Effects of atropine on refractive development, dopamine release, and slow retinal potentials in the chick

Topical Atropine for Myopia Control: A Review

Over the past decade, atropine has emerged as an effective intervention for preventing myopia in children. Multiple randomized controlled trials, mainly from Asia, have demonstrated the safety and efficacy of topical atropine for myopia control. Both efficacy and side effects exhibit a positive dose-response relationship. This review focuses on new data from studies with predominantly white populations, ethnicity-dependent differences in efficacy and side effects, and primary prevention of incident myopia with atropine.

Five-year results of atropine 0.01% efficacy in the myopia control in a European population

AIMS

To evaluate the efficacy and safety of 0.01% atropine eye-drops in controlling myopia progression over 5 years.

METHODS

Experimental, analytical, prospective, randomised and longitudinal study, in 361 right eyes from 361 children randomised into the control group (177 eyes without treatment) and treatment group (184 eyes with 0.01% atropine eye-drops). Children assigned to the treatment group used 0.01% atropine once a day every night and the control group's children did not use any treatment or placebo. All the subjects completed an eye examination every 6 months for the 5 years of follow-up. The examination included subjective and objective refraction with cycloplegia, axial length (AL), keratometry and anterior chamber depth (ACD) to evaluate the efficacy of the treatment. It also included the anterior and posterior pole examination to evaluate the safety of the treatment.

RESULTS

The SE increased -0.63±0.42D in children after 5 years of treatment with 0.01% atropine, while in the control group the increase was -0.92±0.56D. AL increased 0.26±0.28 mm in the treatment group compared with 0.49±0.34 mm in the control group. Atropine 0.01% showed an efficacy of 31.5% and 46.9% in the control of the SE and AL increase, respectively. ACD and keratometry did not have significant changes between groups.

CONCLUSIONS

Atropine 0.01% is effective in slowing myopia progression in a European population. There were no side effects after 5 years of 0.01% atropine.

Eye Diseases: When the Solution Comes from Plant Alkaloids

Plants are an incredible source of metabolites showing a wide range of biological activities. Among these, there are the alkaloids, which have been exploited for medical purposes since ancient times. Nowadays, many plant-derived alkaloids are the main components of drugs used as therapy for different human diseases. This review deals with providing an overview of the alkaloids used to treat eye diseases, describing the historical outline, the plants from which they are extracted, and the clinical and molecular data supporting their therapeutic activity. Among the different alkaloids that have found application in medicine so far, atropine and pilocarpine are the most characterized ones. Conversely, caffeine and berberine have been proposed for the treatment of different eye disorders, but further studies are still necessary to fully understand their clinical value. Lastly, the alkaloid used for managing hypertension, reserpine, has been recently identified as a potential drug for ameliorating retinal disorders. Other important aspects discussed in this review are different solutions for alkaloid production. Given that the industrial production of many of the plant-derived alkaloids still relies on extraction from plants, and the chemical synthesis can be highly expensive and poorly efficient, alternative methods need to be found. Biotechnologies offer a multitude of possibilities to overcome these issues, spanning from genetic engineering to synthetic biology for microorganisms and bioreactors for plant cell cultures. However, further efforts are needed to completely satisfy the pharmaceutical demand.

Effect of COVID-19 home confinement on the efficacy of orthokeratology, 0.01% atropine and combined treatment

PURPOSE

To investigate the effect of COVID-19 home confinement on the efficacy of the interventions for controlling myopia, and to select effective therapies to control myopia during COVID-19 confinement.

METHOD

Children (n = 164) aged 8-12 years with spherical equivalent refraction of -1.00 to -6.00 diopters were stratified into two age subgroups and randomly allocated into the control, 0.01% atropine, orthokeratology (ortho-k) and atropine combined ortho-k (ACO) groups. Axial length (AL) was measured at baseline, 6-, 12-, 18- and 24-month visits. The follow-up spanned the period before the COVID-19 outbreak, the period of the home confinement, and the period of the school reopening. Hence, the AL change in different periods was collected and compared. Data analysis was performed following the criteria of intention to treat (ITT).

RESULTS

All 164 children were involved in the ITT analysis. Compared to control, all interventions can still reduce the AL elongation during the COVID-19 home confinement period (all p < 0.05). However, the efficacy was compromised: individuals experienced more AL elongation during the COVID-19 home confinement period in the control, 0.01% atropine and ACO groups (all p < 0.05). Interestingly, in the ortho-k group, the difference was insignificant (p = 0.178), and the interaction between the intervention type (control vs. ortho-k) and the confinement severity was significant (p for interaction = 0.041), which is different from the atropine (p for interaction = 0.248) or ACO group (p for interaction = 0.988). These results were stable after being adjusted by other variables based on the multivariable regression model.

CONCLUSION

Ortho-k was less affected by the COVID-19 home confinement, which is potentially a better therapy for children in this high-risk environment. Further investigations are warranted to validate this issue.

The role of the serotonergic system in atropine's anti-myopic effects

The muscarinic cholinergic antagonist atropine is the most widely used pharmacological treatment for the visual disorder myopia (short-sightedness), the leading cause of low-vision worldwide. This study sought to better define the mechanism by which atropine inhibits myopic growth. Although classified as a muscarinic-cholinergic antagonist, atropine has been found to bind and modulate the activity of several non-cholinergic systems (e.g., serotonin). Thus, this study investigated whether the serotonergic system could underly atropine's anti-myopic effects. Using a chick model of myopia, we report that atropine's growth-inhibitory effects can be attenuated by pharmacological stimulation of the serotonin system. This may suggest that atropine can slow the development of myopia through inhibiting serotonergic receptor activity. We also observed that pharmacological antagonism of serotonergic receptors inhibits the development of experimental myopia in a dose-dependent manner, further demonstrating that modulation of serotonergic receptor activity can alter ocular growth rates. Finally, we found that neither experimental myopia, nor atropine treatment, induced a significant change in retinal serotonergic output (i.e., synthesis, transport, release and catabolism). This may suggest that, although myopic growth can be inhibited through modulation of serotonergic receptor activity (by atropine or serotonergic antagonists), this does not require a change in serotonin levels. These findings regarding a serotonergic mechanism for atropine may have significant ramifications for the treatment of human myopia. This includes assessing the use of atropine in patients who are also undergoing treatment to upregulate serotonergic signaling (e.g., serotonergic anti-depressants).

