Opposite effects of glucagon and insulin on compensation for spectacle lenses in chicks

Mechanisms of emmetropization and what might go wrong in myopia

Studies in animal models and humans have shown that refractive state is optimized during postnatal development by a closed-loop negative feedback system that uses retinal image defocus as an error signal, a mechanism called emmetropization. The sensor to detect defocus and its sign resides in the retina itself. The retina and/or the retinal pigment epithelium (RPE) presumably releases biochemical messengers to change choroidal thickness and modulate the growth rates of the underlying sclera. A central question arises: if emmetropization operates as a closed-loop system, why does it not stop myopia development? Recent experiments in young human subjects have shown that (1) the emmetropic retina can perfectly distinguish between real positive defocus and simulated defocus, and trigger transient axial eye shortening or elongation, respectively. (2) Strikingly, the myopic retina has reduced ability to inhibit eye growth when positive defocus is imposed. (3) The bi-directional response of the emmetropic retina is elicited with low spatial frequency information below 8 cyc/deg, which makes it unlikely that optical higher-order aberrations play a role. (4) The retinal mechanism for the detection of the sign of defocus involves a comparison of defocus blur in the blue (S-cone) and red end of the spectrum (L + M-cones) but, again, the myopic retina is not responsive, at least not in short-term experiments. This suggests that it cannot fully trigger the inhibitory arm of the emmetropization feedback loop. As a result, with an open feedback loop, myopia development becomes "open-loop".

Augmentation of scleral glycolysis promotes myopia through histone lactylation

Myopia is characterized of maladaptive increases in scleral fibroblast-to-myofibroblast transdifferentiation (FMT). Scleral hypoxia is a significant factor contributing to myopia, but how hypoxia induces myopia is poorly understood. Here, we showed that myopia in mice and guinea pigs was associated with hypoxia-induced increases in key glycolytic enzymes expression and lactate levels in the sclera. Promotion of scleral glycolysis or lactate production induced FMT and myopia; conversely, suppression of glycolysis or lactate production eliminated or inhibited FMT and myopia. Mechanistically, increasing scleral glycolysis-lactate levels promoted FMT and myopia via H3K18la, and this promoted Notch1 expression. Genetic analyses identified a significant enrichment of two genes encoding glycolytic enzymes, ENO2 and TPI1. Moreover, increasing sugar intake in guinea pigs not only induced myopia but also enhanced the response to myopia induction via the scleral glycolysis-lactate-histone lactylation pathway. Collectively, we suggest that scleral glycolysis contributes to myopia by promoting FMT via lactate-induced histone lactylation.

Glucagon Increases Retinal Rod Bipolar Cell Inhibition Through a D1 Dopamine Receptor-Dependent Pathway That Is Altered After Lens-Defocus Treatment in Mice

Purpose

Members of the secretin/glucagon family have diverse roles in retinal physiological and pathological conditions. Out of them, glucagon has been associated with eye growth regulation and image defocus signaling in the eye, both processes central in myopia induction. On the other hand, dopamine is perhaps the most studied molecule in myopia and has been proposed as fundamental in myopia pathogenesis. However, glucagonergic activity in the mammalian retina and its possible link with dopaminergic signaling remain unknown.

Methods

To corroborate whether glucagon and dopamine participate together in the modulation of synaptic activity in the retina, inhibitory post-synaptic currents were measured in rod bipolar cells from retinal slices of wild type and negative lens-exposed mice, using whole cell patch-clamp recordings and selective pharmacology.

Results

Glucagon produced an increase of inhibitory post-synaptic current frequency in rod bipolar cells, which was also dependent on dopaminergic activity, as it was abolished by dopamine type 1 receptor antagonism and under scotopic conditions. The effect was also abolished after 3-week negative lens-exposure but could be recovered using dopamine type 1 receptor agonism.

Conclusions

Altogether, these results support a possible neuromodulatory role of glucagon in the retina of mammals as part of a dopaminergic activity-dependent synaptic pathway that is affected under myopia-inducing conditions.

Emmetropization and nonmyopic eye growth

Most eyes start with a hypermetropic refractive error at birth, but the growth rates of the ocular components, guided by visual cues, will slow in such a way that this refractive error decreases during the first 2 years of life. Once reaching its target, the eye enters a period of stable refractive error as it continues to grow by balancing the loss in corneal and lens power with the axial elongation. Although these basic ideas were first proposed over a century ago by Straub, the exact details on the controlling mechanism and the growth process remained elusive. Thanks to the observations collected in the last 40 years in both animals and humans, we are now beginning to get an understanding how environmental and behavioral factors stabilize or disrupt ocular growth. We survey these efforts to present what is currently known regarding the regulation of ocular growth rates.

