicks were euthanized and vitreous was extracted on day 14 post-hatching at 7, 8 AM and 1 PM. Vitreal dihydroxyphenylacetic acid (DOPAC) and dopamine concentrations were quantified by high-performance liquid chromatography coupled to electrochemical detection. For the refraction experiment, chicks underwent refraction, keratometry and A-scan ultrasonography on days 30, 60 and 90 post-hatching, and each of those measurements was correlated with vitreal DOPAC concentration measured at 1 PM (representing the index of retinal dopamine release). The results showed that under light–dark cycles, vitreal DOPAC concentration was strongly correlated with log illuminance, and was significantly correlated with the developing refraction, corneal radius of curvature, and axial length values. On day 90, low vitreal DOPAC concentrations were associated with myopia (−2.41 ± 1.23 D), flat cornea, deep anterior and vitreous chambers, and thin lens. Under continuous light, vitreal DOPAC concentrations measured at 1 PM in the low, medium, and high illuminance groups did not differ from the concentrations measured at 8 AM. On day 90, low DOPAC concentrations were associated with emmetropia (+0.63 ± 3.61), steep cornea, and shallow vitreous chamber. We concluded that ambient light over a log illuminance range of 1.69–4 is linearly related to vitreal DOPAC concentration. Under both light–dark cycles and continuous light, the intensity of ambient light regulates the release of retinal dopamine. Refractive development is associated with illuminance dependent dopamine release.

Vision-guided ocular growth in a mutant chicken model with diminished visual acuity

Visual experience is known to guide ocular growth. We tested the hypothesis that vision-guided ocular growth is disrupted in a model system with diminished visual acuity. We examine whether ocular elongation is influenced by form-deprivation (FD) and lens-imposed defocus in the Retinopathy, Globe Enlarged (RGE) chicken. Young RGE chicks have poor visual acuity, without significant retinal pathology, resulting from a mutation in guanine nucleotide-binding protein β3 (GNB3), also known as transducin β3 or Gβ3. The mutation in GNB3 destabilizes the protein and causes a loss of Gβ3 from photoreceptors and ON-bipolar cells (Ritchey et al., 2010). FD increased ocular elongation in RGE eyes in a manner similar to that seen in wild-type (WT) eyes. By comparison, the excessive ocular elongation that results from hyperopic defocus was increased, whereas myopic defocus failed to significantly decrease ocular elongation in RGE eyes. Brief daily periods of unrestricted vision interrupting FD prevented ocular elongation in RGE chicks in a manner similar to that seen in WT chicks. Glucagonergic amacrine cells differentially expressed the immediate early gene Egr1 in response to growth-guiding stimuli in RGE retinas, but the defocus-dependent up-regulation of Egr1 was lesser in RGE retinas compared to that of WT retinas. We conclude that high visual acuity, and the retinal signaling mediated by Gβ3, is not required for emmetropization and the excessive ocular elongation caused by FD and hyperopic defocus. However, the loss of acuity and Gβ3 from RGE retinas causes enhanced responses to hyperopic defocus and diminished responses to myopic defocus.

Parasympathetic influences on emmetropization in chicks: Evidence for different mechanisms in form deprivation vs negative lens-induced myopia

Ciliary ganglionectomy inhibits the development of myopia in chicks (Schmid et al., 1999), but has no effect on the compensatory responses to spectacle lenses (Schmid and Wildsoet, 1996). This study was done to assess the potential influence of the other parasympathetic input to the choroid, the pterygopalatine ganglia, on the choroidal and axial responses to retinal defocus, and to form deprivation.4–5 week-old chicks had one of the following surgeries to one eye: (1) Section (X) of the autonomic part of cranial N VII (input to the pterygopalatine ganglia) (PPGX, n = 16), (2) PPGX plus ciliary ganglionectomy (PPG/CGX, n = 23) or (3) PPGX plus superior cervical ganglionectomy (PPG/SCGX, n = 10). Experimental eyes were fitted with positive or negative lenses, or diffusers, several days after surgery. In one group of PPG/CGX, eyes did not wear any devices (n = 8). Intact (no surgery) controls were done for all visual manipulations (lenses or diffusers). Sham surgeries were done for the PPG/CGX condition (n = 4). Ocular dimensions were measured using A-scan ultrasonography prior to the surgery, 5 days later when visual devices were placed on the eyes, at the end of lens- or diffuser-wear, and in the case of diffusers, 4 days after diffuser removal to look at “recovery”. Refractive errors were measured using a Hartinger's refractometer. IOP was measured in 7 PPG/CGX birds 7d after surgery.PPGX/CGX resulted in choroidal thickening (125 μm) and a decrease in IOP over one week post-surgery. It also prevented the development of myopia in response to form deprivation (X vs intact: 0.2 D vs −4.1 D; p < 0.005), by preventing the increase in axial elongation (250 μm vs 670 μm/5d; p < 0.005). In fact, growth rate slowed below normal (X vs fellow eyes: 250 μm vs 489 μm/5d; p = 0.002). By contrast, there were no effects of this lesion on the development of myopia in response to negative lenses (X vs intact: −5.4 D vs −5.3 D). All three lesions inhibited the compensatory choroidal thickening in response to myopic defocus (ANOVA, p = 0.0008), but had no effect on the thinning response to hyperopic defocus. These results argue for different underlying mechanisms for the growth responses to form deprivation vs negative lens wear. They also imply that choroidal thickening and thinning are not opposing elements of a single mechanism.

Flicker downregulates the content of crystallin proteins in form-deprived C57BL/6 mouse retina

Image degradation by loss of higher spatial frequencies causes form-deprivation myopia (FDM) in humans and animals, and cyclical illumination (flicker) at certain frequencies may prevent FDM. The molecular mechanisms underlying FDM and its prevention by flicker are poorly known. To understand them better, we have identified proteins that differ in amount in form-deprived (FD) mouse retinas, under steady versus flickering light. Male C57BL/6 mice (age 27–29 days) were randomly divided into three groups: Experimental – monocularly form-deprived, and kept under either normal room light (“FD-Only”) or 20 Hz flickering light (“FD-Flicker”), throughout the 12-hour light phase; and Control (“Open-Control”) – kept under normal illumination, without form deprivation. After two weeks of treatment, retinal proteins were extracted and separated by two-dimensional gel electrophoresis (2D-GE); proteins that differ in content in FD-only versus FD-flicker retinas were identified by mass spectroscopy (“MS”), and their identities were verified by western blotting. The contents of three identified proteins differed statistically in FD-only compared to FD-flicker retinas. These proteins were identified by MS as α-A-crystallin, crystallin β A2 and crystallin β A1. Quantitative western blotting showed that the relative amount of α-A-crystallin in FD-only retinas was significantly higher than that in FD-Flicker and control retinas. In conclusion, form deprivation induced significant increases in the amounts of crystallins in mouse retinas. These increases were significantly reduced by exposure to 20 Hz flicker. Since form deprivation is known to induce myopia development, and flicker to prevent it, our data suggest that FD- and flicker-responsive changes in the content of crystallin proteins may be involved causally or protectively in myopia development.