Dopamine synthesis and metabolism in rhesus monkey retina: development, aging, and the effects of monocular visual deprivation

Topical Dopamine Application on Form-Deprivation Myopia in Rabbits

Background/Objectives: This study aimed to investigate the efficacy of topical dopamine administration in inhibiting form deprivation (FD) myopia in a rabbit model. Methods: A total of 16 neonatal New Zealand white rabbits were randomly assigned to two groups: a control group and a dopamine treatment group. FD myopia was induced in both groups by applying a light diffuser to one eye. The dopamine group received daily topical instillations of 4% dopamine in the eye with FD myopia, while the control group received normal saline instillations over a four-week period. Axial length measurements were taken to assess the degree of myopia, and histological analysis was performed to evaluate retinal safety and structural integrity. Results: The results indicated that dopamine treatment significantly inhibited axial elongation of the FD eyes compared to the control group, with measurements of 15.07 ± 0.34 mm for the dopamine group versus 15.63 ± 0.33 mm for the control group (p = 0.015). Histological analysis showed no evidence of structural alterations or apoptosis in the retina, confirming the safety of topical dopamine. Conclusions: Topical dopamine appears to be a promising therapeutic approach for controlling the progression of myopia in a rabbit model, demonstrating significant efficacy in reducing axial elongation without inducing ocular toxicity. These findings highlight the potential of dopamine in managing myopia and warrant further investigation in clinical settings.

Modulation of All-Trans Retinoic Acid by Light and Dopamine in the Murine Eye

Purpose

Ambient light exposure is linked to myopia development in children and affects myopia susceptibility in animal models. Currently, it is unclear which signals mediate the effects of light on myopia. All-trans retinoic acid (atRA) and dopamine (DA) oppositely influence experimental myopia and may be involved in the retinoscleral signaling cascade underlying myopic eye growth. However, how ocular atRA responds to different lighting and whether atRA and DA interact remains unknown.

Methods

Dark-adapted C57BL/6J mice (29-31 days old) were exposed to dim (1 lux), mid (59 lux), or bright (12,000 lux) ambient lighting for 5 to 60 minutes. Some mice were also systemically administered the DA precursor, LDOPA, or atRA before light exposure. After exposure, the retina and the back of the eye (BOE) were collected and analyzed for levels of atRA, DA, and the DA metabolite, DOPAC.

Results

DA turnover (DOPAC/DA ratio) in the retina increased in magnitude after only 5 minutes of exposure to higher ambient luminance, but was minimal in the BOE. In contrast, atRA levels in the retina and BOE significantly decreased with higher ambient luminance and longer duration exposure. Intriguingly, LDOPA-treated mice had a transient reduction in retinal atRA compared with saline-treated mice, whereas atRA treatment had no effect on ocular DA.

Conclusions

Ocular atRA was affected by the duration of exposure to different ambient lighting, and retinal atRA levels decreased with increased DA. Overall, these data suggest specific interactions between ambient lighting, atRA, and DA that could have implications for the retinoscleral signaling cascade underlying myopic eye growth.

Refractive Development and Choroidal Vascularity in the Form-Deprivation Pigmented Rabbit Model

Purpose

This study assessed the characteristics of refractive development and choroidal vasculature in the form-deprivation (FD) pigmented rabbit model.

Methods

Monocular FD was performed in three-week-old pigmented rabbits (n = 18 for FD, n = 12 for control). Throughout the eight-week rearing period, refractive errors, corneal curvature radius (CCR), ocular biometric parameters, retinal thickness (RT), and choroidal thickness (ChT) were measured every two weeks using cycloplegic retinoscopy, keratometer, A-scan ultrasonography, and optical coherence tomography (OCT). The choroidal vascularity index (CVI) was calculated from OCT images by measuring the total choroidal area (TCA), stromal area (SA), and luminal area (LA). At the end of the form deprivation, the vitreous dopamine level was measured using an enzyme-linked immunosorbent assay kit.

Results

Relatively myopic refraction was induced in FD eyes after two, four, six, and eight weeks (interocular differences: -1.48 ± 0.88, -1.92 ± 0.90, -1.95 ± 0.80, and -2.00 ± 0.83 diopter; P < 0.001). Furthermore, FD eyes showed significantly longer axial length (AL) and vitreous chamber depth after eight weeks, with mean differences of 0.32 ± 0.03 and 0.32 ± 0.05 mm, respectively (P < 0.001). There were no significant differences in anterior chamber depth, lens thickness, CCR, and RT among the three groups through the intervention (all P > 0.05). After eight weeks, the average ChT of FD eyes was thinner than contralateral eyes (-19.37 ± 7.01 µm; P < 0.001). Additionally, the TCA, SA, and LA in FD eyes were smaller after four, six, and eight weeks (all P < 0.05, week 8: 0.3697 ± 0.0639 vs. 0.4272 ± 0.0968, 0.1047 ± 0.0221 vs. 0.1233 ± 0.0328, and 0.2650 ± 0.0459 vs. 0.3039 ± 0.0659 mm2, respectively). However, the CVI showed no significant difference among the three groups (P > 0.05). Finally, the concentration of vitreous dopamine was lower in the FD eyes, compared with contralateral and control eyes: 0.18 ± 0.20, 0.40 ± 0.67, and 0.33 ± 0.06 ng/mL, respectively (P < 0.05).

Conclusions

Form deprivation led to a relatively myopic shift in pigmented rabbits and a decrease in vitreous dopamine levels. In addition, with the lengthening of AL, the choroid thinned, but CVI remained unchanged.

Translational Relevance

Our study offered data about the refractive characteristics of pigmented rabbits to investigate myopia mechanisms. The modified method imaged the choroid of the inferior species more clearly, achieving in exploring the changes of choroidal vasculature in vivo.

Modulation of all- trans retinoic acid by light and dopamine in the murine eye

Purpose

Ambient light exposure is linked to myopia development in children and affects myopia susceptibility in animal models. Currently, it is unclear which signals mediate the effects of light on myopia. All- trans retinoic acid (atRA) and dopamine (DA) oppositely influence experimental myopia and may be involved in the retino-scleral signaling cascade underlying myopic eye growth. However, how ocular atRA responds to different lighting and whether atRA and DA interact remains unknown.

Methods

Dark-adapted C57BL/6J mice (29-31 days old) were exposed to Dim (1 lux), Mid (59 lux), or Bright (12,000 lux) ambient lighting for 5-60 minutes. Some mice were also systemically administered the DA precursor, LDOPA, or atRA prior to light exposure. After exposure, the retina and the back-of-the-eye (BOE) were collected and analyzed for levels of atRA, DA, and the DA metabolite, DOPAC.

Results

DA turnover (DOPAC/DA ratio) in the retina increased in magnitude after only five minutes of exposure to higher ambient luminance but was minimal in the BOE. In contrast, atRA levels in the retina and BOE significantly decreased with higher ambient luminance and longer duration exposure. Intriguingly, LDOPA-treated mice had a transient reduction in retinal atRA compared to saline-treated mice, whereas atRA treatment had no effect on ocular DA.

Conclusions

Ocular atRA was affected by the duration of exposure to different ambient lighting and retinal atRA levels decreased with increased DA. Overall, these data suggest specific interactions between ambient lighting, atRA, and DA that could have implications for the retino-scleral signaling cascade underlying myopic eye growth.

Loss of ON-Pathway Function in Mice Lacking Lrit3 Decreases Recovery From Lens-Induced Myopia

Purpose

To determine whether the Lrit3-/- mouse model of complete congenital stationary night blindness with an ON-pathway defect harbors myopic features and whether the genetic defect influences the recovery from lens-induced myopia.

Methods

Retinal levels of dopamine (DA) and 3,4 dihydroxyphenylacetic acid (DOPAC) from adult isolated Lrit3-/- retinas were quantified using ultra performance liquid chromatography after light adaptation. Natural refractive development of Lrit3-/- mice was measured from three weeks to nine weeks of age using an infrared photorefractometer. Susceptibility to myopia induction was assessed using a lens-induced myopia protocol with -25 D lenses placed in front of the right eye of the animals for three weeks; the mean interocular shift was measured with an infrared photorefractometer after two and three weeks of goggling and after one and two weeks after removal of goggles.

Results

Compared to wild-type littermates (Lrit3+/+), both DA and DOPAC were drastically reduced in Lrit3-/- retinas. Natural refractive development was normal but Lrit3-/- mice showed a higher myopic shift and a lower ability to recover from induced myopia.

Conclusions

Our data consolidate the link between ON pathway defect altered dopaminergic signaling and myopia. We document for the first time the role of ON pathway on the recovery from myopia induction.