Association between whole-grain intake and myopia in chinese children: a cross-sectional epidemiological study

BACKGROUND

Nutritional status influences the growth and development of the eyes. However, there are few studies on the association between diet, especially whole grains (WG) consumption, and myopia. The study aimed to evaluate the association between WG intake and myopia prevalence among primary school-age children in China.

METHODS

This cross-sectional epidemiological study conducted between November 2019 and December 2019 included 586 children, aged 6-12 years, attending primary school in Binhai district, Tianjin, China. Ophthalmologic examinations and optometric cycloplegic refraction measurements were conducted. Information was collected on known risks and protective factors for myopia and the consumption of WGs, vegetables, and fruits. This association between the probability of myopia and the proportion of WG consumption (WG proportion was calculated as the mean intake from WG sources divided by total grain intake), adjusted for protective and risk factors, was analysed using crude and multivariable logistic regression.

RESULTS

Among the study participants, 226/586 (38.57%) children had myopia in at least one eye. WG intake was inversely correlated with the prevalence of myopia. Furthermore, in the multivariate analysis, WG intake of > 50% was identified as a protective factor against myopia after subsequent adjustment for children's age, sex, parental myopia, near-work activity, screen time, reading and writing habits, visual fatigue, outdoor time, and classroom light environment (all P < 0.05).

CONCLUSION

WG intake (> 50%) was an independent protective factor against myopia. Modifying the form of grains consumed (whole versus refined) could be one of the targets of future public health measures.

Myopia and BMI: a nationwide study of 1.3 million adolescents

OBJECTIVE

This study analyzed the association between adolescent BMI and myopia severity.

METHODS

This cross-sectional study comprised 1,359,153 adolescents who were medically examined before mandatory military service. Mild-to-moderate and high myopia were defined based on right-eye refractive data. BMI was categorized based on the US age- and sex-matched percentiles. Logistic regression models were applied separately for women and men to estimate odds ratios (ORs) for myopia per BMI category.

RESULTS

A total of 318,712 adolescents had mild-to-moderate myopia and 23,569 had high myopia. Compared with low-normal BMI (reference group), adjusted ORs for mild-to-moderate and high myopia increased with increasing BMI status, reaching 1.39 (95% CI: 1.23-1.57) and 1.73 (95% CI: 1.19-2.51) for men with severe obesity, respectively, and 1.19 (95% CI: 1.12-1.27) and 1.38 (95% CI: 1.14-1.65) for women with mild obesity, respectively. ORs for mild-to-moderate and high myopia were also higher in men with underweight (OR = 1.20; 95% CI: 1.18-1.23 and OR = 1.39; 95% CI: 1.30-1.47) and women with underweight (OR = 1.06; 95% CI: 1.03-1.09 and OR = 1.12; 95% CI: 1.04-1.22). The overall size effect was greater for men than women (p_interaction  < 0.001), in whom the group with severe obesity did not reach statistical significance.

CONCLUSIONS

BMI was associated with myopia in a J-shaped pattern, with the size effect being greater for adolescent men than women. This study indicates that both low BMI and high BMI are associated with mild-to-moderate and severe myopia.

The choroid-sclera interface: An ultrastructural study

Emmetropization is an active and visually guided process that involves the retina, choroid and sclera, and results in compensatory changes in eye growth. This guided growth is the result of visual cues and possibly mechanical interactions being translated into growth signals via molecular events from the retina into the choroid and sclera, through the choroidal scleral transition zone. If mechanical interactions were a part of the choroid-sclera signaling transduction cascade, specific morphological arrangements should be detectable in this region at the ultrastructural level. The goal of this study was to investigate the ultrastructural features of the choroidal scleral transition zone by comparing avian, non-human primate and human eyes, with the goal to confirm whether specific mechanical structures are present. Choroidal and scleral tissue from chicken, marmoset, and human eyes were imaged using transmission electron microscopy to document the choroid-sclera transition zone. In chicken eyes, fibroblast lamellae bordered the scleral matrix and formed thin end elongated processes that were undercut by scleral collagen fibrils. These processes back-looped into the scleral matrix, and displayed small club-like membrane protrusions. Differences in these arrangements in mature vs young chickens were not detected. The club-like membrane protrusions identified in chickens were rare in marmoset eyes, which instead exhibited two types of collagen fibrils discriminated by size, and were absent in the human eyes investigated. In marmoset and human eyes, elastic components were detected in the transition zone that were absent in chickens. In summary, cellular/membrane specializations indicating a mechanical interaction at the choroid-sclera transition zone were not detected in chicken, non-human primate or human eyes. If mechanotransduction is necessary for scleral growth, matrix integrity or development, alternative structural arrangements might be required.