Parasympathetic and sympathetic control of emmetropization in chick

Emmetropization can be altered by temporal visual stimulation and the spectral properties of the visual environment. The goal of the current experiment is to test the hypothesis that there is an interaction between these properties and autonomic innervation. For that purpose, selective lesions of the autonomic nervous system were performed in chickens followed by temporal stimulation. Parasympathetic lesioning involved transection of both the ciliary ganglion and the pterygopalatine ganglion (PPG_CGX; n = 38), while sympathetic lesioning involved transection of the superior cervical ganglion (SCGX; n = 49). After one week of recovery, chicks were then exposed to temporally modulated light (3 days, 2 Hz, Mean: 680 lux) that was either achromatic (with blue [RGB], or without blue [RG]), or chromatic (with blue [B/Y] or without blue [R/G]). Control birds with lesions, or unlesioned, were exposed to white [RGB] or yellow [RG] light. Ocular biometry and refraction (Lenstar and a Hartinger refractometer) was measured before and after exposure to light stimulation. Measurements were statistically analyzed for the effects of a lack of autonomic input and the type of temporal stimulation. In PPG_CGX lesioned eyes, there was no effect of the lesions one-week post-surgery. However, after exposure to achromatic modulation, the lens thickened (with blue) and the choroid thickened (without blue) but there was no effect on axial growth. Chromatic modulation thinned the choroid with R/G. In the SGX lesioned eye, there was no effect of the lesion 1-week post-surgery. However, after exposure to achromatic modulation (without blue), the lens thickened and there was a reduction in vitreous chamber depth and axial length. Chromatic modulation caused a small increase in vitreous chamber depth with R/G. Both autonomic lesion and visual stimulation were necessary to affect the growth of ocular components. The bidirectional responses observed in axial growth and in choroidal changes suggest that autonomic innervation combined with spectral cues from longitudinal chromatic aberration may provide a mechanism for homeostatic control of emmetropization.

Atropine-eluting silicone contact lenses for myopia control

Myopia, also known as nearsightedness, is one of the prime reasons for vision impairment worldwide. Atropine in topical ophthalmic solutions (e.g., 0.01% atropine sulfate eye drops) is the primary medical treatment for controlling myopia, especially for pseudomyopia or true myopia in rapid progress. However, aqueous atropine solution is unstable and easily breaks down to tropic acid, which will result in vision blur. Drug-eluting contact lenses (CLs) have been explored as a potentially superior alternative to effectively control the drug release and improve the drug efficacy. In this work, an atropine-eluting contact lens was developed by encapsulating an atropine implant in a silicon-based contact lens, towards functioning in vision correction and controlling myopia. The safety and effectiveness of this atropine-eluting contact lens were verified with rabbit and guinea pig models. The results showed that the lenses reduced the side effects like mydriasis and no other adverse events were observed in rabbit eyes. More importantly, atropine-loaded lenses could effectively delay the progress of form-deprivation myopia with guinea pig eyes as the model. Thus, we concluded that atropine-eluting CLs prepared by implantation technology may be an option for the treatment of myopia.

Multifocal Contact Lenses and 0.01% Atropine Eye Drops for Myopia Control Study: Research Protocol for a 1-Year, Randomized, Four-Arm, Clinical Trial in Schoolchildren

OBJECTIVES

Previous studies have shown that combined use of orthokeratology and 0.01% atropine (AT) eye drops can strongly prevent axial elongation in myopic children. However, the efficacy of combined use with multifocal contact lens (MFCL) and 0.01% AT remains unclear. The aim of this trial is to clarify the efficacy of MFCL+0.01% AT combination therapy for myopia control and safety.

METHODS

This prospective study is a randomized, double-masked, placebo-controlled trial with four arms. A total of 240 children aged 6 to 12 years with myopia is recruited and randomly assigned to one of the four groups in a ratio of 1:1:1:1 as follows: group 1: MFCL+AT combination therapy, group 2: MFCL monotherapy, group 3: AT monotherapy, and group 4: placebo. The participants will continue the assigned treatment for 1 year. The primary and secondary outcomes are the comparisons of axial elongation and myopia progression in the four groups during the 1-year study period.

DISCUSSION

The present trial would determine whether the MFCL+AT combination therapy is more effective in slowing axial elongation and myopia progression in schoolchildren as compared with each monotherapy or placebo, and it also confirm acceptable safety of the combination therapy.

Myopia control in Mendelian forms of myopia

PURPOSE

To study the effectiveness of high-dose atropine for reducing eye growth in Mendelian myopia in children and mice.

METHODS

We studied the effect of high-dose atropine in children with progressive myopia with and without a monogenetic cause. Children were matched for age and axial length (AL) in their first year of treatment. We considered annual AL progression rate as the outcome and compared rates with percentile charts of an untreated general population. We treated C57BL/6J mice featuring the myopic phenotype of Donnai-Barrow syndrome by selective inactivation of Lrp2 knock out (KO) and control mice (CTRL) daily with 1% atropine in the left eye and saline in the right eye, from postnatal days 30-56. Ocular biometry was measured using spectral-domain optical coherence tomography. Retinal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured using high-performance liquid chromatography.

RESULTS

Children with a Mendelian form of myopia had average baseline spherical equivalent (SE) -7.6 ± 2.5D and AL 25.8 ± 0.3 mm; children with non-Mendelian myopia had average SE -7.3 ± 2.9 D and AL 25.6 ± 0.9 mm. During atropine treatment, the annual AL progression rate was 0.37 ± 0.08 and 0.39 ± 0.05 mm in the Mendelian myopes and non-Mendelian myopes, respectively. Compared with progression rates of untreated general population (0.47 mm/year), atropine reduced AL progression with 27% in Mendelian myopes and 23% in non-Mendelian myopes. Atropine significantly reduced AL growth in both KO and CTRL mice (male, KO: -40 ± 15; CTRL: -42 ± 10; female, KO: -53 ± 15; CTRL: -62 ± 3 μm). The DA and DOPAC levels 2 and 24 h after atropine treatment were slightly, albeit non-significantly, elevated.

CONCLUSIONS

High-dose atropine had the same effect on AL in high myopic children with and without a known monogenetic cause. In mice featuring a severe form of Mendelian myopia, atropine reduced AL progression. This suggests that atropine can reduce myopia progression even in the presence of a strong monogenic driver.

Analysis of the reports of low-concentration atropine in controlling myopia in children

PURPOSE

To evaluate the efficacy of 0.01% atropine to slow the progression of myopia in children.

METHODS

We searched PubMed, Embase, ClinicalTrials.gov, CNKI, Cqvip and Wan fang databases from inception to January 2022, including RCTs (randomized controlled trials) and non-RCTs (non-randomized controlled trials). The search strategy was 'myopia' OR 'refractive error' and 'atropine.' Two researchers independently reviewed the articles, and stata12.0 was used for meta-analysis. The Jadad score was used to assess the quality of RCT, and the Newcastle-Ottawa scale was used for non-RCTs.

RESULTS

Five RCTs and two non-RCTs (1 prospective non-randomized controlled study, 1 retrospective cohort study) were identified (including 1000 eyes). Results of the meta-analysis showed statistical heterogeneity among the 7 included studies (P=0. 026, I2 =47.1%). According to different durations of atropine use - 4 months, 6 months and greater than 8 months, subgroup analysis results showed that the axial elongation of all experimental groups relative to control groups were respectively -0.03mm (95% [CI], (confidence interval), -0.07 to 0.01), -0.07mm (95% [CI], -0.10 to -0.05), -0.09mm (95% [CI], -0.12 to -0.06). Each P was greater than 0.05, which indicated that there is little heterogeneity among the subgroups.

CONCLUSIONS

In this meta-analysis of the short-term efficacy of atropine in myopia patients, it was found that there was little heterogeneity when grouped by usage time. It is suggested that the use of atropine in the treatment of myopia is not only related to its concentration but also related to the duration of use.