Childhood amblyopia: A systematic review of recent management options

This study reviews the current information on treatment of childhood amblyopia, with the goal of improving visual functions. The authors searched various online databases including PubMed, Web of Science, ProQuest, Scopus, Google Scholar, Ebsco, and Medline. The articles, published between 2002 and 2023, included in this study were used to assess the different modalities for the management of different types of childhood amblyopia. The final systematic review included 41 studies from different countries, covering 4060 children with a mean age 6.8 ± 124 years. The findings showed that childhood amblyopia commonly treated through a systemic approach, i.e., starting with treatment of refractive errors with given optical adaptation time, followed by visually stimulating amblyopic eye by covering the dominant eye with patching, Atropine or Bangerter filters. Refractive adaptation period of 18-22 weeks has proven to show a significant improvement in visual acuity. It has been confirmed that 2 h patching is effective for the first time treated amblyopes, and if there is no improvement, increase the period to 6 h daily. Novel methods that improve binocular function such as dichoptic, perceptual training, video gaming, and drugs that facilitate visual neuroplasticity, are useful in the treatment of amblyopia that is not responsive to conventional therapy. The study concludes that significant evidence show that childhood amblyopia is treated through a systemic approach. Starting from correcting refractive errors with a period of optical adaptation, followed by patching therapy and atropine penalization. New methods that improve the binocular functions and medications that facilitate visual neuroplasticity have found to be useful in the treatment of amblyopia that is not responsive to conventional treatment.

The knowledge structure and research trends between light and myopia: A bibliometric analysis from 1981 to 2024

BACKGROUND

This bibliometric analysis explored the knowledge structure of and research trends in the relationship between light and myopia.

METHODS

Relevant literature published from 1981 to 2024 was collected from the Web of Science Core Collection database. Visual maps were generated using CiteSpace and VOSviewer. We analyzed the included studies in terms of the annual publication count, countries, institutional affiliations, prolific authors, source journals, top 10 most cited articles, keyword co-occurrence, and cocitations.

RESULTS

A total of 525 papers examining the relationship between light and myopia published between 1981 and 2024 were collected. The United States ranked first in terms of the number of publications and actively engaged in international cooperation with other countries. The New England College of Optometry, which is located in the United States, was the most active institution and ranked first in terms of the number of publications. Schaeffel Frank was the most prolific author. The most active journal in the field was Investigative Ophthalmology & Visual Science. The most frequently cited paper in the included studies was written by Saw, SM and was published in 2002. The most common keywords in basic research included "refractive error," "longitudinal chromatic aberration," and "compensation." The most common keywords in clinical research mainly included "light exposure," "school," and "outdoor activity." The current research hotspots in this field are "progression," "refractive development," and "light exposure." The cocitation analysis generated 17 clusters.

CONCLUSION

This study is the first to use bibliometric methods to analyze existing research on the relationship between light and myopia. In recent years, the intensity and wavelength of light have become research hotspots in the field. Further research on light of different intensities and wavelengths may provide new perspectives in the future for designing more effective treatments and interventions to reduce the incidence of myopia.

Acupuncture modulates development of myopia by reducing NLRP3 inflammasome activation via the dopamine-D1R signaling pathway

BACKGROUND

Dopamine has been suggested to be a stop signal for eye growth and affects the development of myopia. Acupuncture is known to increase dopamine secretion and is widely used to treat myopia clinically.

OBJECTIVE

The aim of this study was to determine if acupuncture inhibits myopia progression in form deprived Syrian hamsters by inducing rises in dopamine content that in turn suppress inflammasome activation.

METHODS

Acupuncture was applied at LI4 and Taiyang every other day for 21 days. The levels of molecules associated with the dopamine signaling pathway, inflammatory signaling pathway and inflammasome activation were determined. A dopamine agonist (apomorphine) was used to evaluate if activation of the dopaminergic signaling pathway suppresses myopia progression by inhibiting inflammasome activation in primary retinal pigment epithelial (RPE) cells. A dopamine receptor 1 (D1R) inhibitor (SCH39166) was also administered to the hamsters.

RESULTS

Acupuncture inhibited myopia development by increasing dopamine levels and activating the D1R signaling pathway. Furthermore, we also demonstrated that nucleotide-binding oligomerization domain (NOD)-, leucine-rich repeat (LRR)- and pyrin domain-containing protein 3 (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome activation was inhibited by activation of the D1R signaling pathway.

CONCLUSION

Our findings suggest that acupuncture inhibits myopia development by suppressing inflammation, which is initiated by activation of the dopamine-D1R signaling pathway.

The Role of Retinal Dopamine D1 Receptors in Ocular Growth and Myopia Development in Mice

Dopamine is a key neurotransmitter in the signaling cascade controlling ocular refractive development, but the exact role and site of action of dopamine D1 receptors (D1Rs) involved in myopia remains unclear. Here, we determine whether retinal D1Rs exclusively mediate the effects of endogenous dopamine and systemically delivered D1R agonist or antagonist in the mouse form deprivation myopia (FDM) model. Male C57BL/6 mice subjected to unilateral FDM or unobstructed vision were divided into the following four groups: one noninjected and three groups that received intraperitoneal injections of a vehicle, D1R agonist SKF38393 (18 and 59 nmol/g), or D1R antagonist SCH39166 (0.1 and 1 nmol/g). The effects of these drugs on FDM were further assessed in Drd1-knock-out (Drd1-KO), retina-specific conditional Drd1-KO (Drd1-CKO) mice, and corresponding wild-type littermates. In the visually unobstructed group, neither SKF38393 nor SCH39166 affected normal refractive development, whereas myopia development was attenuated by SKF38393 and enhanced by SCH39166 injections. In Drd1-KO or Drd1-CKO mice, however, these drugs had no effect on FDM development, suggesting that activation of retinal D1Rs is pertinent to myopia suppression by the D1R agonist. Interestingly, the development of myopia was unchanged by either Drd1-KO or Drd1-CKO, and neither SKF38393 nor SCH39166 injections, nor Drd1-KO, affected the retinal or vitreal dopamine and the dopamine metabolite DOPAC levels. Effects on axial length were less marked than effects on refraction. Therefore, activation of D1Rs, specifically retinal D1Rs, inhibits myopia development in mice. These results also suggest that multiple dopamine D1R mechanisms play roles in emmetropization and myopia development.SIGNIFICANCE STATEMENT While dopamine is recognized as a "stop" signal that inhibits myopia development (myopization), the location of the dopamine D1 receptors (D1Rs) that mediate this action remains to be addressed. Answers to this key question are critical for understanding how dopaminergic systems regulate ocular growth and refraction. We report here the results of our study showing that D1Rs are essential for controlling ocular growth and myopia development in mice, and for identifying the retina as the site of action for dopaminergic control via D1Rs. These findings highlight the importance of intrinsic retinal dopaminergic mechanisms for the regulation of ocular growth and suggest specific avenues for exploring the retinal mechanisms involved in the dopaminergic control of emmetropization and myopization.

Effect of vascular endothelial growth factor 165 on dopamine level in the retinas of guinea pigs with form-deprivation myopia

Background

Myopia is the most common refractive error because excessive increase in the axial length of a myopic eye leads to the thinning of the posterior scleral pole and can cause serious complications resulting in blindness. Thus, myopia has become a great concern worldwide. Dopamine (DA) plays a role in the development of myopia. Moreover, in Parkinson's disease, it has been proved that vascular endothelial growth factor 165 (VEGF165) can promote the survival and recovery of DA neurons, resulting in increased DA secretion in the striatum, thereby treating neuropathy. Therefore, we speculate that VEGF165 can also promote the release of DA in the retina to inhibit the occurrence and development of myopia. We aimed to investigate the effect of VEGF165 on DA levels in the retinas of guinea pigs with form-deprivation myopia (FDM) and the effects of DA on myopia prevention and control.

Methods

Healthy 3-week-old pigmented guinea pigs were randomly divided into blank, FDM, phosphate buffer saline (PBS), 1, 5, and 10 ng groups. The FDM model was established by covering the right eye continuously with a translucent latex balloon pullover for 14 days. The pigs in the PBS, 1, 5, and 10 ng groups were injected with PBS buffer and 1, 5, and 10 ng of VEGF165 recombinant human protein, respectively, in the vitreous of the right eye before masking. The refractive error and axial length were measured before and after modeling. All retinas were used for biomolecular analyses after 14 days.

Results

We found that the intravitreal injection of VEGF165 elevated DA levels in the retina and was effective in slowing the progression of myopia, and 1 ng of VEGF165 was the most effective. Moreover, the number of vascular endothelial cell nuclei in the 1 ng group was lower than that in the other VEGF165 groups.

Conclusions

Our data suggest that VEGF165 has a promoting effect on DA in the retinas of guinea pigs with FDM, potentially controlling the development of myopia.

