An updated view on the role of dopamine in myopia

Genetic variants linked to myopic macular degeneration in persons with high myopia: CREAM Consortium

Purpose

To evaluate the roles of known myopia-associated genetic variants for development of myopic macular degeneration (MMD) in individuals with high myopia (HM), using case-control studies from the Consortium of Refractive Error and Myopia (CREAM).

Methods

A candidate gene approach tested 50 myopia-associated loci for association with HM and MMD, using meta-analyses of case-control studies comprising subjects of European and Asian ancestry aged 30 to 80 years from 10 studies. Fifty loci with the strongest associations with myopia were chosen from a previous published GWAS study. Highly myopic (spherical equivalent [SE] ≤ -5.0 diopters [D]) cases with MMD (N = 348), and two sets of controls were enrolled: (1) the first set included 16,275 emmetropes (SE ≤ -0.5 D); and (2) second set included 898 highly myopic subjects (SE ≤ -5.0 D) without MMD. MMD was classified based on the International photographic classification for pathologic myopia (META-PM).

Results

In the first analysis, comprising highly myopic cases with MMD (N = 348) versus emmetropic controls without MMD (N = 16,275), two SNPs were significantly associated with high myopia in adults with HM and MMD: (1) rs10824518 (P = 6.20E-07) in KCNMA1, which is highly expressed in human retinal and scleral tissues; and (2) rs524952 (P = 2.32E-16) near GJD2. In the second analysis, comprising highly myopic cases with MMD (N = 348) versus highly myopic controls without MMD (N = 898), none of the SNPs studied reached Bonferroni-corrected significance.

Conclusions

Of the 50 myopia-associated loci, we did not find any variant specifically associated with MMD, but the KCNMA1 and GJD2 loci were significantly associated with HM in highly myopic subjects with MMD, compared to emmetropes.

Zone of retinal vascularization and refractive error in premature eyes with and without spontaneously regressed retinopathy of prematurity

PURPOSE

To evaluate the relationship between zone of retinal vascularization and refractive error in premature infants without retinopathy of prematurity (ROP) or with spontaneously regressed ROP.

METHODS

The medical records of neonates screened for ROP between 2009 and 2015 at a tertiary academic center were reviewed retrospectively. Cases included untreated eyes with spontaneously regressed ROP; premature eyes without a diagnosis of ROP were control subjects. Primary outcomes were zone of retinal vascularization and refractive error, determined by cycloplegic retinoscopy (CR).

RESULTS

Of 378 eyes evaluated, 184 had ROP, 24 of which underwent treatment and were excluded. Mean corrected age at first CR was 7.5 months. Seventeen eyes without ROP were myopic at first CR (8.8%), compared to 35 eyes with regressed ROP (21.9%). No untreated eyes had halted vasculature in zone I; notably, 44% of spontaneously regressed zone II eyes were myopic. Irrespective of ROP status, CR significantly differed by zone of vascularization (P < 0.001), with more myopia occurring with posterior halting of vascularization. For all eyes, CR significantly differed between complete vascularization versus zone II (P < 0.0001) and zone III versus zone II (P = 0.001); zone III versus complete vascularization did not statistically differ (P = 0.15). This relationship held true for untreated, spontaneously regressed ROP eyes (P < 0.01, P = 0.01, P = 0.8343).

CONCLUSIONS

More myopic refraction occurred in neonates screened for ROP with posterior halting of vascularization. Patients with halted vascular growth in zone II should be closely monitored for myopia and refractive amblyopia.

Dose-Response Relationship of Outdoor Exposure and Myopia Indicators: A Systematic Review and Meta-Analysis of Various Research Methods

Myopia in children has dramatically increased worldwide. A systematic review and meta-analysis were conducted to evaluate the effects of outdoor light exposure on myopia. According to research data from 13 studies of 15,081 children aged 4-14 at baseline, outdoor light exposure significantly reduced myopia incidence/prevalence (odds ratio [OR] = 0.85, 95% confidence interval [CI]: 0.80-0.91, p < 0.00001; I2 = 90%), spherical equivalent refractive error (SER) by 0.15 D/year (0.09-0.27, p < 0.0001), and axial elongation by 0.08 mm/year (-0.14 to -0.02, p = 0.02). The benefits of outdoor light exposure intervention, according to pooled overall results, included decreases in three myopia indicators: 50% in myopia incidence, 32.9% in SER, and 24.9% in axial elongation for individuals in Asia. Daily outdoor light exposure of more than 120 min was the most effective intervention, and weekly intervention time exhibited a dose-response relationship with all three indicators. Subgroup comparisons revealed that interventional studies report greater benefits from outdoor light exposure compared with cohort and cross-sectional studies, and individuals with myopia in intervention studies experienced slightly greater benefits than individuals without, in terms of SER and axial elongation. Therefore, this study suggests 120 min/day of outdoor light exposure at school.

The Increasing Burden of Myopia in Israel among Young Adults over a Generation: Analysis of Predisposing Factors

PURPOSE

To determine the trends in prevalence of myopia in Israeli young adults over approximately a generation, as well as associated factors and variation in the impact of these factors on myopia prevalence in this region over time.

DESIGN

Retrospective, cross-sectional study.

PARTICIPANTS

One hundred four thousand six hundred eighty-nine consecutive persons 16 to 19 years of age born between 1971 and 1994 who had not yet enlisted in the Israeli Army but had completed the medical profiling process.

METHODS

Using data collected at a north Israel recruitment center, the prevalence of myopia over time was estimated, and a polynomial regression analysis was performed to assess significance of nonlinear trends. Associations of demographic and socioeconomic factors with myopia were assessed, and trends over time were analyzed using a factorial logistic regression.

MAIN OUTCOME MEASURES

The primary outcome measure was factors associated with the prevalence of myopia over time. The secondary outcome measure was a description of the change in prevalence of myopia over time.

RESULTS

The prevalence of myopia increased 1.284-fold over 24 years from 20.4% among participants born between 1971 and 1982 to 26.2% among participants born between 1983 and 1994. A quite similar increase was observed among males (from 17.9% to 22.7%, respectively) and females (from 23.9% to 30.8%, respectively). The factors found to be associated with myopia were as follows: more recent date of birth, female gender, more years of education, being the eldest child, non-Israeli ethnic origin, and urban residence. However, there were significant trends over time in the effects of some of these factors, most notably an attenuation of the difference between participants of different religions in the recent birth-years period. Most of these associations and trends were observed in both males and females separately, with some gender-specific variations. Immigrants from Ethiopia who were raised in Israel were highly more likely to demonstrate myopia than those who arrived at an older age.

CONCLUSIONS

This study demonstrated an increase in the prevalence of myopia and the possible associations of urbanization- and higher education-related factors among several subpopulations and the risk for myopia developing.

The Effect of Atropine on Human Global Flash mfERG Responses to Retinal Defocus

Purpose

To investigate the action of atropine on global flash multifocal electroretinogram (gmfERG) responses to retinal defocus.