Gamma-Synuclein Dysfunction Causes Autoantibody Formation in Glaucoma Patients and Dysregulation of Intraocular Pressure in Mice

Dysregulation of intraocular pressure (IOP) is one of the main risk factors for glaucoma. γ-synuclein is a member of the synuclein family of widely expressed synaptic proteins within the central nervous system that are implicated in certain types of neurodegeneration. γ-synuclein expression and localization changes in the retina and optic nerve of patients with glaucoma. However, the mechanisms by which γ-synuclein could contribute to glaucoma are poorly understood. We assessed the presence of autoantibodies to γ-synuclein in the blood serum of patients with primary open-angle glaucoma (POAG) by immunoblotting. A positive reaction was detected for five out of 25 patients (20%) with POAG. Autoantibodies to γ-synuclein were not detected in a group of patients without glaucoma. We studied the dynamics of IOP in response to IOP regulators in knockout mice (γ-KO) to understand a possible link between γ-synuclein dysfunction and glaucoma-related pathophysiological changes. The most prominent decrease of IOP in γ-KO mice was observed after the instillation of 1% phenylephrine and 10% dopamine. The total protein concentration in tear fluid of γ-KO mice was approximately two times higher than that of wild-type mice, and the activity of neurodegeneration-linked protein α2-macroglobulin was reduced. Therefore, γ-synuclein dysfunction contributes to pathological processes in glaucoma, including dysregulation of IOP.

Changes of Choroidal Thickness in Children after Short-Term Application of 1% Atropine Gel

INTRODUCTION

The aim of the study was to assess changes in choroidal thickness (ChT) after administration of 1% atropine for 1 week in myopic, emmetropic, and hyperopic children.

METHODS

A total of 235 children aged 4-8 years, which included 46 myopia, 34 emmetropia, and 155 hyperopia patients, were recruited and divided into three groups according to the spherical equivalent with the use of 1% atropine twice a day for 1 week. The ChT was measured at baseline and 1 week.

RESULTS

In the myopia and emmetropia groups, following administration of 1% atropine gel, the ChT thickened significantly under the fovea (i.e., from 278.29 ± 53.01 μm to 308.24 ± 57.3 μm, p < 0.05; from 336.10 ± 78.60 μm to 353.46 ± 70.22 μm, p < 0.05, respectively), and at all intervals from the fovea, while in the hyperopia group, there was no significant difference in the ChT except the nasal side (p < 0.05).

CONCLUSION

Topical administration of 1% atropine gel for 1 week significantly increased the subfoveal and parafoveal ChT in children with myopia and emmetropia. Atropine did not increase the ChT in hyperopic children, except on the nasal side.

Gene Expression Signatures of Contact Lens-Induced Myopia in Guinea Pig Retinal Pigment Epithelium

Purpose

To identify key retinal pigment epithelium (RPE) genes linked to the induction of myopia in guinea pigs.

Methods

To induce myopia, two-week-old pigmented guinea pigs (New Zealand strain, n = 5) wore −10 diopter (D) rigid gas-permeable contact lenses (CLs), for one day; fellow eyes were left without CLs and served as controls. Spherical equivalent refractive errors (SE) and axial length (AL) were measured at baseline and one day after initiation of CL wear. RNA sequencing was applied to RPE collected from both treated and fellow (control) eyes after one day of CL-wear to identify related gene expression changes. Additional RPE-RNA samples from treated and fellow eyes were subjected to quantitative real-time PCR (qRT-PCR) analysis for validation purposes.

Results

The CLs induced myopia. The change from baseline values in SE was significantly different (P = 0.016), whereas there was no significant difference in the change in AL (P = 0.10). RNA sequencing revealed significant interocular differences in the expression in RPE of 13 genes: eight genes were significantly upregulated in treated eyes relative to their fellows, and five genes, including bone morphogenetic protein 2 (Bmp2), were significantly downregulated. The latter result was also confirmed by qRT-PCR. Additional analysis of differentially expressed genes revealed significant enrichment for bone morphogenetic protein (BMP) and TGF-β signaling pathways.

Conclusions

The results of this RPE gene expression study provide further supporting evidence for an important role of BMP2 in eye growth regulation, here from a guinea pig myopia model.

The Association of Choroidal Thickening by Atropine With Treatment Effects for Myopia: Two-Year Clinical Trial of the Low-concentration Atropine for Myopia Progression (LAMP) Study

PURPOSE

To evaluate longitudinal changes in subfoveal choroidal thickness (SFChT) among children receiving atropine 0.05%, 0.025%, or 0.01% over 2 years and their associations with treatment outcomes in myopia control.

DESIGN

Double-blinded randomized controlled trial.

METHODS

SFChT was measured at 4-month intervals using spectral domain optical coherence tomography. Cycloplegic spherical equivalent (SE), axial length (AL), best-corrected visual acuity, parental SE, outdoor time, near work diopter hours, and treatment compliance were also measured.

RESULTS

314 children were included with qualified choroidal data. The 2-year changes in SFChT from baseline were 21.15 ± 32.99 µm, 3.34 ± 25.30 µm, and -0.30 ± 27.15 µm for the atropine 0.05%, 0.025%, and 0.01% groups, respectively (P < .001). A concentration-dependent response was observed, with thicker choroids at higher atropine concentrations (β = 0.89, P < .001). Mean SFChT thickness significantly increased at 4 months in the atropine 0.025% (P = .001) and 0.05% groups (P < .001) and then remained stable until the end of the second year (P > .05 for all groups). Over 2 years, an increase in SFChT was associated with slower SE progression (β = 0.074, P < .001) and reduced AL elongation (β = -0.045, P < .001). In the mediation analysis, 18.45% of the effect on SE progression from atropine 0.05% was mediated via its choroidal thickening.

CONCLUSIONS

Low concentration atropine induced a choroidal thickening effect along a concentration-dependent response throughout the treatment period. The choroidal thickening was associated with a slower SE progression and AL elongation among all the treatment groups. Choroidal response can be used for assessment of long-term treatment outcomes and as a guide for concentration titrations of atropine.

The Role of Atropine in Preventing Myopia Progression: An Update

Several approaches have been investigated for preventing myopia progression in children and teenagers. Among them, topical atropine has shown promising results and it is being adopted in clinical practice more and more frequently. However, the optimal formulation and treatment algorithm are still to be determined. We discuss the pharmacokinetic, pharmacodynamic, clinical, and tolerability profile revealed first by the multicenter, randomized ATOM 1 and 2 trials and, more recently, by the LAMP Study. Results from these trials confirmed the efficacy of low-concentration atropine with a concentration-dependent response. Although atropine at 0.025% and 0.05% concentrations has shown the most encouraging results in large-scale studies, these formulations are not yet commonplace in worldwide clinical practice. Moreover, their rebound effect and the possibility of reaching a stabilization effect have not been fully investigated with real-life studies. Thus, further larger-scale studies should better characterize the clinical efficacy of atropine over longer follow-up periods, in order to define the optimal dosage and treatment regimen.

Parasympathetic innervation of emmetropization

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

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.