The Role of Retinal Dysfunction in Myopia Development

Myopia is a refractive disorder arising from a mismatch between refractive power and relatively long axial length of the eye. With its dramatically increasing prevalence, myopia has become a pervasive social problem. It is commonly accepted that abnormal visual input acts as an initiating factor of myopia. As the first station to perceive visual signals, the retina plays an important role in myopia etiology. The retina is a fine-layered structure with multitudinous cells, processing intricate visual signals via numerous molecular pathways. Accordingly, dopaminergic mechanisms, contributions of rod and cone photoreceptors, myopic structural changes of retinal pigment epithelium (RPE) and neuro-retinal layers have all suggested a vital role of retinal dysfunction in myopia development. Herein, we separately discuss myopia-related retinal dysfunction and current dilemmas by different levels, from molecules to cells, with the hope that the comprehensive delineation could contribute to a better understanding of myopia etiology, indicate novel therapeutic targets, and inspire future studies.

Durable recovery from amblyopia with donepezil

An elevated threshold for neuroplasticity limits visual gains with treatment of residual amblyopia in older children and adults. Acetylcholinesterase inhibitors (AChEI) can enable visual neuroplasticity and promote recovery from amblyopia in adult mice. Motivated by these promising findings, we sought to determine whether donepezil, a commercially available AChEI, can enable recovery in older children and adults with residual amblyopia. In this open-label pilot efficacy study, 16 participants (mean age 16 years; range 9-37 years) with residual anisometropic and/or strabismic amblyopia were treated with daily oral donepezil for 12 weeks. Donepezil dosage was started at 2.5 or 5.0 mg based on age and increased by 2.5 mg if the amblyopic eye visual acuity did not improve by 1 line from the visit 4 weeks prior for a maximum dosage of 7.5 or 10 mg. Participants < 18 years of age further patched the dominant eye. The primary outcome was visual acuity in the amblyopic eye at 22 weeks, 10 weeks after treatment was discontinued. Mean amblyopic eye visual acuity improved 1.2 lines (range 0.0-3.0), and 4/16 (25%) improved by ≥ 2 lines after 12 weeks of treatment. Gains were maintained 10 weeks after cessation of donepezil and were similar for children and adults. Adverse events were mild and self-limited. Residual amblyopia improves in older children and adults treated with donepezil, supporting the concept that the critical window of visual cortical plasticity can be pharmacologically manipulated to treat amblyopia. Placebo-controlled studies are needed.

Mice Lacking Gpr179 with Complete Congenital Stationary Night Blindness Are a Good Model for Myopia

Mutations in GPR179 are one of the most common causes of autosomal recessive complete congenital stationary night blindness (cCSNB). This retinal disease is characterized in patients by impaired dim and night vision, associated with other ocular symptoms, including high myopia. cCSNB is caused by a complete loss of signal transmission from photoreceptors to ON-bipolar cells. In this study, we hypothesized that the lack of Gpr179 and the subsequent impaired ON-pathway could lead to myopic features in a mouse model of cCSNB. Using ultra performance liquid chromatography, we show that adult Gpr179^-/- mice have a significant decrease in both retinal dopamine and 3,4-dihydroxyphenylacetic acid, compared to Gpr179^+/+ mice. This alteration of the dopaminergic system is thought to be correlated with an increased susceptibility to lens-induced myopia but does not affect the natural refractive development. Altogether, our data added a novel myopia model, which could be used to identify therapeutic interventions.

Altered Retinal Dopamine Levels in a Melatonin-proficient Mouse Model of Form-deprivation Myopia

Reduced levels of retinal dopamine, a key regulator of eye development, are associated with experimental myopia in various species, but are not seen in the myopic eyes of C57BL/6 mice, which are deficient in melatonin, a neurohormone having extensive interactions with dopamine. Here, we examined the relationship between form-deprivation myopia (FDM) and retinal dopamine levels in melatonin-proficient CBA/CaJ mice. We found that these mice exhibited a myopic refractive shift in form-deprived eyes, which was accompanied by altered retinal dopamine levels. When melatonin receptors were pharmacologically blocked, FDM could still be induced, but its magnitude was reduced, and retinal dopamine levels were no longer altered in FDM animals, indicating that melatonin-related changes in retinal dopamine levels contribute to FDM. Thus, FDM is mediated by both dopamine level-independent and melatonin-related dopamine level-dependent mechanisms in CBA/CaJ mice. The previously reported unaltered retinal dopamine levels in myopic C57BL/6 mice may be attributed to melatonin deficiency.

Regional Downregulation of Dopamine Receptor D1 in Bilateral Dorsal Lateral Geniculate Nucleus of Monocular Form-Deprived Amblyopia Models

Amblyopia is a common eye disease characterized by impaired best-corrected visual acuity. It starts in early childhood and leads to permanent vision reduction if left untreated. Even though many young patients with amblyopia are well treated in clinical practice, the underlying mechanism remains to be elucidated, which limits not only our understanding of this disease but also the therapeutic approach. To investigate the molecular mechanism of amblyopia, primate and rodent models of monocular-deprived amblyopia were created for mRNA screening and confirmation. We obtained 818 differentially expressed genes from the dorsal lateral geniculate nucleus (dLGN) of a primate model of amblyopia. After Gene Ontology and kyoto encyclopedia of genes and genomes (KEGG) enrichment analyses, the main enriched pathways were related to neural development. Interestingly, a particular neurotransmitter pathway, the dopaminergic pathway, was identified. The downregulation of dopamine receptor D1 (DRD1) was confirmed in both monkey and mouse samples. Furthermore, the immunofluorescence staining indicated that DRD1 expression was downregulated in both ventrolateral region of the contralateral dLGN and the dorsomedial region of the ipsilateral dLGN in the mouse model. The regions with downregulated expression of DRD1 were the downstream targets of the visual projection from the amblyopic eye. This study suggested that the downregulation of DRD1 in the LGN may be a cause for amblyopia. This may also be a reason for the failure of some clinical cases of levodopa combined with carbidopa applied to amblyopes.

Candidate pathways for retina to scleral signaling in refractive eye growth

The global prevalence of myopia, or nearsightedness, has increased at an alarming rate over the last few decades. An eye is myopic if incoming light focuses prior to reaching the retinal photoreceptors, which indicates a mismatch in its shape and optical power. This mismatch commonly results from excessive axial elongation. Important drivers of the myopia epidemic include environmental factors, genetic factors, and their interactions, e.g., genetic factors influencing the effects of environmental factors. One factor often hypothesized to be a driver of the myopia epidemic is environmental light, which has changed drastically and rapidly on a global scale. In support of this, it is well established that eye size is regulated by a homeostatic process that incorporates visual cues (emmetropization). This process allows the eye to detect and minimize refractive errors quite accurately and locally over time by modulating the rate of elongation of the eye via remodeling its outermost coat, the sclera. Critically, emmetropization is not dependent on post-retinal processing. Thus, visual cues appear to influence axial elongation through a retina-to-sclera, or retinoscleral, signaling cascade, capable of transmitting information from the innermost layer of the eye to the outermost layer. Despite significant global research interest, the specifics of retinoscleral signaling pathways remain elusive. While a few pharmacological treatments have proven to be effective in slowing axial elongation (most notably topical atropine), the mechanisms behind these treatments are still not fully understood. Additionally, several retinal neuromodulators, neurotransmitters, and other small molecules have been found to influence axial length and/or refractive error or be influenced by myopigenic cues, yet little progress has been made explaining how the signal that originates in the retina crosses the highly vascular choroid to affect the sclera. Here, we compile and synthesize the evidence surrounding three of the major candidate pathways receiving significant research attention - dopamine, retinoic acid, and adenosine. All three candidates have both correlational and causal evidence backing their involvement in axial elongation and have been implicated by multiple independent research groups across diverse species. Two hypothesized mechanisms are presented for how a retina-originating signal crosses the choroid - via 1) all-trans retinoic acid or 2) choroidal blood flow influencing scleral oxygenation. Evidence of crosstalk between the pathways is discussed in the context of these two mechanisms.

Alteration of EIF2 Signaling, Glycolysis, and Dopamine Secretion in Form-Deprived Myopia in Response to 1% Atropine Treatment: Evidence From Interactive iTRAQ-MS and SWATH-MS Proteomics Using a Guinea Pig Model

Purpose: Atropine, a non-selective muscarinic antagonist, effectively slows down myopia progression in human adolescents and several animal models. However, the underlying molecular mechanism is unclear. The current study investigated retinal protein changes of form-deprived myopic (FDM) guinea pigs in response to topical administration of 1% atropine gel (10 g/L).