Method

gmfERG recordings were made monocularly in 19 healthy adults under three lens-imposed defocus conditions (2 diopters myopic, 2 diopters hyperopic, and no defocus) before and 24 hours after instillation of 1 drop of 0.1% atropine. Signals reflecting activity from the outer and inner retina (direct [DC] and induced [IC] components respectively) were analyzed. Responses were grouped into either a central (0°-6°) or peripheral (6°-24°) retinal zone. The gmfERG responses were compared relative to the no defocus, no atropine condition.

Results

Within the central zone, atropine had no effect on the amplitudes and peak times of DC or IC responses to defocus. For IC responses in the peripheral zone, there was a significant interaction effect of atropine and defocus (F2,36 = 6.050, P = 0.011) with greater post-atropine amplitudes under myopic defocus (mean increase = 15.5%, 95% confidence interval [CI] = 5.6%-25.4%, P = 0.004). Atropine also had a significant main effect of increasing IC peak times (F1,18 = 9.722, P = 0.006). For DC responses, atropine had a significant main effect of increasing DC amplitudes (F1,18 = 7.821, P = 0.012) and peak times (F1,18 = 15.406, P = 0.001) regardless of sign of defocus.

Conclusions

Our results imply that atropine acts in the inner layers of the peripheral retina to affect neuronal responses to myopic defocus, raising the possibility that atropine may potentiate the effects of myopic defocus in inhibiting eye growth.

A Risk Score System for Myopia Symptom Warning

Myopia is the leading cause of visual impairments worldwide. Some studies revealed that visual experience in early life affected the final myopia, indicating that environmental factors play an impellent role in the development of myopia. However, risk factors of myopia are still not identified among adolescents in China. A total of 4104 cases of myopia symptom and 3306 emmetropia controls were selected from students in primary and middle schools in Wuhan in 2008. We identified the risk factors associated with myopia symptom by multivariate logistic regression in this cross-sectional study and constructed a risk score system for myopia symptom. The value of the area under the receiver operating characteristic curve (ROC) was 0.735. Furthermore, we followed up 93 students aged 7-9 years for one year and calculated the total points using the score system. We found no significant difference between the final myopia symptom and the results predicted by the total points by pair chi-square test (P>0.05). The score system had a modest ability to estimate the risk factors of myopia symptom. Using this score system, we could identify the students who are at risk of myopia symptom in the future according to their behaviors and environmental factors, and take measures to slow the progress of myopia symptom.

Altered ocular parameters from circadian clock gene disruptions

The pathophysiology of refractive errors is poorly understood. Myopia (nearsightedness) in particular both blurs vision and predisposes the eye to many blinding diseases during adulthood. Based on past findings of diurnal variations in the dimensions of the eyes of humans and other vertebrates, altered diurnal rhythms of these ocular dimensions with experimentally induced myopia, and evolving evidence that ambient light exposures influence refractive development, we assessed whether disturbances in circadian signals might alter the refractive development of the eye. In mice, retinal-specific knockout of the clock gene Bmal1 induces myopia and elongates the vitreous chamber, the optical compartment separating the lens and the retina. These alterations simulate common ocular findings in clinical myopia. In Drosophila melanogaster, knockouts of the clock genes cycle or period lengthen the pseudocone, the optical component of the ommatidium that separates the facet lens from the photoreceptors. Disrupting circadian signaling thus alters optical development of the eye in widely separated species. We propose that mechanisms of myopia include circadian dysregulation, a frequent occurrence in modern societies where myopia also is both highly prevalent and increasing at alarming rates. Addressing circadian dysregulation may improve understanding of the pathogenesis of refractive errors and introduce novel therapeutic approaches to ameliorate myopia development in children.

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.

Divergence, evolution and adaptation in ray-finned fish genomes

With the rapid development of next-generation sequencing technologies and bioinformatics, over 50 ray-finned fish genomes by far have been sequenced with high quality. The genomic work provides abundant genetic resources for deep understanding of divergence, evolution and adaptation in the fish genomes. They are also instructive for identification of candidate genes for functional verification, molecular breeding, and development of novel marine drugs. As an example of other omics data, the Fish-T1K project generated a big database of fish transcriptomes to integrate with these published fish genomes for potential applications. In this review, we highlight the above-mentioned recent investigations and core topics on the ray-finned fish genome research, with a main goal to obtain a deeper understanding of fish biology for theoretical and practical applications.

Dim Light Exposure and Myopia in Children

Purpose

Experimental myopia in animal models suggests that bright light can influence refractive error and prevent myopia. Additionally, animal research indicates activation of rod pathways and circadian rhythms may influence eye growth. In children, objective measures of personal light exposure, recorded by wearable light sensors, have been used to examine the effects of bright light exposure on myopia. The effect of time spent in a broad range of light intensities on childhood refractive development is not known. This study aims to evaluate dim light exposure in myopia.

Methods

We reanalyzed previously published data to investigate differences in dim light exposure across myopic and nonmyopic children from the Role of Outdoor Activity in Myopia (ROAM) study in Queensland, Australia. The amount of time children spent in scotopic (<1-1 lux), mesopic (1-30 lux), indoor photopic (>30-1000 lux), and outdoor photopic (>1000 lux) light over both weekdays and weekends was measured with wearable light sensors.

Results

We found significant differences in average daily light exposure between myopic and nonmyopic children. On weekends, myopic children received significantly less scotopic light (P = 0.024) and less outdoor photopic light than nonmyopic children (P < 0.001). In myopic children, more myopic refractive errors were correlated with increased time in mesopic light (R = -0.46, P = 0.002).

Conclusions

These findings suggest that in addition to bright light exposure, rod pathways stimulated by dim light exposure could be important to human myopia development. Optimal strategies for preventing myopia with environmental light may include both dim and bright light exposure.

Amphiregulin and ocular axial length

PURPOSE

To assess the potential role of amphiregulin as messenger molecule in ocular axial elongation.

METHODS

The experimental study included guinea pigs (total n = 78) (age: 3-4 weeks) which underwent bilateral lens-induced myopization and received 15 days later three intraocular injections in weekly intervals of amphiregulin antibody (doses:5 μg, 10 μg, 20 μg) into their right eyes, and three phosphate-buffered saline injections into their left eyes; and guinea pigs without lens-induced myopization and which received three unilateral intraocular injections of amphiregulin antibody (dose: 20 μg) or amphiregulin (doses: 1 ng; 10 ng; 20 ng) into their right eyes, and three phosphate-buffered saline injections into their left eyes. Seven days later, the animals were sacrificed. Intravitally, we performed biometry, and histology and immunohistochemistry post-mortem.