Atropine Affects the Outer Retina During Inhibiting Form Deprivation Myopia in Guinea Pigs

PURPOSE

Atropine has been proven to be effective in retarding myopia progression. However, the underlying mechanism remains unknown. Our purpose was to detect morphological and functional changes caused by atropine during myopic inhibition.

METHOD

Twenty 2-week-old guinea pigs were randomly assigned to either the saline group (n = 10) or the atropine group (n = 10). Form-deprived myopia (FDM) and intravitreal injections were applied on the right eyes. The injections were given every 3 days, lasting for 2 weeks. The left eyes served as control. Ocular refraction, axial length, retinal, and choroidal thickness were collected at the start and the end of the experiment. Retinal function was evaluated via full-field electroretinogram (ERG) at the end of treatment.

RESULTS

The interocular differences (experimental eye minus control eye) of refraction error (RE), vitreous chamber depth (VCD), and axial length (AL) in the saline group were significantly greater than those in the atropine group (RE, VCD: P < .001, AL: P < .0001). The differences in choroidal thickness between the two groups did not reach statistical significance. However, a decreasing trend of choroidal thickness was observed in the saline group but not in the atropine group. Furthermore, the interocular differences of total retinal and outer retinal thickness in the atropine group were much thicker than in the saline group (P < .001 and P < .01, respectively). The treatment did not affect inner retinal thickness. In photopic ERG, the atropine-treated FDM eyes showed significantly greater a-wave amplitudes compared to the saline group.

CONCLUSION

During the process of inhibiting FDM, atropine showed an effect on the outer retina, most likely on the cones, in guinea pigs.

Retinal OFF-Pathway Overstimulation Leads to Greater Accommodation-Induced Choroidal Thinning

Purpose

To examine the interactions between accommodation and overstimulation of the retinal ON- and OFF-pathways, and their association with changes in choroidal thickness (ChT) and vascularity.

Methods

Optical coherence tomography imaging of the choroid of twenty young adults (ages 25 ± 5 years) was performed before and after a series of 30-minute-long viewing tasks, including reading a bright text on dark background (ON-pathway overstimulation) and dark text on bright background (OFF-pathway overstimulation), and a control task of viewing a movie with unbiased ON-/OFF-pathway activation. The viewing tasks were performed with relaxed, and 5 diopter (D) accommodation (induced by soft contact lenses) demands. Both reading texts were matched for the mean luminance (35 cd/m²), luminance contrast (87%), and letter size (approximately 11.8 arc minutes). The change in ChT from baseline associated with contrast polarity and accommodation was examined using linear mixed model analysis.

Results

The subfoveal ChT decreased significantly by −7 ± 1 µm with 5 D accommodation compared with relaxed accommodation (−3 ± 1 µm; P < 0.001), and by −9 ± 1 µm with OFF-pathway compared with ON-pathway overstimulation (−4 ± 1 µm; P = 0.002) and the control condition (−2 ± 1 µm; P < 0.001). Overstimulation of the OFF-pathway, but not the ON-pathway, resulted in a significantly greater choroidal thinning compared with the control condition, both at relaxed (−7 ± 1 µm; P = 0.003) and 5 D (−11 ± 1 µm; P = 0.005) accommodation levels. Similar changes were also observed for macular total, stromal, and luminal ChT.

Conclusions

Retinal OFF-pathway stimulation enhanced the choroidal thinning associated with accommodation, thereby providing a potential mechanism that involves accommodation and the retinal OFF-signaling pathway, linking near work and myopia.

Prevention of Choroidal Thinning by 0.01% Atropine Administered 24 h Before Exposure to Hyperopic Blur in Young Myopes

Purpose: To evaluate the persistence of atropine's effect upon choroidal thickness and ocular biometrics and its interaction with hyperopic blur in a population of young adult myopes. Methods: Twenty young (aged 18-35 years) myopic participants with spherical equivalent refractive error of -0.75 to -6.00 D (mean ± SD -2.85 ± 1.64 D) had subfoveal choroidal thickness (SFCT) measurements derived from scans collected from the right eye only with a SD-OCT instrument (Copernicus SOCT-HR) before, as well as 60 min following the introduction of 3 testing conditions: (1) placebo/hyperopic (-3 D) blur, (2) placebo/hyperopic blur one day after administration of 0.01% atropine, and (3) placebo/no blur. Each combination of blur and pharmacological agent was tested on a separate day at approximately the same time of day between 9 am and 2 pm. Results: Repeated measures ANOVA revealed that hyperopic blur and placebo were associated with a decrease in choroidal thickness (mean change: -10.7 ± 2.7 μm, P < 0.001 after 60 min), whereas administration of 0.01% atropine one day before the introduction of hyperopic blur prevented the thinning of the choroid (mean change of +1.1 ± 3.7 μm after 60 min) compared to baseline (both, P > 0.05). There was also no significant difference between the baseline choroidal thickness measurements for any of the conditions tested. Conclusion: Low dose atropine can inhibit signals associated with hyperopic defocus that cause thinning of the choroid for at least 24 h after initial instillation.

Congenital stationary night blindness: an update and review of the disease spectrum in Saudi Arabia

Congenital stationary night blindness (CSNB) is a group of rare, mainly stationary disorders of the retina, resulting from dysfunction of several specific and essential visual processing mechanisms. The inheritance is often recessive and as such, CSNB may be more common among populations with a high degree of consanguinity. Here, we present a topic update and a review of the clinical and molecular genetic spectrum of CSNB in Saudi Arabia. Since a major review article on CSNB in 2015, which described 17 genes underlying CSNB, an additional four genes have been incriminated in autosomal recessive CSNB: RIMS2, GNB3, GUCY2D and ABCA4. These have been associated with syndromic cone-rod synaptic disease, ON bipolar cell dysfunction with reduced cone sensitivity, CSNB with dysfunction of the phototransduction (Riggs type) and CSNB with cone-rod dystrophy, respectively. In Saudi Arabia, a total of 24 patients with CSNB were identified, using a combination of literature search and retrospective study of previously unpublished cases. Recessive mutations in TRPM1 and CABP4 accounted for the majority of cases (5 and 13 for each gene, respectively). These genes were associated with complete (cCSNB) and incomplete (icCSNB), respectively, and were associated with high myopia in the former and hyperopia in the latter. Four novel mutations were identified. For the first time, we describe the fundus albipunctatus in two patients from Saudi Arabia, caused by recessive mutation in RDH5 and RPE65, where the former in addition featured findings compatible with cone dystrophy. No cases were identified with any dominantly inherited CSNB.