Methods: At the first stage, the differentially expressed proteins were screened using fractionated isobaric tags for a relative and absolute quantification (iTRAQ) approach, coupled with nano-liquid chromatography-tandem mass spectrometry (nano-LC-MS/MS) (n = 24, 48 eyes) using a sample pooling technique. At the second stage, retinal tissues from another cohort with the same treatment (n = 12, 24 eyes) with significant ocular changes were subjected to label-free sequential window acquisition of all theoretical mass spectra (SWATH-MS) proteomics for orthogonal protein target confirmation. The localization of Alpha-synuclein was verified using immunohistochemistry and confocal imaging.

Results: A total of 1,695 proteins (8,875 peptides) were identified with 479 regulated proteins (FC ≥ 1.5 or ≤0.67) found from FDM eyes and atropine-treated eyes receiving 4-weeks drug treatment using iTRAQ-MS proteomics. Combining the iTRAQ-MS and SWATH-MS datasets, a total of 29 confident proteins at 1% FDR were consistently quantified and matched, comprising 12 up-regulated and 17 down-regulated proteins which differed between FDM eyes and atropine treated eyes (iTRAQ: FC ≥ 1.5 or ≤0.67, SWATH: FC ≥ 1.4 or ≤0.71, p-value of ≤0.05). Bioinformatics analysis using IPA and STRING databases of these commonly regulated proteins revealed the involvement of the three commonly significant pathways: EIF2 signaling; glycolysis; and dopamine secretion. Additionally, the most significantly regulated proteins were closely connected to Alpha-synuclein (SNCA). Using immunostaining (n = 3), SNCA was further confirmed in the inner margin of the inner nuclear layer (INL) and spread throughout the inner plexiform layer (IPL) of the retina of guinea pigs.

Conclusion: The molecular evidence using next-generation proteomics (NGP) revealed that retinal EIF2 signaling, glycolysis, and dopamine secretion through SNCA are implicated in atropine treatment of myopia in the FDM-induced guinea pig model.

Retinal Dopamine D2 Receptors Participate in the Development of Myopia in Mice

Purpose

To learn more about the locations of dopamine D2 receptors (D2Rs) that regulate form-deprivation myopia (FDM), using different transgenic mouse models.

Methods

One eye of D2R-knockout (KO) mice and wild-type littermates was subjected to four weeks of monocular FDM, whereas the fellow eye served as control. Mice in both groups received daily intraperitoneal injections of either the D2R antagonist sulpiride (8 µg/g) or vehicle alone. FDM was also induced in retina- (Six3^creD2R^fl/fl) or fibroblast-specific (S100a4^creD2R^fl/fl) D2R-KO mice. A subset of retina-specific D2R-KO mice and D2R^fl/fl littermates were also given sulpiride or vehicle injections. Refraction was measured with an eccentric infrared photorefractor, and other biometric parameters were measured by optical coherence tomography (n ≈ 20 for each group).

Results

FDM development was attenuated in wild-type littermates treated with sulpiride. However, this inhibitory effect disappeared in the D2R-KO mice, suggesting that antagonizing D2Rs suppressed myopia development. Similarly, the development of myopia was partially inhibited by retina-specific (deletion efficiency: 94.7%) but not fibroblast-specific (66.9%) D2R-KO. The sulpiride-mediated inhibitory effects on FDM also disappeared with retinal D2R-KO, suggesting that antagonizing D2Rs outside the retina may not attenuate myopia. Changes in axial length were less marked than changes in refraction, but in general the two were correlated.

Conclusions

This study demonstrates that D2Rs located in the retina participate in dopaminergic regulation of FDM in mice. These findings provide an important and fundamental basis for further exploring the retinal mechanism(s) involved in dopamine signaling and myopia development.

Management of amblyopia in pediatric patients: Current insights

Amblyopia is a cause of significant ocular morbidity in pediatric population and may lead to visual impairment in future life. It is caused due to formed visual deprivation or abnormal binocular interactions. Several risk factors in pediatric age group may lead to this disease. Author groups have tried managing different types of amblyopia, like anisometropic amblyopia, strabismic amblyopia and combined mechanism amblyopia, with optical correction, occlusion therapy, penalization, binocular therapy and surgery. We review historical and current management strategies of different types of amblyopia affecting children and outcomes in terms of visual acuity, binocularity and ocular deviation, highlighting evidence from recent studies. Literature searches were performed through Pubmed. Risk factors for amblyopia need to be identified in pediatric population as early in life as possible and managed accordingly, as visual outcomes in amblyopia are best if treated at the earliest. Although, monocular therapies like occlusion or penalization have been shown to be quite beneficial over the years, newer concepts related to binocular vision therapy are still evolving.

Melanopsin modulates refractive development and myopia

Myopia, or nearsightedness, is the most common form of refractive abnormality and is characterized by excessive ocular elongation in relation to ocular power. Retinal neurotransmitter signaling, including dopamine, is implicated in myopic ocular growth, but the visual pathways that initiate and sustain myopia remain unclear. Melanopsin-expressing retinal ganglion cells (mRGCs), which detect light, are important for visual function, and have connections with retinal dopamine cells. Here, we investigated how mRGCs influence normal and myopic refractive development using two mutant mouse models: Opn4-/- mice that lack functional melanopsin photopigments and intrinsic mRGC responses but still receive other photoreceptor-mediated input to these cells; and Opn4DTA/DTA mice that lack intrinsic and photoreceptor-mediated mRGC responses due to mRGC cell death. In mice with intact vision or form-deprivation, we measured refractive error, ocular properties including axial length and corneal curvature, and the levels of retinal dopamine and its primary metabolite, L-3,4-dihydroxyphenylalanine (DOPAC). Myopia was measured as a myopic shift, or the difference in refractive error between the form-deprived and contralateral eyes. We found that Opn4-/- mice had altered normal refractive development compared to Opn4+/+ wildtype mice, starting ∼4D more myopic but developing ∼2D greater hyperopia by 16 weeks of age. Consistent with hyperopia at older ages, 16 week-old Opn4-/- mice also had shorter eyes compared to Opn4+/+ mice (3.34 vs 3.42 mm). Opn4DTA/DTA mice, however, were more hyperopic than both Opn4+/+ and Opn4-/- mice across development ending with even shorter axial lengths. Despite these differences, both Opn4-/- and Opn4DTA/DTA mice had ∼2D greater myopic shifts in response to form-deprivation compared to Opn4+/+ mice. Furthermore, when vision was intact, dopamine and DOPAC levels were similar between Opn4-/- and Opn4+/+ mice, but higher in Opn4DTA/DTA mice, which differed with age. However, form-deprivation reduced retinal dopamine and DOAPC by ∼20% in Opn4-/- compared to Opn4+/+ mice but did not affect retinal dopamine and DOPAC in Opn4DTA/DTA mice. Lastly, systemically treating Opn4-/- mice with the dopamine precursor L-DOPA reduced their form-deprivation myopia by half compared to non-treated mice. Collectively our findings show that disruption of retinal melanopsin signaling alters the rate and magnitude of normal refractive development, yields greater susceptibility to form-deprivation myopia, and changes dopamine signaling. Our results suggest that mRGCs participate in the eye's response to myopigenic stimuli, acting partly through dopaminergic mechanisms, and provide a potential therapeutic target underling myopia progression. We conclude that proper mRGC function is necessary for correct refractive development and protection from myopia progression.

Visually induced changes in cytokine production in the chick choroid

Postnatal ocular growth is regulated by a vision-dependent mechanism that acts to minimize refractive error through coordinated growth of the ocular tissues. Of great interest is the identification of the chemical signals that control visually guided ocular growth. Here, we provide evidence that the pro-inflammatory cytokine, interleukin-6 (IL-6), may play a pivotal role in the control of ocular growth using a chicken model of myopia. Microarray, real-time RT-qPCR, and ELISA analyses identified IL-6 upregulation in the choroids of chick eyes under two visual conditions that introduce myopic defocus and slow the rate of ocular elongation (recovery from induced myopia and compensation for positive lenses). Intraocular administration of atropine, an agent known to slow ocular elongation, also resulted in an increase in choroidal IL-6 gene expression. Nitric oxide appears to directly or indirectly upregulate choroidal IL-6 gene expression, as administration of the non-specific nitric oxide synthase inhibitor, L-NAME, inhibited choroidal IL-6 gene expression, and application of a nitric oxide donor stimulated IL-6 gene and protein expression in isolated chick choroids. Considering the pleiotropic nature of IL-6 and its involvement in many biological processes, these results suggest that IL-6 may mediate many aspects of the choroidal response in the control of ocular growth.