RESULTS

In animals with bilateral lens-induced myopization, the right eyes receiving amphiregulin antibody showed reduced axial elongation in a dose-dependent manner (dose: 5 μg: side difference: 0.14 ± 0.05 mm;10 μg: 0.22 ± 0.06 mm; 20 μg: 0.32 ± 0.06 mm; p < 0.001), thicker sclera (all p < 0.05) and higher cell density in the retinal nuclear layers and retinal pigment epithelium (RPE) (all p < 0.05). In animals without lens-induced myopia, the right eyes with amphiregulin antibody application (20 μg) showed reduced axial elongation (p = 0.04), and the right eyes with amphiregulin injections experienced increased (p = 0.02) axial elongation in a dose-dependent manner (1 ng: 0.04 ± 0.06 mm; 10 ng: 0.10 ± 0.05 mm; 20 ng: 0.11 ± 0.06 mm). Eyes with lens-induced axial elongation as compared to eyes without lens-induced axial elongation revealed an increased visualization of amphiregulin upon immunohistochemistry and higher expression of mRNA of endogenous amphiregulin and epidermal growth factor receptor, in particular in the outer part of the retinal inner nuclear layer and in the RPE.

CONCLUSION

Amphiregulin may be associated with axial elongation in young guinea pigs.

Dopamine levels in human tear fluid

Purpose

To determine the levels of dopamine in tear fluid and demonstrate the use of tear fluid as a non-invasive source for dopamine measurements in humans.

Methods

The study cohort included 30 clinically healthy individuals without any pre-existing ocular or systemic conditions. Matched tear fluid (using Schirmer's strips and capillary tubes) and plasma were collected from the subjects. Dopamine levels were evaluated using direct competitive chemiluminescent enzyme-linked immunosorbent assay (ELISA), dopamine kit (Cloud Clone Corp, TX, USA).

Results

Significantly higher dopamine levels were found in the tear fluid compared to plasma in the study subjects. The level of dopamine was 97.2 ± 11.80 pg/ml (mean ± SEM), 279 ± 14.8 pg/ml (mean ± SEM), and 470.4 ± 37.64 pg/ml (mean ± SEM) in the plasma and in the tears collected using Schirmer's strips and capillary tubes, respectively.

Conclusion

Dopamine was detectable in all the tear fluid samples tested and was also found to be at a higher concentration than in plasma samples. Tear fluid can be used as a non-invasive sample source to monitor dopamine levels.

Visual Acuity in Late Adolescence and Future Psychosis Risk in a Cohort of 1 Million Men

BACKGROUND

We aimed to determine whether late adolescent visual impairment is associated with later psychosis.

METHODS

We conducted a longitudinal cohort study of Swedish male military conscripts aged 18 or 19 years from January 1, 1974, through December 31, 1997 (N = 1140710). At conscription, uncorrected and optometry-lens-corrected distance visual acuity was measured. Participants were then followed up to see if they received an inpatient diagnosis of non-affective psychotic disorder, including schizophrenia (N = 10769). Multivariable Cox modeling was used to estimate differences between groups.

RESULTS

After adjustment for confounders, those with severe impairment before optical correction in their best eye (decimal fraction <0.3) had an increased psychosis rate compared to those with normal uncorrected vision (decimal fraction 1.0) (hazard ratio [HR] 1.26, 95% CI 1.16-1.37). Larger interocular visual acuity difference was associated with an increased psychosis rate (adjusted HR 1.49, 95% CI 1.37-1.63 in those with differences >0.5 compared to those with no between eye acuity difference). Individuals with impaired vision that could not be corrected to normal with lenses had highest rates of psychosis (best eye adjusted HR 1.56; 95% CI 1.33-1.82), those with imperfect, but correctable vision also had elevated rates (best eye adjusted HR 1.21; 95% CI 1.15-1.28). Individuals with visual impairment had higher rates of psychosis than their full siblings with normal vision (adjusted HR 1.20, 95% CI 1.07-1.35).

CONCLUSIONS

Impaired visual acuity is associated with non-affective psychosis. Visual impairment as a phenotype in psychosis requires further consideration.

Changes in fundus reflectivity during myopia development in chickens

Previous studies have shown that changes in functional activity in the retina can be visualized as changes in fundus reflectivity. When the image projected on the retina is low pass filtered or defocused by covering the eye with a frosted diffuser or a negative lens, it starts growing longer and develops myopia. We have tested the hypothesis that the resulting altered retinal activity may show up as changes in fundus reflectivity. Fundus reflectivity was measured in chickens in vivo, both in visible (400-800 nm, white) and near ultraviolet (UV) light (315-380 nm). Two CCD cameras were used; a RGB camera and a camera sensitive in near UV light (peak sensitivity at 360 nm). White and UV LEDs, respectively, placed in the center of the camera lens aperture, served as light sources. Software was written to flash the LEDs and record the average brightness of the pupil that was illuminated by light reflected from the fundus. The average pixel grey level (px) in the pupil was taken as a measure of the amount of reflected light while refractive errors were corrected by trial lenses after pupil brightness was corrected for pupil size. It was found that myopic eyes had brighter pupils in UV light, compared to eyes with normal vision, no matter whether myopia was induced by diffusers or negative lenses (48 ± 9 vs. 28 ± 3, p<0.001 and 47 ± 7 vs. 27 ± 2, respectively). Using SD-OCT in alert chickens it was found that the retinal nerve fiber layer (RNFL) and the retinal ganglion cell layer (RGCL) in the central retina became thinner already at early stages of myopia development, compared to controls (31.2 ± 5.8 µm vs. 43.9 ± 2.6 µm, p<0.001 and 36.9 ± 1.2 µm vs. 44 ± 0.5 µm, respectively). While the decrease in RNFL thickness occurred concomitantly with the increase in UV reflectivity, it remains unclear whether these changes were causally linked. Thinning of the RNFL could be due to reduced neural activity in retinal ganglion cells but also due to metabolic changes in the retina during myopia development.

The Interactions Between Bright Light and Competing Defocus During Emmetropization in Chicks

Purpose

The environment comprises multiple optical signals that affect eye growth. We aimed to determine if the inhibitory effects of myopic defocus and bright light (BL) against myopia are additive in the presence of the myopia-genic hyperopic defocus.

Methods

In experiment 1, three groups of 24 chicks each were fitted with the following multizone dual-power lenses (pl): pl/-10 D (50:50 area), +10/-10 D (50:50 area), and +10/-10 D (33:67 area) monocularly for 6 days. Half of each group were raised under normal illumination of 500 lux, 12/12-hour light/dark cycle, whereas the remainder were exposed to 6-hour BL of 40 klx and 6-hour 500 lux during the light cycle. In experiment 2, 38 chicks wore +10/-10 D (33:67 area) lenses monocularly for 8 days and were exposed to one of four light intensities for 6 hours per day-500 lux, 10 klx, 20 klx, or 40 klx-and received 500 lux for the remainder of the light cycle.