Transcriptome-based insights into gene networks controlling myopia prevention

Myopia (short-sightedness), usually caused by excessive elongation of the eye during development, has reached epidemic proportions worldwide. In animal systems including the chicken model, several treatments have been shown to inhibit ocular elongation and experimental myopia. Although diverse in their apparent mechanism of action, each one leads to a reduction in the rate of ocular growth. We hypothesize that a defined set of retinal molecular changes may underlie growth inhibition, irrespective of the treatment agent used. Accordingly, across five well-established but diverse methods of inhibiting myopia, significant overlap is seen in the retinal transcriptome profile (transcript levels and alternative splicing events) in chicks when analyzed by RNA-seq. Within the two major pathway networks enriched during growth inhibition, that of cell signaling and circadian entrainment, transcription factors form the largest functional grouping. Importantly, a large percentage of those genes forming the defined retinal response are downstream targets of the transcription factor EGR1 which itself shows a universal response to all five growth-inhibitory treatments. This supports EGR1's previously implicated role in ocular growth regulation. Finally, by contrasting our data with human linkage and GWAS studies on refractive error, we confirm the applicability of our study to the human condition. Together, these findings suggest that a universal set of transcriptome changes, which sit within a well-defined retinal network that cannot be bypassed, is fundamental to growth regulation, thus paving a way for designing novel targets for myopia therapies.

Insights into the mechanism of atropine's anti-myopia effects: evidence against cholinergic hyperactivity and modulation of dopamine release

Background and Purpose

The ability of the muscarinic cholinergic antagonist atropine to inhibit myopia development in humans and animal models would suggest that cholinergic hyperactivity may underlie myopic growth. To test this, we investigated whether cholinergic agonists accelerate ocular growth rates in chickens. Furthermore, we investigated whether atropine alters ocular growth by downstream modulation of dopamine levels, a mechanism postulated to underlie its antimyopic effects.

Experimental Approach

Muscarinic (muscarine and pilocarpine), nicotinic (nicotine) and non‐specific (oxotremorine and carbachol) cholinergic agonists were administered to chicks developing form‐deprivation myopia (FDM) or chicks that were otherwise untreated. Vitreal levels of dopamine and its primary metabolite 3,4‐dihydroxyphenylacetic acid (DOPAC) were examined using mass spectrometry MS in form‐deprived chicks treated with atropine (360, 15 or 0.15 nmol). Further, we investigated whether dopamine antagonists block atropine's antimyopic effects.

Key Results

Unexpectedly, administration of each cholinergic agonist inhibited FDM but did not affect normal ocular development. Atropine only affected dopamine and DOPAC levels at its highest dose. Dopamine antagonists did not alter the antimyopia effects of atropine.

Conclusion and Implications

Muscarinic, nicotinic and non‐specific cholinergic agonists inhibited FDM development. This indicates that cholinergic hyperactivity does not underlie myopic growth and questions whether atropine inhibits myopia via cholinergic antagonism. This study also demonstrates that changes in retinal dopamine release are not required for atropine's antimyopic effects. Finally, nicotinic agonists may represent a novel and more targeted approach for the cholinergic control of myopia as they are unlikely to cause the anterior segment side effects associated with muscarinic treatment.

A retrospective analysis of the therapeutic effects of 0.01% atropine on axial length growth in children in a real-life clinical setting

BACKGROUND

Several randomized controlled studies have demonstrated the beneficial effects of 0.01% atropine eye drops on myopia progression in children. However, treatment effects may be different in a routine clinical setting. We performed a retrospective analysis of our clinical data from children to investigate the effect of 0.01% atropine eye drops on myopia progression in a routine clinical setting.

METHODS

Atropine-treated children were asked to instill one drop of 0.01% atropine in each eye every evening at 5 days a week. Myopic children who did not undergo atropine treatment served as controls. Objective refraction and ocular biometry of 80 atropine-treated and 103 untreated children at initial visit and 1 year later were retrospectively analyzed.

RESULTS

Myopic refractions in the treated and untreated children at initial visit ranged from -0.625 to -15.25 D (-4.21 ± 2.90 D) and from -0.125 to -9.375 D (-2.92 ± 1.77 D), respectively. Ages at initial visit ranged from 3.2 to 15.5 years (10.1 ± 2.7 years) in the treated and from 3.4 to 15.5 years (11.2 ± 3.0 years) in untreated children. Two-factor ANOVA for age and atropine effects on axial length growth confirmed that axial length growth rates declined with age (p<0.0001) and revealed a significant inhibitory effect of atropine on axial length growth (p<0.0015). The atropine effect on axial length growth averaged to 0.08 mm (28%) inhibition per year. Effects on refraction were not statistically significant.

CONCLUSION

The observed atropine effects were not very distinctive: Statistical analysis confirmed that atropine reduced axial length growth, but to an extent of minor clinical relevance. It was also shown that beneficial effects of 0.01% atropine may not be obvious in each single case, which should be communicated with parents and resident ophthalmologists.

Effects of Atropine Treatment on Choroidal Thickness in Myopic Children

Purpose

To examine the changes in choroidal thickness (ChT) after 6 months of 1% or 0.01% atropine treatment and the independent factors associated with eye elongation.

Methods

A total of 207 myopic children aged 6 to 12 years were recruited and randomly assigned to groups A and B in a ratio of 1:1. Participants in group A received 1% atropine once a day for 1 week, and then once a week for 23 weeks. Participants in group B received 0.01% atropine once a day for 6 months. ChT and internal axial length (IAL) were measured at baseline, 1 week, 3 months, and 6 months.

Results

In group A, the ChT significantly increased after a 1-week loading dose of 1% atropine (26 ± 14 µm; P < 0.001) and the magnitude of increase stabilized throughout the following weekly treatment. The internal axial length did not significantly change at the 6-month visit (−0.01 ± 0.11 mm; P = 0.74). In contrast, a decreased ChT (−5 ± 17 µm; P < 0.001) and pronounced eye elongation (0.19 ± 0.12 mm; P < 0.001) were observed in group B after 6 months. Multivariable regression analysis showed that less increase in ChT at the 1-week visit (P = 0.03), younger age (P < 0.001), and presence of peripapillary atrophy (P = 0.001) were significantly associated with greater internal axial length increase over 6 months in group A.

Conclusions

One percent atropine could increase the ChT, whereas 0.01% atropine caused a decrease in ChT after 6 months of treatment. For participants receiving 1% atropine, the short-term increase in ChT was negatively associated with long-term eye elongation. Younger age and the presence of peripapillary atrophy were found to be risk factors for greater eye elongation.

Update and guidance on management of myopia. European Society of Ophthalmology in cooperation with International Myopia Institute

The prevalence of myopia is increasing extensively worldwide. The number of people with myopia in 2020 is predicted to be 2.6 billion globally, which is expected to rise up to 4.9 billion by 2050, unless preventive actions and interventions are taken. The number of individuals with high myopia is also increasing substantially and pathological myopia is predicted to become the most common cause of irreversible vision impairment and blindness worldwide and also in Europe. These prevalence estimates indicate the importance of reducing the burden of myopia by means of myopia control interventions to prevent myopia onset and to slow down myopia progression. Due to the urgency of the situation, the European Society of Ophthalmology decided to publish this update of the current information and guidance on management of myopia. The pathogenesis and genetics of myopia are also summarized and epidemiology, risk factors, preventive and treatment options are discussed in details.

Atropine in topical formulations for the management of anterior and posterior segment ocular diseases

INTRODUCTION

Atropine is an old-known drug which is gaining increasing attention due to the myriad of therapeutic effects it may trigger on eye structures. Nevertheless, novel applications may require more adequate topical formulations.