OCT-Angiography Findings in Patients with Amblyopia: Comparison between Healthy Controls, Treatment-Responsive, and Treatment-Unresponsive Amblyopic Patients

There is no consensus on whether amblyopia affects the retinal vascular plexus and morphology. Previous studies focused on the differences between amblyopic patients and normal controls without evaluating amblyopic eyes after patching. To evaluate differences in the superficial vascular density of amblyopic eyes, normal eyes, and amblyopic eyes reaching normal BCVA after patch therapy, OCTA was used. All patients underwent a comprehensive ophthalmological examination, including visual acuity, refraction, ocular motility tests, and anterior and posterior segment examination. OCTA was performed by an expert physician using the Zeiss Cirrus 5000-HD-OCT Angioplex (Carl Zeiss, Meditec, Inc., Dublin, OH, USA). OCTA scans were performed using a 3 × 3 mm² and 6 × 6 mm² fovea-centered image setting. The mean outer macular vessel density in the previously amblyopic group was 19.15 ± 0.51%. This was statistically significantly higher than in both the amblyopic group (18.70 ± 1.14%) and the normal controls (18.18 ± 1.40%) (p = 0.014). The previously amblyopic group also significantly differed from both normal controls and amblyopic eyes with regards to the inner (p = 0.011), outer (p = 0.006), and full (p = 0.003) macular perfusion. Finally, linear regression analysis revealed that BCVA was linearly correlated to outer perfusion in amblyopic (p = 0.003) and ex amblyopic eyes (p < 0.001). Considering the cross-sectional nature of our study, from our results, we can only hypothesize a possible correlation between light stimulation and retinal vasculature development. However, further longitudinal studies are needed to support this hypothesis.

Young adults with myopia have lower concentrations of neuromodulators-dopamine and melatonin in serum and tear

The purpose of this experimental case-control study was to explore the association between myopia and concentration of dopamine and melatonin in serum and tear fluid among young myopic adults, compared to age matched non-myopic controls. Healthy myopic adults with Spherical equivalent refraction (SER) of ≤ -0.50 D to -6.00 D and emmetropic adults were included in the study. All participants underwent comprehensive eye examination and ocular biometric measures that included-axial length and corneal radii. Insomnia symptom questionnaire (ISQ) was used to screen the symptoms associated with the diagnostic criteria for primary insomnia. Morning serum and tear concentration of dopamine and melatonin were collected and was quantified using High performance liquid chromatography. A total number of 40 participants, 21 myopes and 19 controls, with a median (IQR) age of myopes 24 [21-34] years and controls 24 [20-29] years were studied. The Median [IQR] of SER was -2.00[-6.25-(-0.50)] D and 0 [(-0.50)-0.25] D for myopes and controls respectively. Myopes were found to have significantly lower concentration of serum dopamine (Median [IQR]) 190 [50-342] ng/mL compared to controls (Median [IQR]) 411 [84-717] ng/mL (U = 88, p < 0.002). Likewise, myopes showed significantly lower serum melatonin concentration of 40 [20-169] ng/mL compared to controls 203 [22-539] ng/mL (U = 88.50, p < 0.001). Myopes exhibited lower concentration of tear dopamine 101 [8-188] ng/mL compared to controls 136 [25-451] ng/mL (U = 103, p < 0.05). Likewise, myopes showed significantly lower tear melatonin concentration 6 [2-18] ng/mL compared to controls 9 [2-23] ng/mL (U = 104, p < 0.05). Both serum dopamine (r = 0.419, p < 0.05) and melatonin (r = 0.323, p < 0.05) showed significant positive association with increase in spherical equivalent refraction (SER). The observed changes in the decreased concentration of Dopamine and Melatonin among young adult myopes and its association with refraction indicates the role of altered circadian rhythm in the human myopia mechanism.

Form-Deprivation and Lens-Induced Myopia Are Similarly Affected by Pharmacological Manipulation of the Dopaminergic System in Chicks

Purpose

Animal models have demonstrated a link between decreases in retinal dopamine levels and the development of form-deprivation myopia (FDM). However, the consistency of dopamine's role in the other major form of experimental myopia, that of lens-induced myopia (LIM), is less clear, raising the question as to what extent dopamine plays a role in human myopia. Therefore, to better define the role of dopamine in both forms of experimental myopia, we examined how consistent the protection afforded by dopamine and the dopamine agonist 6-amino-5,6,7,8-tetrahydronaphthalene-2,3-diol hydrobromide (ADTN) is between FDM and LIM.

Methods

Intravitreal injections of dopamine (0.002, 0.015, 0.150, 1.500 µmol) or ADTN (0.001, 0.010, 0.100, 1.000 µmol) were administered daily to chicks developing FDM or LIM. Axial length and refraction were measured following 4 days of treatment. To determine the receptor subtype by which dopamine and ADTN inhibit FDM and LIM, both compounds were coadministered with either the dopamine D2-like antagonist spiperone (0.005 µmol) or the D1-like antagonist SCH-23390 (0.005 µmol).

Results

Intravitreal administration of dopamine or ADTN inhibited the development of FDM (ED₅₀ = 0.003 µmol and ED₅₀ = 0.011 µmol, respectively) and LIM (ED₅₀ = 0.002 µmol and ED₅₀ = 0.010 µmol, respectively) in a dose-dependent manner, with a similar degree of protection observed in both paradigms (P = 0.471 and P = 0.969, respectively). Coadministration with spiperone, but not SCH-23390, inhibited the protective effects of dopamine and ADTN against the development of both FDM (P = 0.214 and P = 0.138, respectively) and LIM (P = 0.116 and P = 0.100, respectively).

Conclusions

pharmacological targeting of the retinal dopamine system inhibits FDM and LIM in a similar dose-dependent manner through a D2-like mechanism.

The Role of the Dopamine D2 Receptor in Form-Deprivation Myopia in Mice: Studies With Full and Partial D2 Receptor Agonists and Knockouts

Purpose

The purpose of this study was to explore the role and mechanism of D2 receptor (D2R) involvement in myopia development and the effects of the full D2R agonist quinpirole and partial D2R agonist aripiprazole on postnatal refractive development and form-deprivation myopia (FDM).

Methods

C57BL/6 (“B6”) mice, raised either in a visually normal or unilateral form-deprivation environment, were divided into three subgroups, including an intraperitoneally injected (IP) vehicle group and two quinpirole (1 and 10 µg/g body weight) treatment groups. The effects of quinpirole on FDM were further verified in D2R-knockout (KO) mice and corresponding wild-type littermates. Then, the modulation of normal vision development and FDM by aripiprazole (1 and 10 µg/g body weight, IP) was assessed in C57BL/6 mice. All biometric parameters were measured before and after treatments, and retinal cyclic adenosine phosphate (cAMP) and phosphorylated ERK (pERK) levels were analyzed to assess D2R-mediated signal transduction.

Results

Neither quinpirole nor aripiprazole affected normal refractive development. FDM development was inhibited by quinpirole at low dose but enhanced at high dose, and these bidirectional effects were validated by D2R-specificity. FDM development was attenuated by the partial D2R agonist aripiprazole, at high dose but not at low dose. Quinpirole caused a dose-dependent reduction in cAMP levels, but had no effect on pERK. Aripiprazole reduced cAMP levels at both doses, but caused a dose-dependent increase of pERK in the form-deprived eyes.

Conclusions

Reduction of D2R-mediated signaling contributes to myopia development, which can be selectively attenuated by partial D2R agonists that activate D2Rs under the low dopamine levels that occur with FDM.

Ambient Light Regulates Retinal Dopamine Signaling and Myopia Susceptibility

Purpose

Exposure to high-intensity or outdoor lighting has been shown to decrease the severity of myopia in both human epidemiological studies and animal models. Currently, it is not fully understood how light interacts with visual signaling to impact myopia. Previous work performed in the mouse retina has demonstrated that functional rod photoreceptors are needed to develop experimentally-induced myopia, alluding to an essential role for rod signaling in refractive development.

Methods

To determine whether dim rod-dominated illuminance levels influence myopia susceptibility, we housed male C57BL/6J mice under 12:12 light/dark cycles with scotopic (1.6 × 10⁻³ candela/m²), mesopic (1.6 × 10¹ cd/m²), or photopic (4.7 × 10³ cd/m²) lighting from post-natal day 23 (P23) to P38. Half the mice received monocular exposure to −10 diopter (D) lens defocus from P28–38. Molecular assays to measure expression and content of DA-related genes and protein were conducted to determine how illuminance and lens defocus alter dopamine (DA) synthesis, storage, uptake, and degradation and affect myopia susceptibility in mice.

Results

We found that mice exposed to either scotopic or photopic lighting developed significantly less severe myopic refractive shifts (lens treated eye minus contralateral eye; –1.62 ± 0.37D and −1.74 ± 0.44D, respectively) than mice exposed to mesopic lighting (–3.61 ± 0.50D; P < 0.005). The 3,4-dihydroxyphenylacetic acid /DA ratio, indicating DA activity, was highest under photopic light regardless of lens defocus treatment (controls: 0.09 ± 0.011 pg/mg, lens defocus: 0.08 ± 0.008 pg/mg).