Results

In experiment 1, interocular difference in refractions after 6 days for the three groups were -3.6 D, +2.0 D, and -4.2 D, respectively, under normal light and were -0.9 D, +4.2 D, and +0.67 D under BL, manifesting as a shorter anterior segment and vitreous chamber. In experiment 2, the effect of BL increased with light intensity in the +10/-10 D (33:67) group, with a significant difference in refraction between the 10 klx and 20 klx groups (interocular difference -2.75 ± 2.76 D vs. 1.70 ± 2.40 D, P < 0.01), but plateaued between 20 klx and 40 klx (1.70 ± 2.40 D vs. 1.70 ± 0.35 D, P > 0.05).

Conclusions

The protective effects of myopic defocus and BL against experimental myopia were additive. The inhibitory effect of BL against myopia was dose dependent at 10 klx and above but plateaued at 20 klx.

Myopia-Inhibiting Concentrations of Muscarinic Receptor Antagonists Block Activation of Alpha2A-Adrenoceptors In Vitro

Purpose

Myopia is a refractive disorder that degrades vision. It can be treated with atropine, a muscarinic acetylcholine receptor (mAChR) antagonist, but the mechanism is unknown. Atropine may block α-adrenoceptors at concentrations ≥0.1 mM, and another potent myopia-inhibiting ligand, mamba toxin-3 (MT3), binds equally well to human mAChR M4 and α1A- and α2A-adrenoceptors. We hypothesized that mAChR antagonists could inhibit myopia via α2A-adrenoceptors, rather than mAChR M4.

Methods

Human mAChR M4 (M4), chicken mAChR M4 (cM4), or human α2A-adrenergic receptor (hADRA2A) clones were cotransfected with CRE/promoter-luciferase (CRE-Luc; agonist-induced luminescence) and Renilla luciferase (RLuc; normalizing control) into human cells. Inhibition of normalized agonist-induced luminescence by antagonists (ATR: atropine; MT3; HIM: himbacine; PRZ: pirenzepine; TRP: tropicamide; OXY: oxyphenonium; QNB: 3-quinuclidinyl benzilate; DIC: dicyclomine; MEP: mepenzolate) was measured using the Dual-Glo Luciferase Assay System.

Results

Relative inhibitory potencies of mAChR antagonists at mAChR M4/cM4, from most to least potent, were QNB > OXY ≥ ATR > MEP > HIM > DIC > PRZ > TRP. MT3 was 56× less potent at cM4 than at M4. Relative potencies of mAChR antagonists at hADRA2A, from most to least potent, were MT3 > HIM > ATR > OXY > PRZ > TRP > QNB > MEP; DIC did not antagonize.

Conclusions

Muscarinic antagonists block hADRA2A signaling at concentrations comparable to those used to inhibit chick myopia (≥0.1 mM) in vivo. Relative potencies at hADRA2A, but not M4/cM4, correlate with reported abilities to inhibit chick form-deprivation myopia. mAChR antagonists might inhibit myopia via α2-adrenoceptors, instead of through the mAChR M4/cM4 receptor subtype.

Study of Vesicular Monoamine Transporter 2 in Myopic Retina Using [18F]FP-(+)-DTBZ

PURPOSE

To investigate the relationship between expression level of vesicular monoamine transporter 2 (VMAT2) and myopia, as well as the feasibility of noninvasive myopia diagnosis through imaging VMAT2 in retina by using [¹⁸F]fluoropropyl-(+)-dihydrotetrabenazine ([¹⁸F]FP-(+)-DTBZ).

PROCEDURES

The right eyes of ten guinea pigs were deprived of vision to establish form-deprived (FD) myopia and the left eyes were untreated as the self-control eyes. The location and expression level of VMAT2 in the eyes were detected by micro-positron emission tomography (PET)/X-ray computed tomography (CT) imaging through using [¹⁸F]FP-(+)-DTBZ. Immunofluorescence staining and Western blot were used to confirm the location and expression level of VMAT2 in the eyes. The concentrations of dopamine (DA) and its metabolites including 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were also investigated by high-performance liquid chromatography.

RESULTS

The right eyes deprived of vision were obviously myopic (- 3.17 ± 1.33 D) after procedure, while the left eyes were hyperopic (4.60 ± 0.83 D, P < 0.0001). The main expressions of VMAT2 in the eyes were located in retina. VMAT2 was significantly reduced in the myopic retina compared to the normal one from PET/CT results (P = 0.0008), which could also be verified by Western blots (P = 0.029). The concentrations of DA, DOPAC, and HVA in the FD eyes were all significantly less than those in the control eyes (P = 0.024, P = 0.018, P = 0.008). As a role of storing and releasing DA in vesicles, VMAT2 was demonstrated positively correlating with the amounts of DA (P = 0.030), DOPAC (P = 0.038), and HVA (P = 0.025) through Pearson's correlation coefficient test.

CONCLUSIONS

We demonstrate that [¹⁸F]FP-(+)-DTBZ can be used to noninvasively image VMAT2 in retina. The expression level of VMAT2 in retina may act as a new biomarker for myopia diagnosis. The decreasing of VMAT2 expression level may play an important role in the development of myopia through correspondingly reducing the amount of DA in retina.

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.

Alpha2 -adrenoceptor agonists inhibit form-deprivation myopia in the chick

BACKGROUND

The putative myopia-controlling receptor is thought to be muscarinic acetylcholine receptor subtype M₄ , because mamba toxin-3 can inhibit form-deprivation myopia in chicks at a far lower concentration than atropine. However, mamba toxin-3 is equally potent at the human α_1A -, α_1D -, and α_2A -adrenoceptors. To test the hypothesis that α-adrenoceptors might be involved in regulation of eye growth, the treatment effects of α₂ -adrenoceptor agonists brimonidine, clonidine, and guanfacine, and antagonist yohimbine, on form-deprivation myopia in the chick were measured.

METHODS

Right eyes of White Leghorn chicks were goggled with diffusers to induce form-deprivation myopia; left eyes were left open as controls. Goggled eyes were injected intravitreally with 20 μL of vehicle, or 2, 20, or 200 nmol of brimonidine, clonidine, guanfacine, or yohimbine, 24, 72, and 120 hours after goggle application. Alternatively, myopia was inhibited physiologically by goggle removal for two hours, and the α₂ -adrenoceptor antagonist, yohimbine, was injected to test whether it could block this type of myopia inhibition. One day after the last injection, refractive error and axial length were measured.

RESULTS

Brimonidine (20 and 200 nmol) and clonidine (200 nmol) effectively inhibited experimentally induced increases in negative refractive error and axial elongation. All doses of guanfacine significantly inhibited induced negative refractive error, but only 20 and 200 nmol significantly inhibited axial elongation. Yohimbine had no effect on form-deprivation myopia, but 200 nmol reduced the myopia-inhibiting effect of goggle removal.

CONCLUSION

High concentrations of α₂ -adrenoceptor agonists, similar to those required by atropine, inhibited chick form-deprivation myopia; antagonism by yohimbine had no effect. High-concentration yohimbine partially interfered with emmetropisation in form-deprived chicks experiencing normal vision for two hours per day. These data support the hypothesis that treatment with high concentrations of adrenergic drugs can affect experimentally induced myopia and normal visual processes.