The Role of GJD2(Cx36) in Refractive Error Development

Refractive errors are common eye disorders characterized by a mismatch between the focal power of the eye and its axial length. An increased axial length is a common cause of the refractive error myopia (nearsightedness). The substantial increase in myopia prevalence over the last decades has raised public health concerns because myopia can lead to severe ocular complications later in life. Genomewide association studies (GWAS) have made considerable contributions to the understanding of the genetic architecture of refractive errors. Among the hundreds of genetic variants identified, common variants near the gap junction delta-2 (GJD2) gene have consistently been reported as one of the top hits. GJD2 encodes the connexin 36 (Cx36) protein, which forms gap junction channels and is highly expressed in the neural retina. In this review, we provide current evidence that links GJD2(Cx36) to the development of myopia. We summarize the gap junctional communication in the eye and the specific role of GJD2(Cx36) in retinal processing of visual signals. Finally, we discuss the pathways involving dopamine and gap junction phosphorylation and coupling as potential mechanisms that may explain the role of GJD2(Cx36) in refractive error development.

Myopia and Early-Onset Type 2 Diabetes: A Nationwide Cohort Study

CONTEXT

A correlation between myopia and insulin resistance has been suggested.

OBJECTIVE

We investigated the association between myopia in adolescence and type 2 diabetes (T2D) incidence in young adulthood.

METHODS

This population-based, retrospective, cohort study comprised 1 329 705 adolescents (579 543 women, 43.6%) aged 16 to 19 years, who were medically examined before mandatory military service during 1993 to 2012, and whose data were linked to the Israel National Diabetes Registry. Myopia was defined based on right-eye refractive data. Cox proportional models were applied, separately for women and men, to estimate hazard ratios (HRs) for T2D incidence per person-years of follow-up.

RESULTS

There was an interaction between myopia and sex with T2D (P < .001). For women, T2D incidence rates (per 100 000 person-years) were 16.6, 19.2, and 25.1 for those without myopia, and with mild-to-moderate and high myopia, respectively. These corresponded to HRs of 1.29 (95% CI, 1.14-1.45) and 1.63 (1.21-2.18) for women with mild-to-moderate and high myopia, respectively, compared to those without myopia, after adjustment for age at study entry, birth year, adolescent body mass index, cognitive performance, socioeconomic status, and immigration status. Results persisted in extensive sensitivity and subgroup analyses. When managed as a continuous variable, every 1-diopter lower spherical equivalent yielded a 6.5% higher adjusted HR for T2D incidence (P = .003). There was no significant association among men.

CONCLUSION

For women, myopia in adolescence was associated with a significantly increased risk for incident T2D in young adulthood, in a severity-dependent manner. This finding may support the role of insulin resistance in myopia pathogenesis.

Association of Myopia With Risk of Incident Metabolic Syndrome: Findings From the UK Biobank Study Cohort of 91,591 Participants

Purpose

To investigate the association between myopia and risk of metabolic syndrome (MetS) in a prospective cohort from the UK Biobank Study.

Methods

Volunteers (aged 40 years and above) free of baseline MetS and cataract included from the UK Biobank Study, a prospective follow-up cohort. Myopia was defined using uncycloplegic autorefraction, self-report-myopia, and medical records for refractive error at baseline. MetS as well as components of MetS were diagnosed based on health records, blood biochemistry, and questionnaires. Questionnaires determined the status of smoking, drinking, physical activity and dietary supplements, as well as ethnicity and education.