Conclusions

Lens defocus interacted with ambient conditions to differentially alter myopia susceptibility and DA-related genes and proteins. Collectively, these results show that scotopic and photopic lighting protect against lens-induced myopia, potentially indicating that a broad range of light levels are important in refractive development.

Pharmacotherapeutic candidates for myopia: A review

This review provides insights into the mechanism underlying the pathogenesis of myopia and potential targets for clinical intervention. Although the etiology of myopia involves both environmental and genetic factors, recent evidence has suggested that the prevalence and severity of myopia appears to be affected more by environmental factors. Current pharmacotherapeutics are aimed at inhibiting environmentally induced changes in visual input and subsequent changes in signaling pathways during myopia pathogenesis and progression. Recent studies on animal models of myopia have revealed specific molecules potentially involved in the regulation of eye development. Among them, the dopamine receptor plays a critical role in controlling myopia. Subsequent studies have reported pharmacotherapeutic treatments to control myopia progression. In particular, atropine treatment yielded favorable outcomes and has been extensively used; however, current studies are aimed at optimizing its efficacy and confirming its safety. Furthermore, future studies are required to assess the efficacy of combinatorial use of low-dose atropine and contact lenses or orthokeratology.

Light and myopia: from epidemiological studies to neurobiological mechanisms

Myopia is far beyond its inconvenience and represents a true, highly prevalent, sight-threatening ocular condition, especially in Asia. Without adequate interventions, the current epidemic of myopia is projected to affect 50% of the world population by 2050, becoming the leading cause of irreversible blindness. Although blurred vision, the predominant symptom of myopia, can be improved by contact lenses, glasses or refractive surgery, corrected myopia, particularly high myopia, still carries the risk of secondary blinding complications such as glaucoma, myopic maculopathy and retinal detachment, prompting the need for prevention. Epidemiological studies have reported an association between outdoor time and myopia prevention in children. The protective effect of time spent outdoors could be due to the unique characteristics (intensity, spectral distribution, temporal pattern, etc.) of sunlight that are lacking in artificial lighting. Concomitantly, studies in animal models have highlighted the efficacy of light and its components in delaying or even stopping the development of myopia and endeavoured to elucidate possible mechanisms involved in this process. In this narrative review, we (1) summarize the current knowledge concerning light modulation of ocular growth and refractive error development based on studies in human and animal models, (2) summarize potential neurobiological mechanisms involved in the effects of light on ocular growth and emmetropization and (3) highlight a potential pathway for the translational development of noninvasive light-therapy strategies for myopia prevention in children.

Topical application of dopaminergic compounds can inhibit deprivation myopia in chicks

PURPOSE

Animal models have demonstrated a link between dysregulation of the retinal dopamine system and the development of experimental myopia (short-sightedness). However, pharmacological investigations of dopamine in animal models rely heavily on intravitreal or systemic administration, which have several limitations for longer-term experiments. We therefore investigated whether administration of dopamine as a topical eye drop can inhibit the development of form-deprivation myopia (FDM) in chicks. We also examined whether chemical modification of dopamine through deuterium substitution, which might enhance stability and bioavailability, can increase dopamine's effectiveness against FDM when given topically.

METHODS

Dopamine or deuterated dopamine (Dopamine-1,1,2,2-d₄ hydrochloride) was administered as a daily intravitreal injection or as daily topical eye drops to chicks developing FDM over an ascending dose range (min. n = 6 per group). Axial length and refraction were measured following 4 days of treatment.

RESULTS

Both intravitreal (ED₅₀ = 0.002μmoles) and topical application (ED₅₀ = 6.10μmoles) of dopamine inhibited the development of FDM in a dose-dependent manner. Intravitreal injections, however, elicited a significantly higher level of protection relative to topical eye drops (p < 0.01). Deuterated dopamine inhibited FDM to a similar extent as unmodified dopamine when administered as intravitreal injections (p = 0.897) or topical eye drops (p = 0.921).

CONCLUSIONS

Both intravitreal and topical application of dopamine inhibit the development of FDM in a dose-dependent manner, indicating that topical administration may be an effective avenue for longer-term dopamine experiments. Deuterium substitution does not alter the protection afforded by dopamine against FDM when given as either an intravitreal injection or topical eye drop.

Visual conditions affecting eye growth alter diurnal levels of vitreous DOPAC

In chicks, the diurnal patterns of retinal dopamine synthesis and release are associated with refractive development. To assess the within-day patterns of dopamine release, we assayed vitreal levels of DOPAC (3,4-dihydroxyphenylacetic acid) using high performance liquid chromatography with electrochemical detection, at 4-h intervals over 24 h in eyes with experimental manipulations that change ocular growth rates. Chicks were reared under a 12 h light/12 h dark cycle; experiments began at 12 days of age. Output was assessed by modelling using the robust variance structure of Generalized Estimating Equations. Continuous spectacle lensdefocus or form deprivation: One group experienced non-restricted visual input to both eyes and served as untreated "normal" controls. Three experimental cohorts underwent monocular visual alterations known to alter eye growth and refraction: wearing a diffuser, a negative lens or a positive lens. After one full day of device-wear, chicks were euthanized at 4-h intervals over 24 h (8 birds per time/condition). Brief hyperopic defocus: Chicks wore negative lenses for only 2 daily hours either in the morning (starting at ZT 0; n = 16) or mid-day (starting at ZT 4; n = 8) for 3 days. Vitreal DOPAC was assayed. In chicks with bilateral non-restricted vision, or with continuous defocus or form-deprivation, there was a diurnal variation in vitreal DOPAC levels for all eyes (p < 0.001 for each). In normal controls, DOPAC was highest during the daytime, lowest at night, and equivalent for both eyes. In experimental groups, regardless of whether experiencing a growth stimulatory input (diffuser; negative lens) or growth inhibitory input (positive lens), DOPAC levels were reduced compared both to fellow eyes and to those of normal controls (p < 0.001 for each). These diurnal variations in vitreous DOPAC levels under different visual conditions indicate a complexity for dopaminergic mechanisms in refractive development that requires further study.

An update on pharmacological treatment options for amblyopia

Amblyopia is a common cause of visual impairment in children and young adults. The cornerstone in the management of this disorder is based on increasing visual stimulation of the amblyopic eye by occlusion, by administering atropine or by causing optical penalization of the dominant eye. All these treatment options have shown some limits in terms of efficacy, due to the suboptimal treatment adherence for the patients and the lack of long-term clinical outcomes. Moreover, although it is well known that clinical efficacy decreases with age, new evidence is suggesting that cortical plasticity can be induced also in older children. For these reasons, new treatment options are being studied, in order to extend the "treatment window" beyond the critical period also in older patients. In this review, we will discuss all the most promising novel pharmacological agents in the management of amblyopia.

A prospective study of serum metabolomic and lipidomic changes in myopic children and adolescents

BACKGROUND

Myopia is a prevalent eye disorder, especially among children and adolescents in eastern Asian countries. Multiple measures have already been taken to prevent and treat myopia, including atropine and dopamine. However, the serum metabolic picture of myopia has not yet been studied as a whole and remains largely unclear. In this paper, a prospective and panoramic study was carried out to find out the whole serum metabolomic and lipidomic picture of myopia.

METHODS

With untargeted mass spectrometry (MS), myopia among 211 children and adolescents was studied. The MS features were first grouped across the samples. Then, compound annotation was carried out based on these features. Finally, the metabolite features were mapped to pathways, whose biological functions in myopia were studied and discussed.

RESULTS

A total of 275 metabolite features were derived from 92 aligned MS peak groups with significant fold changes, and then mapped to 33 pathways. By a comprehensive consideration of significance, fold change, importance score and appearance in different omics, 9 pathways were selected, and their biological functions were further analyzed. Among these selected pathways, 5 pathways were related with oxidative stress, a validated phenomenon during myopia development, while 5 pathways were related with dopamine receptor D2, whose molecular function in myopia treatment is not fully understood. A total of 177 metabolite features from 45 peak groups were related with the studied pathways.

CONCLUSION

This prospective study shed light on the whole picture of metabolomic mechanism underlying myopia and provided guidance to further elucidation of compounds and pathways in this whole picture.

Levodopa inhibits the development of lens-induced myopia in chicks

Animal models have demonstrated a link between dysregulation of the retinal dopamine system and the development of myopia (short-sightedness). We have previously demonstrated that topical application of levodopa in chicks can inhibit the development of form-deprivation myopia (FDM) in a dose-dependent manner. Here, we examine whether this same protection is observed in lens-induced myopia (LIM), and whether levodopa’s protection against FDM and LIM occurs through a dopamine D1- or D2-like receptor mechanism. To do this, levodopa was first administered daily as an intravitreal injection or topical eye drop, at one of four ascending doses, to chicks developing LIM. Levodopa’s mechanism of action was then examined by co-administration of levodopa injections with D1-like (SCH-23390) or D2-like (spiperone) dopamine antagonists in chicks developing FDM or LIM. For both experiments, levodopa’s effectiveness was examined by measuring axial length and refraction after 4 days of treatment. Levodopa inhibited the development of LIM in a dose-dependent manner similar to its inhibition of FDM when administered via intravitreal injections or topical eye drops. In both FDM and LIM, levodopa injections remained protective against myopia when co-administered with SCH-23390, but not spiperone, indicating that levodopa elicits its protection through a dopamine D2-like receptor mechanism in both paradigms.