Little effect of 0.01% atropine eye drops as used in myopia prevention on the pattern electroretinogram

PURPOSE

Daily administration of 0.01% atropine eye drops is a promising approach for myopia control. The mechanism of action is believed to involve the dopaminergic system of the retina, triggering an increased release of dopamine. Previous studies in psychiatric condition such as major depression suggest that pattern electroretinogram (PERG) amplitudes are modulated by changes in retinal dopamine. It is thus plausible that atropine eye drops could have an effect on PERG amplitudes. The present study was designed to test this, assessing the difference in amplitude between contrast levels and the ratio of amplitudes between check sizes as primary endpoints.

METHODS

We included 14 participants with no more than ± 2 diopters of ametropia and visual acuity of at least 1.0. One eye was chosen randomly in each participant for atropine application (14 days, one drop of 0.01% atropine solution once daily before bedtime). We recorded two sets of steady-state PERG recordings: one with different contrasts (25% and 98%) and one with different check sizes (0.8° and 17°). Near-point distance, near visual acuity, and pupil diameter were measured additionally.

RESULTS

The recordings to different contrasts did not show atropine-related changes of PERG amplitude. A small increase by 6% of the amplitude difference between contrast levels with atropine application was not significant (p = 0.08). Raw amplitudes in the check size condition increased with atropine by 17% (p < 0.01) and 10% (p < 0.03) for small and large checks, respectively, without a significant concomitant effect on the amplitude ratio. Pupil size was significantly affected (median increase 0.5 mm, p < 0.002). However, neither of the experimental conditions was associated with a significant correlation between pupil size and PERG effects.

CONCLUSION

The effects on PERG primary endpoints after the 14-day period of atropine administration were small, especially compared to effect sizes in major depression, and statistically insignificant. Effects on raw amplitude were inconsistent. The present results suggest that retinal processing as reflected by PERG does not sizably change following a treatment regimen with atropine that is typical for myopia control.

Genome-wide DNA hypermethylation and homocysteine increase a risk for myopia

AIM

To test for the association between genome-wide methylation and myopia in human and mice.

METHODS

Long interspersed nucleotide element 1 (LINE-1) methylation levels were used to surrogate genome-wide methylation level. We first tested for the association between high myopia (<-6 D) and LINE-1 methylation in leukocytes in 220 cases and 220 control subjects. Secondly, we validated the results of LINE-1 methylation in eyes from the form deprivation myopia (FDM) mice. Furthermore, we calculated the correlation of LINE-1 methylation levels between leukocyte DNA and ocular DNA in the mice. We also tested whether dopamine can alter LINE-1 methylation levels.

RESULTS

The LINE-1 methylation level was significantly higher in the myopic human subjects than controls. The upper and middle tertiles of the methylation levels increased an approximately 2-fold (P≤0.002) risk for myopia than the lower tertile. Similarly, FDM mice had high LINE-1 methylation levels in the leukocyte, retina and sclera, and furthermore the methylation levels detected from these three tissues were significantly correlated. Immunohistochemical staining revealed higher levels of homocysteine and methionine in the rodent myopic eyes than normal eyes. Dopamine treatment to the cells reduced both LINE-1 methylation and DNA methyltransferase levels.

CONCLUSION

LINE-1 hypermethylation may be associated with high myopia in human and mice. Homocysteine and methionine are accumulated in myopic eyes, which may provide excess methyl group for genome-wide methylation.

Effects of time-of-day on inhibition of lens-induced myopia by quinpirole, pirenzepine and atropine in chicks

Injections of the D2 dopamine receptor agonist quinpirole or the acetylcholine muscarinic receptor antagonists pirenzepine and atropine prevent the development of negative-lens-induced myopia in chicks by inhibiting ocular growth. Because ocular growth is diurnally rhythmic, we hypothesized that the efficacy for inhibition may depend on time of day. Chicks wore monocular -10D lenses for 5 days, starting at 12d of age. The light cycle was 12L/12D. The lens-wearing eye received daily intravitreal injections for 4 days, of 20 μl quinpirole (10 nmol), at the following times: 7:30 EST (lights-on; morning; n = 12), 12:00 (mid-day; n = 13), or 19:30 (evening; n = 17). The same protocol was used for pirenzepine (0.2 μmol) and atropine (18 nmol), at the following times: 8:30 EDT (lights-on; n = 10; n = 18), 14:00 (n = 10; n = 12), or 20:30 (n = 18; n = 16). Saline injections were done in separate groups of birds for all groups as controls, and the data combined (n = 28). Ocular dimensions were measured using A-scan ultrasonography on treatment day 1 at 12:00, and again on day 5 at 12:00; growth rate is defined as the change in axial length over 96 h. For quinpirole and pirenzepine, subsets (n's in Methods) of mid-day and evening groups were measured at 6 h intervals on day 5 (from 12:00 to 12:00) to obtain rhythm parameters for axial length and choroidal thickness; for atropine, only the mid-day group was measured. Refractions were measured on day 5 with a Hartinger's refractometer. For quinpirole and pirenzepine, mid-day injections were more effective at inhibiting ocular growth than evening (Exp-fellow: quinpirole: -68 vs 118 μm/96h; post-hoc Bonferroni p = 0.016; pirenzepine: 79 vs 215 μm/96h; p = 0.046). There were no between-group statistically significant differences for atropine. For quinpirole, the mid-day amplitude of the axial rhythm was smaller than for evening (95 vs 142 μm; p < 0.05), but there were no time-dependent effects on the rhythms for pirenzepine. For atropine, the amplitude of the axial-length rhythm was significantly larger than that for pirenzepine at mid-day. We conclude that there is a phase-dependent efficacy for quinpirole and pirenzepine, with mid-day injections being most effective. There were no consistent time-dependent alterations in rhythm parameters for any of the drugs.

Immunotoxin-Induced Ablation of the Intrinsically Photosensitive Retinal Ganglion Cells in Rhesus Monkeys

Purpose: Intrinsically photosensitive retinal ganglion cells (ipRGCs) contain the photopigment melanopsin, and are primarily involved in non-image forming functions, such as the pupillary light reflex and circadian rhythm entrainment. The goal of this study was to develop and validate a targeted ipRGC immunotoxin to ultimately examine the role of ipRGCs in macaque monkeys.

Methods: An immunotoxin for the macaque melanopsin gene (OPN4), consisting of a saporin-conjugated antibody directed at the N-terminus, was prepared in solutions of 0.316, 1, 3.16, 10, and 50 μg in vehicle, and delivered intravitreally to the right eye of six rhesus monkeys, respectively. Left eyes were injected with vehicle only. The pupillary light reflex (PLR), the ipRGC-driven post illumination pupil response (PIPR), and electroretinograms (ERGs) were recorded before and after injection. For pupil measurements, 1 and 5 s pulses of light were presented to the dilated right eye while the left pupil was imaged. Stimulation included 651 nm (133 cd/m²), and 4 intensities of 456 nm (16–500 cd/m²) light. Maximum pupil constriction and the 6 s PIPR were calculated. Retinal imaging was performed with optical coherence tomography (OCT), and eyes underwent OPN4 immunohistochemistry to evaluate immunotoxin specificity and ipRGC loss.