AREAS COVERED

This review aims to gather the existing knowledge about atropine and its clinical applications in the ophthalmological field when administered topically. Atropine ocular pharmacokinetics is paid a special attention, including recent evidences of the capability of the drug to access to the posterior segment. Ocular bioavailability and systemic bioavailability are counterbalanced. Finally, limitations of traditional dosage forms and potential advantages of under investigation delivery systems are analyzed.

EXPERT OPINION

Mydriasis and cyclopegia have been widely exploited for eye examination, management of anterior segment diseases, and more recently as antidotes of chemical weapons. Improved knowledge on drug receptors and related pathways explains atropine repositioning as an outstanding tool to prevent myopia. The ease with which atropine penetrates ocular tissues is a double edged sword, that is, while it ensures therapeutic levels in the posterior segment, the unspecific distribution causes a wide variety of untoward effects. The design of formulations that can selectively deliver atropine to the target tissue for each specific application is an urgent unmet need.

Effects of Mydriatics on Rod/Cone- and Melanopsin-driven Pupil Responses

SIGNIFICANCE

Pupillometry protocols evaluating rod/cone- and melanopsin-driven responses often use mydriatics to ensure maximal stimulus exposure; however, retinal effects of mydriatics are not fully understood. We demonstrate that dilation with either atropine or phenylephrine results in similar enhancements of rod/cone- and melanopsin-driven pupil responses.

PURPOSE

The purposes of this study were to compare the effects of atropine, a muscarinic antagonist, and phenylephrine, an adrenergic agonist, on consensual pupil responses and to assess the repeatability of pupil metrics without mydriasis.

METHODS

Right eye pupil responses of 20 adults aged 21 to 42 years were recorded before and 45 minutes after instillation of 0.5% atropine or 2.5% phenylephrine in the left eye. Stimuli were presented to the left eye and included six alternating 1-second 651-nm "red" and 456-nm "blue" flashes. Metrics included baseline pupil diameter, maximal constriction, 6- and 30-second post-illumination pupil responses, and early (0 to 10 seconds) and late (10 to 30 seconds) areas under the curve.

RESULTS

Dilation of the stimulated eye with either mydriatic significantly increased the 6-second post-illumination pupil response and early and late areas under the curve for blue stimuli, and early area under the curve for red stimuli (P < .05 for all). Melanopsin-driven post-illumination pupil responses, achieved with either phenylephrine or atropine, did not significantly differ from each other (P > .05 for all). Without mydriasis, intersession intraclass correlation coefficients for pupil metrics were 0.63 and 0.50 (6- and 30-second post-illumination pupil responses, respectively) and 0.78 and 0.44 (early and late areas under the curve, respectively) for blue stimuli, with no significant difference between sessions (P > .05 for all).

CONCLUSIONS

Dilation with phenylephrine or atropine resulted in similar enhancements of the rod/cone- and melanopsin-driven pupil responses, despite differing mechanisms. Early pupil metrics without mydriasis demonstrated moderate to good intersession repeatability.

Biological Mechanisms of Atropine Control of Myopia

Myopia is a global problem that is increasing at an epidemic rate in the world. Although the refractive error can be corrected easily, myopes, particularly those with high myopia, are susceptible to potentially blinding eye diseases later in life. Despite a plethora of myopia research, the molecular/cellular mechanisms underlying the development of myopia are not well understood, preventing the search for the most effective pharmacological control. Consequently, several approaches to slowing down myopia progression in the actively growing eyes of children have been underway. So far, atropine, an anticholinergic blocking agent, has been most effective and is used by clinicians in off-label ways for myopia control. Although the exact mechanisms of its action remain elusive and debatable, atropine encompasses a complex interplay with receptors on different ocular tissues at multiple levels and, hence, can be categorized as a shotgun approach to myopia treatment. This review will provide a brief overview of the biological mechanisms implicated in mediating the effects of atropine in myopia control.

Comparisons of atropine versus cyclopentolate cycloplegia in myopic children

CLINICAL RELEVANCE

In clinical practice, 1% atropine and 1% cyclopentolate are used as cycloplegia agents to diagnose refractive error. The influence of 1% atropine on ocular biometry is obscure, and the impact of 1% cyclopentolate remains controversial.

BACKGROUND

This study aims to compare the effects of atropine versus cyclopentolate cycloplegia on ocular biometry in myopic children and to determine the sites of action for atropine.

METHODS

A total of 207 myopic children aged 6-12-years were included in the analysis. All participants underwent comprehensive eye examinations before and after cyclopentolate cycloplegia, after which they were randomly assigned into two groups, A and B, in a ratio of 1:1, to receive 1% or 0.01% atropine, respectively. The treatment was administered once every night for a week. Participants were re-examined one week later.

RESULTS

Cyclopentolate cycloplegia caused a decrease in choroidal thickness (-3 ± 9 μm, p = 0.001), elongation of axial length (9 ± 16 μm, p < 0.001), loss of lens power (-0.14 ± 0.37 dioptre, p < 0.001), and a hyperopic shift (0.14 ± 0.22 dioptre, p < 0.001) in both groups. However, ocular biometry showed different changes after one-week use of 1% or 0.01% atropine (all p < 0.001). In Group A, choroid thickening (24 ± 13 μm, p < 0.001) and reduced axial length (-30 ± 27 μm, p < 0.001) were observed after atropine cycloplegia, with greater changes in lens power (0.50 ± 0.37 dioptre, p < 0.001) and spherical equivalent (0.52 ± 0.23 dioptre, p < 0.001). Group B showed a slight increase in choroidal thickness following one-week use of 0.01% atropine (6 ± 9 μm, p < 0.001), but other biometric measures showed no significant changes.

CONCLUSION

Cyclopentolate and atropine cycloplegia have different effects on ocular biometry. Both 1% cyclopentolate cycloplegia and 0.01% atropine resulted in choroidal thickening, indicating that the choroid may be a site of action for atropine.

Pre-treatment with Scopolamine Naturally Suppresses Japanese Encephalitis Viral Load in Embryonated Chick Through Regulation of Multiple Signaling Pathways

Suitable recognition of invasive microorganisms is a crucial factor for evoking a strong immune response that can combat the pathogen. Toll-like receptors (TLRs) play a pivotal role in the induction of this innate immune response through stimulation of interferons (IFNs) that control viral replication in the host via distinct signaling pathways. Though the antiviral property of Atropa belladonna has been established, yet the role of one of its active components scopolamine in modulating various factors of the innate immune branch has not yet been investigated until date. Thus, the present study was conducted to assess the antiviral effects of scopolamine and its immunomodulatory role against Japanese encephalitis virus (JEV) infections in embryonated chick. Pre-treatment with scopolamine hydrobromide showed a significant decrease in the viral loads of chorioallantoic membrane (CAM) and brain tissues. Molecular docking analysis revealed that scopolamine hydrobromide binds to the active site of non-structural protein 5 (NS5) that has enzymatic activities required for replication of JEV, making it a highly promising chemical compound against the virus. The binding contributions of different amino acid residues at or near the active site suggest a potential binding of this compound. Pre-treatment with the scopolamine hydrobromide showed significant upregulation of different TLRs like TLR3, TLR7, and TLR8, interleukins like IL-4, and IL-10, as well as IFNs and their regulatory factors. However, virus-infected tissues (direct infection group) exhibited higher TLR4 expression as compared to scopolamine hydrobromide pre-treated, virus-infected tissues (medicine pre-treated group). These results indicate that scopolamine hydrobromide contributes much to launch antiviral effects by remoulding the TLR and IFN signaling pathways that are involved in sensing and initiating the much-needed anti-JEV responses.