Current Management of Childhood Amblyopia

Amblyopia is defined as the reduction of best-corrected visual acuity of one or both eyes caused by conditions that affect normal visual development. The basic strategy to treat amblyopia is to obtain a clear retinal image in each eye and correct ocular dominance through forced use of the amblyopic eye. Treatment modalities include correcting any underlying organic disease, prescribing appropriate optical correction, and providing occlusion/penalization therapy for the non-amblyopic eye. Given the success of amblyopia treatment declines with increasing age, the detection and management of amblyopia should begin as early as possible during the sensitive period for visual development. Proper management of amblyopia during childhood can reduce the overall prevalence and severity of visual loss. This study aims to provide an update for the management of childhood amblyopia to provide better visual outcomes.

Pathogenesis and Prevention of Worsening Axial Elongation in Pathological Myopia

PURPOSE

This review discusses the etiology and pathogenesis of myopia, prevention of disease progression and worsening axial elongation, and emerging myopia treatment modalities.

INTRODUCTION

Pediatric myopia is a public health concern that impacts young children worldwide and is associated with numerous future ocular diseases such as cataract, glaucoma, retinal detachment and other chorioretinal abnormalities. While the exact mechanism of myopia of the human eye remains obscure, several studies have reported on the role of environmental and genetic factors in the disease development.

METHODS

A review of literature was conducted. PubMed and Medline were searched for combinations and derivatives of the keywords including, but not limited to, "pediatric myopia", "axial elongation", "scleral remodeling" or "atropine." The PubMed and Medline database search were performed for randomized control trials, systematic reviews and meta-analyses using the same keyword combinations.

RESULTS

Studies have reported that detection of genetic correlations and modification of environmental influences may have a significant impact in myopia progression, axial elongation and future myopic ocular complications. The conventional pharmacotherapy of pediatric myopia addresses the improvement in visual acuity and prevention of amblyopia but does not affect axial elongation or myopia progression. Several studies have published varying treatments, including optical, pharmacological and surgical management, which show great promise for a more precise control of myopia and preservation of ocular health.

DISCUSSION

Understanding the role of factors influencing the onset and progression of pediatric myopia will facilitate the development of successful treatments, reduction of disease burden, arrest of progression and improvement in future of the management of myopia.

Simplified updates on the pathophysiology and recent developments in the treatment of amblyopia: A review

Amblyopia is the most common cause of monocular visual impairment affecting 2-5% of the general population. Amblyopia is a developmental cortical disorder of the visual pathway essentially due to abnormal visual stimulus, reaching the binocular cortical cells, which may be multivariate. Ganglion cells are of two types: parvocellular (P cells) and magnocellular (M cells); they are the first step where the light energy is converted in to neural impulse. P cells are involved in fine visual acuity, fine stereopsis, and color vision and M cells are involved in gross stereopsis and movement recognition. Strabismus, refractive error, cataract, and ptosis, occurring during critical period are highly amblyogenic. The critical period extends from birth to 7--8 years. The earlier the clinically significant refractive error and strabismus are detected and treated, the greater the likelihood of preventing amblyopia. Treatment for amblyopia in children includes: optical correction of significant refractive errors, patching, pharmacological treatment, and alternative therapies which include: vision therapy, binocular therapy, and liquid crystal display eyeglasses are newer treatment modalities for amblyopia. Age of starting the treatment is not predictive of outcome, instituting treatment on detection and early detection plays a role in achieving better outcomes. This review aims to give a simplified update on amblyopia, which will be of use to a clinician, in understanding the pathophysiology of the complex condition. We also share the cortical aspects of amblyopia and give recent developments in the treatment of amblyopia.

Effectiveness and safety of topical levodopa in a chick model of myopia

Animal models have demonstrated a link between dysregulation of the retinal dopamine system and the excessive ocular growth associated with the development of myopia. Here we show that intravitreal or topical application of levodopa, which is widely used in the treatment of neurological disorders involving dysregulation of the dopaminergic system, inhibits the development of experimental myopia in chickens. Levodopa slows ocular growth in a dose dependent manner in chicks with a similar potency to atropine, a common inhibitor of ocular growth in humans. Topical levodopa remains effective over chronic treatment periods, with its effectiveness enhanced by coadministration with carbidopa to prevent its premature metabolism. No changes in normal ocular development (biometry and refraction), retinal health (histology), or intraocular pressure were observed in response to chronic treatment (4 weeks). With a focus on possible clinical use in humans, translation of these avian safety findings to a mammalian model (mouse) illustrate that chronic levodopa treatment (9 months) does not induce any observable changes in visual function (electroretinogram recordings), ocular development, and retinal health, suggesting that levodopa may have potential as a therapeutic intervention for human myopia.

Ocular and Systemic Diurnal Rhythms in Emmetropic and Myopic Adults

Purpose

To investigate ocular and systemic diurnal rhythms in emmetropic and myopic adults and examine relationships with light exposure.

Methods

Adult subjects (n = 42, 22–41 years) underwent measurements every 4 hours for 24 hours, including blood pressure, heart rate, body temperature, intraocular pressure (IOP), ocular biometry, and optical coherence tomography imaging. Mean ocular perfusion pressure (MOPP) was calculated. Saliva was collected for melatonin and cortisol analysis. Acrophase and amplitude for each parameter were compared between refractive error groups. Subjects wore a light, sleep, and activity monitor for 1 week before measurements.

Results

All parameters exhibited significant diurnal rhythm (ANOVA, P < 0.05 for all). Choroidal thickness peaked at 2.42 hours, with a diurnal variation of 25.8 ± 13.44 μm. Axial length peaked at 12.96 hours, with a variation of 35.71 ± 6.6 μm. Melatonin peaked at 3.19 hours during the dark period, while cortisol peaked after light onset at 8.86 hours. IOP peaked at 11.24 hours, with a variation of 4.92 ± 1.57 mm Hg, in antiphase with MOPP, which peaked at 22.02 hours. Amplitudes of daily variations were not correlated with light exposure, and rhythms were not significantly different between emmetropes and myopes, except for body temperature and MOPP.

Conclusions

Diurnal variations in ocular and systemic parameters were observed in young adults; however, these variations were not associated with habitual light exposure. Emmetropic and myopic refractive error groups showed small but significant differences in body temperature and MOPP, while other ocular and systemic patterns were similar.

Integrated assessment of visual perception abnormalities in psychotic disorders and relationship with clinical characteristics

BACKGROUND

The visual system is recognized as an important site of pathology and dysfunction in schizophrenia. In this study, we evaluated different visual perceptual functions in patients with psychotic disorders using a potentially clinically applicable task battery and assessed their relationship with symptom severity in patients, and with schizotypal features in healthy participants.

METHODS

Five different areas of visual functioning were evaluated in patients with schizophrenia and schizoaffective disorder (n = 28) and healthy control subjects (n = 31) using a battery that included visuospatial working memory (VSWM), velocity discrimination (VD), contour integration, visual context processing, and backward masking tasks.

RESULTS

The patient group demonstrated significantly lower performance in VD, contour integration, and VSWM tasks. Performance did not differ between the two groups on the visual context processing task and did not differ across levels of interstimulus intervals in the backward masking task. Performances on VSWM, VD, and contour integration tasks were correlated with negative symptom severity but not with other symptom dimensions in the patient group. VSWM and VD performances were also correlated with negative sychizotypal features in healthy controls.

CONCLUSION

Taken together, these results demonstrate significant abnormalities in multiple visual processing tasks in patients with psychotic disorders, adding to the literature implicating visual abnormalities in these conditions. Furthermore, our results show that visual processing impairments are associated with the negative symptom dimension in patients as well as healthy individuals.

Current and emerging pharmaceutical interventions for myopia

Myopia is a major cause of visual impairment. Its prevalence is growing steadily, especially in East Asia. Despite the immense disease and economic burden, there are currently no Food and Drug Administration-approved drugs for myopia. This review aims to summarise pharmaceutical interventions of myopia at clinical and preclinical stages in the last decade and discuss challenges for preclinical myopia drugs to progress to clinical trials. Atropine and oral 7-methylxanthine are shown to reduce myopia progression in human studies. The former has been extensively studied and is arguably the most successful medication. However, it has side effects and trials on low-dose atropine are ongoing. Other pharmaceutical agents being investigated at a clinical trial level include ketorolac tromethamine, oral riboflavin and BHVI2 (an experimental drug). Since the pathophysiology of myopia is not fully elucidated, numerous drugs have been tested at the preclinical stage and can be broadly categorised based on the proposed mechanisms of myopisation, namely antimuscarinic, dopaminergic, anti-inflammatory and more. However, several agents were injected intravitreally or subconjunctivally, hindering their progress to human trials. Furthermore, with atropine being the most successful medication available, future preclinical interventions should be studied in combination with atropine to optimise the treatment of myopia.