Results: Before injection, animals showed robust pupil responses to 1 and 5 s blue light. After injection, baseline pupil size increased 12 ± 17%, maximum pupil constriction decreased, and the PIPR, a marker of ipRGC activity, was eliminated in all but the lowest immunotoxin concentration. For the highest concentrations, some inflammation and structural changes were observed with OCT, while eyes injected with lower concentrations appeared normal. ERG responses showed better preserved retinal function with lower concentrations. Immunohistochemistry showed 80–100% ipRGC elimination with the higher doses being more effective; however this could be partly due to inflammation that occurred at the higher concentrations.

Conclusion: Findings demonstrated that the OPN4 macaque immunotoxin was specific for ipRGCs, and induced a graded reduction in the PLR, as well as, in ipRGC-driven pupil response with concentration. Further investigation of the effects of ipRGC ablation on ocular and systemic circadian rhythms and the pupil in rhesus monkeys will provide a better understanding of the role of ipRGCs in primates.

TEMPORAL VASCULAR ARCADE WIDTH AND ANGLE IN HIGH AXIAL MYOPIA

PURPOSE

Axial myopia is associated with elongation of the posterior ocular segment. The authors measured posterior fundus landmarks and assessed their associations with axial length.

METHODS

Using fundus photographs, the authors measured the vertical distance between the temporal superior and temporal inferior arterial arcade (VDA) and the angle kappa between the temporal arterial arcades among other morphometric variables.

RESULTS

The study included 456 eyes with a mean age of 61.2 ± 14.2 years (range: 13-88 years) and mean axial length of 29.4 ± 2.1 mm (range: 23.2-35.3 mm). Mean angle kappa was 91.3 ± 17.2° (range: 39-161°), and mean VDA was 7.93 ± 1.71 mm (range: 2.72-12.85 mm). In multivariate regression analysis, wider angle kappa was associated (regression coefficient r: 0.47) with shorter axial length (P = 0.002; beta: -0.17; B: -1.37; 95% confidence interval [CI]:-2.23 to -0.51), longer VDA (P < 0.001; beta: 0.27; B: 2.70; 95% CI: 1.85-3.54), shorter disk-foveola distance (P < 0.001; beta: -0.22; B: -4.76; 95% CI: -7.05 to -2.46), shorter vertical optic disk diameter (P = 0.002; beta: -0.14; B: -6.83; 95% CI: -11.1 to -2.56), lower number of any chorioretinal lesions (P = 0.007; beta: -0.13; B: -2.11; 95% CI: -3.63 to -0.58), and longer maximal vertical chorioretinal lesion diameter (P = 0.05; beta: 0.09; B: 0.92; 95% CI: -0.02 to 1.86). A longer VDA was associated (r: 0.31) with longer axial length (P < 0.001; beta: 0.22; B: 0.18; 95% CI: 0.10-0.25), wider angle kappa (P < 0.001; beta: 0.28; B: 0.03; 95% CI: 0.02-0.04) and higher number of chorioretinal lesions (P = 0.03; beta: 0.10; B: 0.16; 95% CI: 0.02-0.31). If eyes with chorioretinal lesions were excluded, the association between longer VDA and longer axial length was no longer statistically significant (P > 0.10).

CONCLUSION

Axial elongation was correlated with decreasing angle kappa, caused by an elongation of the disk-foveola distance because of an enlargement of the gamma zone, whereas VDA remained constant. By contrast, horizontal length of macular Bruch membrane and vertical length of macular Bruch membrane were independent of axial elongation. Axial elongation did not lead to lengthening of Bruch membrane in the macular region in eyes without macular chorioretinal lesions.

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.

[Atropine use for the prevention of myopia progression]

Given the prevalence of myopic refraction (from 50 to 84% in Asian countries and 35 to 49% in European countries and the United States in young people), the development of methods for monitoring and preventing myopia continues to be an urgent task. One of the directions of pharmacological intervention on the progression of myopia is associated with the use of a non-selective M-cholinoreceptors antagonist - atropine. The review presents the results of studies on various aspects of the potential for topical application of atropine to control the progression of myopia (experimental and clinical data on the mechanism of action, the effectiveness of clinical use, the possible side effects of various concentrations of the drug).The heterogeneity of the data presented does not yet lead to the conclusion that the long-term instillations of atropine are effective in prevention of progressive myopia. In addition, the wide application of this method, for example, in the territory of the Russian Federation, is limited by approved official instruction for the local application of the atropine solution in ophthalmology.

Epigenetic dysregulation of host gene expression in Toxoplasma infection with specific reference to dopamine and amyloid pathways

Recent interest has focussed on the influence of infectious disease organisms on the host epigenome. Toxoplasma gondii infection acquired congenitally or in early life is associated with severe ocular and brain developmental anomalies, while persistent asymptomatic infection is a proposed risk factor for neurodegenerative and psychiatric disorders, including Parkinson's and Alzheimer's Diseases, and schizophrenia. Genome-wide analysis of the host methylome and transcriptome following T. gondii infection in a retinal cell line identified genes (132, 186 and 128 genes at 2, 6 and 24 h post-infection) concordant for methylation and expression, i.e. hypermethylated and decreased expression or hypomethylated and increased expression. Pathway analyses showed perturbation of two neurologically-associated pathways: dopamine-DARPP32 feedback in cAMP signalling (p-value = 8.3 × 10^-5; adjusted p-value = 0.020); and amyloid processing (p-value = 1.0 × 10^-3; adjusted p-value = 0.043). Amyloid Precursor Protein (APP) decreased in level following T. gondii infection. These results are of interest given the expression of APP early in nervous system development affecting neural migration and the role of amyloid processing in Alzheimer's disease, while dopamine has roles in the developing retina as well as in Parkinson's disease and schizophrenia. Our results provide a possible functional link between T. gondii infection and congenital/early life and adult neurological clinical signs.

Reading and Myopia: Contrast Polarity Matters

In myopia the eye grows too long, generating poorly focused retinal images when people try to look at a distance. Myopia is tightly linked to the educational status and is on the rise worldwide. It is still not clear which kind of visual experience stimulates eye growth in children and students when they study. We propose a new and perhaps unexpected reason. Work in animal models has shown that selective activation of ON or OFF pathways has also selective effects on eye growth. This is likely to be true also in humans. Using custom-developed software to process video frames of the visual environment in realtime we quantified relative ON and OFF stimulus strengths. We found that ON and OFF inputs were largely balanced in natural environments. However, black text on white paper heavily overstimulated retinal OFF pathways. Conversely, white text on black paper overstimulated ON pathways. Using optical coherence tomography (OCT) in young human subjects, we found that the choroid, the heavily perfused layer behind the retina in the eye, becomes about 16 µm thinner in only one hour when subjects read black text on white background but about 10 µm thicker when they read white text from black background. Studies both in animal models and in humans have shown that thinner choroids are associated with myopia development and thicker choroids with myopia inhibition. Therefore, reading white text from a black screen or tablet may be a way to inhibit myopia, while conventional black text on white background may stimulate myopia.