Comparison of Administration of 0.02% Atropine and Orthokeratology for Myopia Control

OBJECTIVE

To compare the efficacies of 0.02% atropine eye drops and orthokeratology to control axial length (AL) elongation in children with myopia.

METHODS

In this historical control study, 247 children with myopia whose administration of 0.02% atropine (n=142) or underwent orthokeratology from an earlier study (n=105, control group) were enrolled. Data on AL and other baseline parameters were recorded at baseline and after 1 and 2 years of treatment.

RESULTS

The mean changes in AL in the first and second years of treatment were 0.30±0.21 and 0.28±0.20 mm, respectively, in the 0.02% atropine group and 0.16±0.20 and 0.20±0.16 mm, respectively, in the orthokeratology group. Axial length elongations after 2 years of treatment were 0.58±0.35 and 0.36±0.30 mm (P=0.007) in the 0.02% atropine and orthokeratology groups, respectively. Multivariate regression analyses showed that the AL elongation was significantly faster in the 0.02% atropine group than in the orthokeratology group (β=0.18, P=0.009). In multivariate regression analyses, younger age and shorter baseline AL were associated with a rapid AL elongation in the 0.02% atropine group (βage=-0.04, P=0.01; βAL=-0.17, P=0.03), while younger age, lower baseline spherical equivalent refractive error (SER), and shorter baseline AL were associated with a greater increase in AL in the orthokeratology group (βage=-0.03, P=0.04; βSER=0.06, P=0.03; βAL=-0.11, P=0.009). Faster AL elongation was found in the 0.02% atropine group compared with the orthokeratology group at higher baseline SER (P=0.04, interaction test).

CONCLUSION

Within the limits of this study design, orthokeratology seems to be a better method for controlling AL elongation compared with administration of 0.02% atropine in children with higher myopia over a treatment period of 2 years.

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.

The acute effect of atropine eye drops on the human full-field electroretinogram

PURPOSE

Atropine eye drops are a common and effective treatment for slowing myopia progression, but the site and mode of action of atropine in controlling myopia are unclear. We investigated the early retinal sites of action of atropine by examining its effects on the human full-field electroretinogram (ffERG).

METHOD

Baseline ffERGs were recorded in both eyes of 24 healthy subjects (mean ± SD: 21.0 ± 2.3 years; spherical equivalent refraction, range: + 1.63 to - 0.75 D) using 6 standard ISCEV protocols, 30 min after bilateral pupil dilation with 1% Tropicamide. Atropine (1 drop, 0.1%) was then instilled into the non-dominant eye. 24 h later, ffERGs were again recorded in both eyes. Ratios (post-atropine: pre-atropine) of dark-adapted (DA) and light-adapted (LA) ffERGs were compared between atropine-treated and control eyes using multivariate repeated measures general linear models.

RESULTS

Atropine-treated eyes responded with 14% lower DA3.0 OP (oscillatory potential) amplitude (p = 0.003) and 4% delay in the DA10.0 a-wave peak time (p = 0.00099) compared with control eyes. Amplitudes and peak times were not different between atropine-treated and control eyes for DA0.01, LA3.0, and LA3.0 flicker ERGs. While atropine caused a small (1.26 mm², p = 0.03) extra increase in pupil area in the treated eye, atropine-induced changes in ffERG responses bore no relationship with changes in pupil area (R²= 2-5%, p > 0.05).

CONCLUSIONS

The observed changes in oscillatory potentials corroborate previous findings that atropine affects neural activity in the inner retina. However, observed changes to the a-wave suggest that atropine also affects activity in photoreceptors.

Peripheral Refraction in Myopic Children with and without Atropine Usage

Purpose

To compare the patterns of relative peripheral refractions of myopic children who were currently on atropine treatment for myopia control and myopic children who did not use atropine.

Methods

Chinese children (n = 209) aged 7 to 12 years participated in the study, 106 used atropine and 103 did not. Participants were also classified into three groups: emmetropes (SE: +0.50 to −0.50 D), low myopes (SE: −0.50 to −3.00 D), and moderate myopes (SE: −3.00 to −6.00 D). The central and peripheral refractions along the horizontal meridians (for both nasal and temporal fields) were measured in 10-degree steps to 30 degrees.

Results

There were no statistically significant differences in spherical equivalent and astigmatism of the three refractive groups in either the nasal or temporal retina. The atropine group showed a significant relative myopia in the temporal 30° field in spherical equivalent compared to the emmetropic group (t₄₉ = 3.36, P=0.02). In eyes with low myopia, the atropine group had significant relative myopia in the nasal 30° and temporal 30° fields (t₁₁₈ = 2.59, P=0.01; t₁₁₈ = 2.06, P=0.04), and it is also observed at 20° and 30° of the nasal field for the moderate myopic group (t₃₆ = 2.37, P=0.02; t_2.84 = 2.84, P=0.01).

Conclusion

Significant differences in relative peripheral refraction were found between the atropine group and its controls. The findings suggested that the eyes that received atropine may have a less prolate shape and thus explain why using atropine is effective in controlling myopia progression.

Studies on retinal mechanisms possibly related to myopia inhibition by atropine in the chicken

PURPOSE

While low-dose atropine eye drops are currently widely used to inhibit myopia development in children, the underlying mechanisms are poorly understood. Therefore, we studied possible retinal mechanisms and receptors that are potentially involved in myopia inhibition by atropine.

METHODS

A total of 250 μg atropine were intravitreally injected into one eye of 19 chickens, while the fellow eyes received saline and served as controls. After 1 h, 1.5 h, 2 h, 3 h, and 4 h, eyes were prepared for vitreal dopamine (DA) measurements, using high-pressure liquid chromatography with electrochemical detection. Twenty-four animals were kept either in bright light (8500 lx) or standard light (500 lx) after atropine injection for 1.5 h before DA was measured. In 10 chickens, the α_2A-adrenoreceptor (α_2A-ADR) agonists brimonidine and clonidine were intravitreally injected into one eye, the fellow eye served as control, and vitreal DA content was measured after 1.5 h. In 6 chickens, immunohistochemical analyses were performed 1.5 h after atropine injection.

RESULTS

Vitreal DA levels increased after a single intravitreal atropine injection, with a peak difference between both eyes after 1.97 h. DA was also enhanced in fellow eyes, suggesting a systemic action of intravitreally administered atropine. Bright light and atropine (which both inhibit myopia) had additive effects on DA release. Quantitative immunolabelling showed that atropine heavily stimulated retinal activity markers ZENK and c-Fos in cells of the inner nuclear layer. Since atropine was recently found to also bind to α_2A-ADRs at doses where it can inhibit myopia, their retinal localization was studied. In amacrine cells, α_2A-ADRs were colocalized with tyrosine hydroxylase (TH), glucagon, and nitric oxide synthase, peptides known to play a role in myopia development in chickens. Intravitreal atropine injection reduced the number of neurons that were double-labelled for TH and α_2A-ADR. α_2A-ADR agonists clonidine and brimonidine (which were also found by other authors to inhibit myopia) severely reduced vitreal DA content in both injected and fellow eyes, compared to eyes of untreated chicks.