IMI - Report on Experimental Models of Emmetropization and Myopia

The results of many studies in a variety of species have significantly advanced our understanding of the role of visual experience and the mechanisms of postnatal eye growth, and the development of myopia. This paper surveys and reviews the major contributions that experimental studies using animal models have made to our thinking about emmetropization and development of myopia. These studies established important concepts informing our knowledge of the visual regulation of eye growth and refractive development and have transformed treatment strategies for myopia. Several major findings have come from studies of experimental animal models. These include the eye's ability to detect the sign of retinal defocus and undergo compensatory growth, the local retinal control of eye growth, regulatory changes in choroidal thickness, and the identification of components in the biochemistry of eye growth leading to the characterization of signal cascades regulating eye growth and refractive state. Several of these findings provided the proofs of concepts that form the scientific basis of new and effective clinical treatments for controlling myopia progression in humans. Experimental animal models continue to provide new insights into the cellular and molecular mechanisms of eye growth control, including the identification of potential new targets for drug development and future treatments needed to stem the increasing prevalence of myopia and the vision-threatening conditions associated with this disease.

New advances in amblyopia therapy I: binocular therapies and pharmacologic augmentation

Amblyopia therapy options have traditionally been limited to penalisation of the non-amblyopic eye with either patching or pharmaceutical penalisation. Solid evidence, mostly from the Pediatric Eye Disease Investigator Group, has validated both number of hours a day of patching and days per week of atropine use. The use of glasses alone has also been established as a good first-line therapy for both anisometropic and strabismic amblyopia. Unfortunately, visual acuity equalisation or even improvement is not always attainable with these methods. Additionally, non-compliance with prescribed therapies contributes to treatment failures, with data supporting difficulty adhering to full treatment sessions. Interest in alternative therapies for amblyopia treatment has long been a topic of interest among researchers and clinicians alike. Incorporating new technology with an understanding of the biological basis of amblyopia has led to enthusiasm for binocular treatment of amblyopia. Early work on perceptual learning as well as more recent enthusiasm for iPad-based dichoptic training have each generated interesting and promising data for vision improvement in amblyopes. Use of pharmaceutical augmentation of traditional therapies has also been investigated. Several different drugs with unique mechanisms of action are thought to be able to neurosensitise the brain and enhance responsiveness to amblyopia therapy. No new treatment has emerged from currently available evidence as superior to the traditional therapies in common practice today. But ongoing investigation into the use of both new technology and the understanding of the neural basis of amblyopia promises alternate or perhaps better cures in the future.

Effects of the Tyrosinase-Dependent Dopaminergic System on Refractive Error Development in Guinea Pigs

Purpose

To determine if myopia in albino guinea pigs is linked to altered ocular dopamine (DA) levels in both the retinal and uveal dopaminergic systems.

Methods

Retina and retinal pigment epithelium (RPE)/choroid were dissected from eyes of 2-week-old albino myopic (AM) and pigmented hyperopic (PH) guinea pigs. The levels of DA, dihydroxy-phenyl acetic acid (DOPAC), and homovanillic acid (HVA) were determined. Tyrosine hydroxylase (TH) and tyrosinase activities were also measured. PH animals received daily unilateral peribulbar injections of either kojic acid (tyrosinase inhibitor) or vehicle for 2 to 4 weeks. Refractive errors and ocular axial dimensions were measured by eccentric infrared photoretinoscopy and A-scan ultrasonography.

Results

Retinal DA levels were similar between the two strains, but AM eyes had higher levels of DOPAC. RPE/choroid DA and tyrosinase activity in AM eyes were lower than in PH eyes (P < 0.01); however, the DA turnover was higher (P < 0.05). After 2 weeks of kojic acid treatment, PH eyes developed significant myopia, accompanied by elongated vitreous chambers and axial lengths. Inhibition of tyrosinase activity was linearly correlated with a myopic refraction shift (R = 0.79, P < 0.01). PH animals that received 62.5 ng/mL kojic acid treatment daily for 2 weeks followed by 625 ng/mL for 2 more weeks became more myopic and had deeper anterior chambers compared to those that received the 62.5 ng/mL dose over this period (P = 0.04).

Conclusions

The uveal tyrosinase-dependent dopaminergic system is involved in the development of guinea pig refraction. Enhancing uveal tyrosinase activity might slow down the development of myopia.

Circadian rhythms, refractive development, and myopia

PURPOSE

Despite extensive research, mechanisms regulating postnatal eye growth and those responsible for ametropias are poorly understood. With the marked recent increases in myopia prevalence, robust and biologically-based clinical therapies to normalize refractive development in childhood are needed. Here, we review classic and contemporary literature about how circadian biology might provide clues to develop a framework to improve the understanding of myopia etiology, and possibly lead to rational approaches to ameliorate refractive errors developing in children.

RECENT FINDINGS

Increasing evidence implicates diurnal and circadian rhythms in eye growth and refractive error development. In both humans and animals, ocular length and other anatomical and physiological features of the eye undergo diurnal oscillations. Systemically, such rhythms are primarily generated by the 'master clock' in the surpachiasmatic nucleus, which receives input from the intrinsically photosensitive retinal ganglion cells (ipRGCs) through the activation of the photopigment melanopsin. The retina also has an endogenous circadian clock. In laboratory animals developing experimental myopia, oscillations of ocular parameters are perturbed. Retinal signaling is now believed to influence refractive development; dopamine, an important neurotransmitter found in the retina, not only entrains intrinsic retinal rhythms to the light:dark cycle, but it also modulates refractive development. Circadian clocks comprise a transcription/translation feedback control mechanism utilizing so-called clock genes that have now been associated with experimental ametropias. Contemporary clinical research is also reviving ideas first proposed in the nineteenth century that light exposures might impact refraction in children. As a result, properties of ambient lighting are being investigated in refractive development. In other areas of medical science, circadian dysregulation is now thought to impact many non-ocular disorders, likely because the patterns of modern artificial lighting exert adverse physiological effects on circadian pacemakers. How, or if, such modern light exposures and circadian dysregulation contribute to refractive development is not known.

SUMMARY

The premise of this review is that circadian biology could be a productive area worthy of increased investigation, which might lead to the improved understanding of refractive development and improved therapeutic interventions.

Dopamine signaling and myopia development: What are the key challenges

In the face of an "epidemic" increase in myopia over the last decades and myopia prevalence predicted to reach 2.5 billion people by the end of this decade, there is an urgent need to develop effective and safe therapeutic interventions to slow down this "myopia booming" and prevent myopia-related complications and vision loss. Dopamine (DA) is an important neurotransmitter in the retina and mediates diverse functions including retina development, visual signaling, and refractive development. Inspired by the convergence of epidemiological and animal studies in support of the inverse relationship between outdoor activity and risk of developing myopia and by the close biological relationship between light exposure and dopamine release/signaling, we felt it is timely and important to critically review the role of DA in myopia development. This review will revisit several key points of evidence for and against DA mediating light control of myopia: 1) the causal role of extracellular retinal DA levels, 2) the mechanism and action of dopamine D1 and D2 receptors and 3) the roles of cellular/circuit retinal pathways. We examine the experiments that show causation by altering DA, DA receptors and visual pathways using pharmacological, transgenic, or visual environment approaches. Furthermore, we critically evaluate the safety issues of a DA-based treatment strategy and some approaches to address these issues. The review identifies the key questions and challenges in translating basic knowledge on DA signaling and myopia from animal studies into effective pharmacological treatments for myopia in children.

Amblyopia update: new treatments

PURPOSE OF REVIEW

This review article is an update on the current treatments for amblyopia. In particular, the authors focus on the concepts of brain plasticity and their implications for novel treatment strategies for both children and adults affected by amblyopia.

RECENT FINDINGS

A variety of strategies has been developed to treat amblyopia in children and adults. New evidence on the pathogenesis of amblyopia has been obtained both in animal models and in clinical trials. Mainly, these studies have challenged the classical concept that amblyopia becomes untreatable after the 'end' of the sensitive or critical period of visual development, because of a lack of sufficient plasticity in the adult brain.

SUMMARY

New treatments for amblyopia in children and adults are desirable and should be encouraged. However, further studies should be completed before such therapies are widely accepted into clinical practice.