A Review of Current Concepts of the Etiology and Treatment of Myopia

Myopia occurs in more than 50% of the population in many industrialized countries and is expected to increase; complications associated with axial elongation from myopia are the sixth leading cause of blindness. Thus, understanding its etiology, epidemiology, and the results of various treatment regiments may modify current care and result in a reduction in morbidity from progressive myopia. This rapid increase cannot be explained by genetics alone. Current animal and human research demonstrates that myopia development is a result of the interplay between genetic and the environmental factors. The prevalence of myopia is higher in individuals whose both parents are myopic, suggesting that genetic factors are clearly involved in myopia development. At the same time, population studies suggest that development of myopia is associated with education and the amount time spent doing near work; hence, activities increase the exposure to optical blur. Recently, there has been an increase in efforts to slow the progression of myopia because of its relationship to the development of serious pathological conditions such as macular degeneration, retinal detachments, glaucoma, and cataracts. We reviewed meta-analysis and other of current treatments that include: atropine, progressive addition spectacle lenses, orthokeratology, and multifocal contact lenses.

Update in myopia and treatment strategy of atropine use in myopia control

The prevalence of myopia is increasing globally. Complications of myopia are associated with huge economic and social costs. It is believed that high myopia in adulthood can be traced back to school age onset myopia. Therefore, it is crucial and urgent to implement effective measures of myopia control, which may include preventing myopia onset as well as retarding myopia progression in school age children. The mechanism of myopia is still poorly understood. There are some evidences to suggest excessive expansion of Bruch’s membrane, possibly in response to peripheral hyperopic defocus, and it may be one of the mechanisms leading to the uncontrolled axial elongation of the globe. Atropine is currently the most effective therapy for myopia control. Recent clinical trials demonstrated low-dose atropine eye drops such as 0.01% resulted in retardation of myopia progression, with significantly less side effects compared to higher concentration preparation. However, there remain a proportion of patients who are poor responders, in whom the optimal management remains unclear. Proposed strategies include stepwise increase of atropine dosing, and a combination of low-dose atropine with increase outdoor time. This review will focus on the current understanding of epidemiology, pathophysiology in myopia and highlight recent clinical trials using atropine in the school-aged children, as well as the treatment strategy in clinical implementation in hyperopic, pre-myopic and myopic children.

Genome-wide association meta-analysis highlights light-induced signaling as a driver for refractive error

Refractive errors, including myopia, are the most frequent eye disorders worldwide and an increasingly common cause of blindness. This genome-wide association meta-analysis in 160,420 participants and replication in 95,505 participants increased the number of established independent signals from 37 to 161 and showed high genetic correlation between Europeans and Asians (>0.78). Expression experiments and comprehensive in silico analyses identified retinal cell physiology and light processing as prominent mechanisms, and also identified functional contributions to refractive-error development in all cell types of the neurosensory retina, retinal pigment epithelium, vascular endothelium and extracellular matrix. Newly identified genes implicate novel mechanisms such as rod-and-cone bipolar synaptic neurotransmission, anterior-segment morphology and angiogenesis. Thirty-one loci resided in or near regions transcribing small RNAs, thus suggesting a role for post-transcriptional regulation. Our results support the notion that refractive errors are caused by a light-dependent retina-to-sclera signaling cascade and delineate potential pathobiological molecular drivers.

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.

Mudskippers and Their Genetic Adaptations to an Amphibious Lifestyle

Mudskippers are the largest group of amphibious teleost fish that are uniquely adapted to live on mudflats. During their successful transition from aqueous life to terrestrial living, these fish have evolved morphological and physiological modifications of aerial vision and olfaction, higher ammonia tolerance, aerial respiration, improved immunological defense against terrestrial pathogens, and terrestrial locomotion using protruded pectoral fins. Comparative genomic and transcriptomic data have been accumulated and analyzed for understanding molecular mechanisms of the terrestrial adaptations. Our current review provides a general introduction to mudskippers and recent research advances of their genetic adaptations to the amphibious lifestyle, which will be helpful for understanding the evolutionary transition of vertebrates from water to land. Our insights into the genomes and transcriptomes will also support molecular breeding, functional identification, and natural compound screening.

A highly efficient murine model of experimental myopia

Despite the global pandemic of myopia, the precise molecular mechanism of the onset of myopia remains largely unknown. This is partially because of the lack of efficient murine myopic models that allow genetic manipulation at low cost. Here we report a highly practical and reproducible lens-induced myopia model by specially designed frames and lenses for mice. A lens power dependent myopic induction in mice was shown until minus 30 diopter lenses. The phenotype was significantly stronger than form-deprivation myopia. We presented the protocol for precise evaluations of the state of myopia, including refraction, corneal curvature and axial length using up-to-date devices. We also found that myopic mouse eyes showed decreased visual acuity on optokinetic response examination. Finally, we confirmed the anti-myopic effect of 1% atropine using this model, which showed its potential in drug screening. The strong phenotype, stable evaluation and the potential for gene manipulation utilizing the presented method in mice will accelerate the translational research of myopia.

Spatial Frequency Selectivity Is Impaired in Dopamine D2 Receptor Knockout Mice

Dopamine is a neurotransmitter implicated in several brain functions, including vision. In the present study, we investigated the impacts of the lack of D2 dopamine receptors on the structure and function of the primary visual cortex (V1) of D2-KO mice using optical imaging of intrinsic signals. Retinotopic maps were generated in order to measure anatomo-functional parameters such as V1 shape, cortical magnification factor, scatter, and ocular dominance. Contrast sensitivity and spatial frequency selectivity (SF) functions were computed from responses to drifting gratings. When compared to control mice, none of the parameters of the retinotopic maps were affected by D2 receptor loss of function. While the contrast sensitivity function of D2-KO mice did not differ from their wild-type counterparts, SF selectivity function was significantly affected as the optimal SF and the high cut-off frequency (p < 0.01) were higher in D2-KO than in WT mice. These findings show that the lack of function of D2 dopamine receptors had no influence on cortical structure whereas it had a significant impact on the spatial frequency selectivity and high cut-off. Taken together, our results suggest that D2 receptors play a specific role on the processing of spatial features in early visual cortex while they do not seem to participate in its development.

Prevalence and Related Factors for Myopia in School-Aged Children in Qingdao

Purpose

To investigate the prevalence and related factors for myopia in school-aged children in the Economic and Technological Development Zone of Qingdao, Eastern China.