CONCLUSIONS

Merging our results with published data, it can be concluded that both muscarinic and α_2A-adrenergic receptors are expressed on dopaminergic neurons and both atropine and α_2A-ADR antagonists stimulate DA release whereas α_2A-ADR agonists strongly suppress its release. Stimulation of DA by atropine was enhanced by bright light. Results are in line with the hypothesis that inhibition of deprivation myopia is correlated with DA stimulation, as long as no toxicity is involved.

Effects of Monocular Atropinization on Refractive Error and Eye Growth in Infant New World Monkeys

Purpose

To explore the effect of topical atropine on axial eye growth and emmetropization in infant marmosets.

Methods

Atropine was applied to one eye from the age of 7 to 56 days in two dose regimens, High (0.1-1% twice daily, increasing with age) or moderate (Mod) (0.1% once daily). Both eyes of the marmosets were refracted, and axial dimensions were measured ultrasonically, at 14, 28, 42, 49, 56, 70, 105, 168, and 279 days of age. The time course of each measured variable was analyzed using multilevel mixed-effects modeling realized in R.

Results

The logistic growth curves fitted to anterior segment depth (ASD) did not differ significantly between the dose regimens, but xmid, the age at which growth was half-maximal, and scal, the time constant of the exponential term in the logistic growth curve equation, differed significantly between the ASD of atropinized and untreated eyes (P = 0.03 and P < 0.0001, respectively), with the ASD of atropinized eyes shorter than that of untreated eyes. The splines fitted to lens thickness did not vary significantly with dose, but differed significantly (P < 0.0001) between the atropinized and untreated eyes, with the atropinized lenses thicker. Vitreous chamber depth (VCD) was not significantly different, but the variance of VCD was significantly greater (P < 0.001) in the atropinized compared with the untreated eyes. Refractive error (RE) became relatively myopic in atropinized eyes. The variance of RE in atropinized eyes was significantly greater (P < 0.0001) than in untreated eyes.

Conclusions

Atropine caused the infant marmoset lens to move forward and thicken, a relative myopia, and increases in the between-animals variance in VCD, which could be considered a failure of emmetropization.

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.

Efficacy of atropine 0.01% for the treatment of childhood myopia in European patients

PURPOSE

To evaluate the efficacy and safety of atropine 0.01% in slowing myopia progression in European paediatric patients.

METHODS

Retrospective, medical records review study. Medical charts of paediatric patients with a myopia progression > 0.5 D/year treated with atropine 0.01% for at least 1 year were included. Patients receive a complete ophthalmic examination before and 12 months after initiation of atropine treatment. A group of myopic untreated children serves as a control group. The rate of myopia progression at baseline and 12 months after treatment with atropine was evaluated. The rate of myopia progression in treated and untreated patients was also compared. Adverse events were recorded.

RESULTS

Medical records of 52 treated and 50 control subjects were analysed. In the atropine group, the mean rate of myopia progression after 12 months of treatment (-0.54 ± 0.61 D) was significantly slower compared with the baseline progression (-1.20 ± 0.64 D; p < 0.0001) and to the progression in the control group (-1.09 ± 0.64; p < 0.0001). The responders patients were 41/52 (79%), whereas 11/52 patients (21%) showed a progression > 0.50 D despite treatment. The only adverse event was temporary photophobia in five patients (9.6%), severe adverse events were not reported, and none of the patients discontinued the treatment.

CONCLUSION

Low-dose atropine significantly slowed the rate of myopia progression in European paediatric patients with a favourable safety profile.

Pharmacogenomic Approach to Antimyopia Drug Development: Pathways Lead the Way

Myopia is the most common eye disorder in the world which is caused by a mismatch between the optical power of the eye and its excessively long axial length. Recent studies revealed that the regulation of the axial length of the eye occurs via a complex signaling cascade, which originates in the retina and propagates across all ocular tissues to the sclera. The complexity of this regulatory cascade has made it particularly difficult to develop effective antimyopia drugs. The current pharmacological treatment options for myopia are limited to atropine and 7-methylxanthine, which have either significant adverse effects or low efficacy. In this review, we focus on the recent advances in genome-wide studies of the signaling pathways underlying myopia development and discuss the potential of systems genetics and pharmacogenomic approaches for the development of antimyopia drugs.

Short-Term Effect of Low-Dose Atropine and Hyperopic Defocus on Choroidal Thickness and Axial Length in Young Myopic Adults

Purpose

To examine the interaction between a short period of hyperopic defocus and low-dose atropine upon the choroidal thickness and ocular biometrics of healthy myopic subjects.

Methods

Twenty young adult myopic subjects had subfoveal choroidal thickness (ChT) and ocular biometry measurements taken before and 30 and 60 min following the introduction of optical blur (0.00 D and −3.00 D) combined with administration of 0.01% atropine or placebo. Each combination of optical blur and drug was tested on different days in a fixed order.

Results

The choroid exhibited significant thinning after imposing hyperopic defocus combined with placebo (mean change of −11 ± 2 μm, p < 0.001). The combination of hyperopic blur and 0.01% atropine led to a significantly smaller magnitude of subfoveal choroidal thinning (−4 ± 8 μm), compared to placebo and hyperopic defocus (p < 0.01). Eyes treated with 0.01% atropine with no defocus exhibited a significant increase in ChT (+6 ± 2 μm, p < 0.01). Axial length also underwent small but significant changes after treatment with hyperopic blur and placebo and 0.01% atropine alone (both p < 0.01), but of opposite direction to the changes in choroidal thickness. However, the 0.01% atropine/hyperopic blur condition did not lead to a significant change in axial length compared to baseline (p > 0.05).

Conclusion

Low-dose atropine does inhibit the short-term effect of hyperopic blur on choroidal thickness and, when used alone, does cause a slight thickening of the choroid in young healthy myopic adults.

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.

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.

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.

Prevention of Progression in Myopia: A Systematic Review

The prevalence of myopia has increased worldwide in recent decades and now is endemic over the entire industrial world. This increase is mainly caused by changes in lifestyle and behavior. In particular, the amount of outdoor activities and near work would display an important role in the pathogenesis of the disease. Several strategies have been reported as effective. Spectacles and contact lenses have shown only slight results in the prevention of myopia and similarly ortokerathology should not be considered as a first-line strategy, given the high risk of infectious keratitis and the relatively low compliance for the patients. Thus, to date, atropine ophthalmic drops seem to be the most effective treatment for slowing the progression of myopia, although the exact mechanism of the effect of treatment is still uncertain. In particular, low-dose atropine (0.01%) was proven to be an effective and safe treatment in the long term due to the lowest rebound effect with negligible side effects.

[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.