Methods

A total of 4890 (aged 10 to 15 years) students were initially enrolled in this study. 3753 (76.75%) students with completed refractive error and questionnaire data were analyzed. The children underwent a comprehensive eye examination. Multiple logistic regression models were applied to assess possible factors associated with myopia.

Results

The prevalence of myopia increased as the children's grade increased (χ² = 560.584, P < 0.001). Low myopia was the main form of myopia in adolescent students (30.22%). With the growth of age, students spent significantly more time on near work (P = 0.03) and less time on outdoor activity (P < 0.001). In multivariate models, only the following variables were significantly associated with myopia: age, two myopic parents, outdoor activity time, and continuous near work without 5 min rest.

Conclusions

The prevalence of myopia increased as the grade increased. Age, two myopic parents, and continuous near work time without 5 min rest were risk factors for myopia. Outdoor activities had protective effect for myopia.

Association between parents' attitudes and behaviors toward children's visual care and myopia risk in school-aged children

The purpose of this survey was to determine the association of parents' attitudes and behaviors toward children's visual care with myopia risk in school-aged children.A total of 894 parents of school-aged children were investigated in primary and middle schools in the central and noncentral urban area in Wuhan through stratified cluster random sampling on July, 2015. We analyzed the association by the generalized linear mixed model.The results indicated that children with parents' high expectations of 1.5 or higher on their vision exhibited a decreased risk of myopia compared with 1.0 and 0.5 or lower (OR = 0.49, 95%CI = 0.36-0.67). Children whose parents only paid attention to their vision in junior and senior school and in primary school had an increased myopia risk than that in preschool (OR = 2.12, 95%CI = 1.01-4.45, and OR = 3.11, 95%CI = 1.28-7.58, respectively). Children whose parents ensured for their sufficient sleep had a decreased myopia risk (OR = 0.45, 95%CI = 0.24-0.85). Compared with children whose parents who never adjusted electronic devices' parameters, the odds ratio of sometimes was 0.49 (95%CI = 0.31-0.79), often 0.53 (95%CI = 0.33-0.85), and always 0.44 (95%CI = 0.26-0.75), respectively.Parents' attitudes and behaviors toward children's visual care are significantly associated with the myopia risk in school-aged children. Consequently, efforts should be made to educate parents on how they protect children's vision and reduce their risk of myopia.

Effect of dopamine on bone morphogenesis protein-2 expression in human retinal pigment epithelium

AIM

To investigate the effect of dopamine on bone morphogenesis protein-2 (BMP-2) expression in retinal pigment epithelium (RPE) cells in vitro.

METHODS

ARPE-19 cells as a human RPE cell line were cultured with dopamine for different times (2, 4, 6, 8, 12, 16 and 24h) or with different concentrations (0.1, 1, 2, 5, 10, 20, and 100 µg/mL) in vitro. BMP-2 mRNA expression level in ARPE-19 cells was analyzed with real-time polymerase chain reaction (PCR) analysis and BMP-2 protein level was measured with Western blot analysis. The active form of BMP-2 in the culture medium was measured with enzyme-linked immunosorbent assay (ELISA).

RESULTS

The expression level of BMP-2 increased significantly cultured with 20 µg/mL dopamine, at different time points (P<0.05). BMP-2 mRNA level peaked 2h and the protein level peaked at 6 and 8h after treatment. The concentrations of secreted BMP-2 elevated at 12h and peaked at 24h (P<0.05) in a time-dependent manner. Treated with 100 µg/mL dopamine for 6h, the expression levels of BMP-2 mRNA and protein in ARPE-19 cells were enhanced significantly compared to that in the untreated cells (P<0.05). And secreted BMP-2 protein in the cell culture supernatant was also increased (P<0.05).

CONCLUSION

Dopamine up-regulate BMP-2 expression in RPE cells, and this may be associated with its inhibitive effect on myopia development.

Animal Studies and the Mechanism of Myopia-Protection by Light?

Epidemiological studies have demonstrated that spending time outdoors during your childhood is protective against the development of myopia. It has been hypothesized that this protective effect is associated with light-induced increases in retinal dopamine levels, a critical neuromodulator that has long been postulated to be involved in the regulation of ocular growth. This paper, along with the paper entitled "What do animal studies tell us about the mechanism of myopia-protection by light?" discusses the evidence provided by animal models for this hypothesis.

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.

Changes in retinal metabolic profiles associated with form deprivation myopia development in guinea pigs

Retinal metabolic changes have been suggested to be associated with myopia development. However, little is known about either their identity or time dependent behavior during this sight compromising process. To address these questions, gas chromatography time-of-flight mass spectrometry (GC-TOF/MS) was applied to compare guinea pig retinal metabolite levels in form deprivation (FD) eyes at 3 days and 2 weeks post FD with normal control (NC) eyes. Orthogonal partial least squares (OPLS) models discriminated between time dependent retinal metabolic profiles in the presence and absence of FD. Myopia severity was associated with more metabolic pattern differences in the FD than in the NC eyes. After 3 days of FD, 11 metabolite levels changed and after 2 weeks the number of differences increased to 16. Five metabolites continuously decreased during two weeks of FD. Two-way ANOVA of the changes identified by OPLS indicates that 15 out of the 22 metabolites differences were significant. Taken together, these results suggest that myopia progression is associated with an inverse relationship between increases in glucose accumulation and lipid level decreases in form-deprived guinea pig eyes. Such changes indicate that metabolomic studies are an informative approach to identify time dependent retinal metabolic alterations associated with this disease.

Development of Experimental Myopia in Chicks in a Natural Environment

Purpose

The hypothesis that outdoor exposure might protect against myopia has generated much interest, although available data find only modest clinical efficacy. We tested the effect of outdoor rearing on form-deprivation myopia in chicks, a myopia model markedly inhibited by high-intensity indoor laboratory lighting.

Methods

Unilaterally goggled cohorts of White Leghorn chicks were maintained in a species-appropriate, outdoor rural setting during daylight hours to the extent permitted by weather. Control chicks were reared indoors with incandescent lighting. Besides ocular refraction and ultrasound, we determined dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) content in retina and vitreous and measured mRNA expression levels of selected clock and circadian rhythm-related genes in the retina/RPE.

Results

Myopia developed in the goggled eyes of all cohorts. Whereas outdoor rearing lessened myopia by 44% at 4 days, a protective effect was no longer evident at 11 days. Outdoor rearing had no consistent effect on retinal or vitreous content of dopamine or DOPAC. Conforming to prior data on form-deprivation myopia, retina and vitreous levels of DOPAC were reduced in goggled eyes. Compared with contralateral eyes, the retinal expression of clock and circadian rhythm-related genes was modestly altered in myopic eyes of chicks reared indoors or outdoors.

Conclusions

Outdoor rearing of chicks induces only a partial decrease of goggle-induced myopia that is not maintained, without evidence that retinal dopamine metabolism accounts for the partial myopia inhibition under these outdoor conditions. Although modest, alterations in retinal gene expression suggest that studying circadian signals might be informative for understanding refractive mechanisms.