Results

A total of 91,591 participants were available in the analysis, with a mean age of 55.37 ± 8.07 years at baseline and a median follow-up years of 11.16 years. The proportion of myopia was 49.7%, and a total of 937 (1.0%) participants were identified as having incident MetS (0.09/100 person years). Subjects with myopia were more likely to have MetS compared with non-myopic subjects (0.82 vs. 0.21%, Log-rank test P < 0.001). Mopes had greater risk of incident MetS (Hazard ratio [HR] = 4.19, 95% confidence interval [CI] 3.57-4.93, P < 0.001) adjusting for baseline age, gender, education and ethnicity. After further controlling for lifestyle factors (smoking, drinking, physical activity, and fish oil supplement) or baseline metabolic disorders, the risk of incident MetS were 3.88- and 4.06-fold greater in myopic subjects than those without myopia, respectively (P < 0.001 for both models). The severity of myopia was not significantly correlated to incident MetS in multivariate-adjusted models.

Conclusions

An increased risk of incident MetS among the elderly is associated with myopia, but not the degree of myopia. These findings highlighted the need of prevention of MetS among older adults with myopia.

Advances in biomedical study of the myopia-related signaling pathways and mechanisms

Myopia has become one of the most critical health problems in the world with the increasing time spent indoors and increasing close work. Pathological myopia may have multiple complications, such as myopic macular degeneration, retinal detachment, cataracts, open-angle glaucoma, and severe cases that can cause blindness. Mounting evidence suggests that the cause of myopia can be attributed to the complex interaction of environmental exposure and genetic susceptibility. An increasing number of researchers have focused on the genetic pathogenesis of myopia in recent years. Scleral remodeling and excessive axial elongating induced retina thinning and even retinal detachment are myopia's most important pathological manifestations. The related signaling pathways are indispensable in myopia occurrence and development, such as dopamine, nitric oxide, TGF-β, HIF-1α, etc. We review the current major and recent progress of biomedicine on myopia-related signaling pathways and mechanisms.

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.

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

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

Nutritional Factors and Myopia: An Analysis of National Health and Nutrition Examination Survey Data

SIGNIFICANCE

The rise in the prevalence of myopia, a significant worldwide public health concern, has been too rapid to be explained by genetic factors alone and thus suggests environmental influences.

PURPOSE

Relatively little attention has been paid to the possible role of nutrition in myopia. The availability of the large National Health and Nutrition Examination Survey data set, which includes results from vision examinations, offers the opportunity to investigate the relationship between several nutrition-related factors, including body metrics, and the presence and magnitude of myopia.

METHODS

Cross-sectional survey data sets with vision examination, demographic, body metrics, and nutritional data, collected as part of the National Health and Nutrition Examination Survey over the years of 2003 to 2008, were extracted for analysis. Based on already published basic and epidemiological studies, the following parameters were selected for study: body height and body mass index, demographics, serum vitamin D and glucose/insulin levels, and caffeine intake, using multivariable models and objectively measured refractive errors as the main outcome measure.

RESULTS

Data from a total of 6855 ethnically diverse Americans aged 12 to 25 years were analyzed. In final multivariate models, female sex and age were the most significant factors related to myopia status and refractive error. In general, body metrics (body mass index) or nutritional factors (serum vitamin D, glucose levels, and caffeine intake) were found to be associated with refractive error or myopia status; however, increased insulin levels were related to increased odds of having myopia.

CONCLUSIONS

These largely negative findings suggest that other environmental factors, such as those related to the visual environment, may contribute more to the development and/or progression of myopia and would argue for continued research in these areas in support of more evidence-based myopia clinical management.

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.

Probability of myopia in children with high refined carbohydrates consumption in France

BACKGROUND

Evaluate risk factors for paediatric myopia in a contemporary French cohort taking into account consumption of refined carbohydrates (starches and sugars).

METHODS

An epidemiological cross-sectional study was conducted between May 2017 and May 2018. Two hundred sixty-four children aged 4 to 18 years attending the Centre Hospitalier Universitaire Gui de Chauliac in Montpellier were recruited. Ophthalmologic or optometric cycloplegic refraction were measured. Evaluated risk factors for myopia were collected, including family history of myopia, outdoor time, reading time, screen time, physical activity, and consumption of refined carbohydrates. Association between the probability of at least one eye showing myopia (defined as < 0 D) and frequency of refined carbohydrates consumption adjusted for risk factors and control factors was tested.

RESULTS

Overall, 86/264 (32.6%) children investigated showed myopia in at least one eye. We included 180 children exhibiting refraction < 3 D in both eyes: 88 (48.9%) girls and 92 (51.1%) boys. The consumption of refined carbohydrates significantly increased the probability of myopia for girls (odds ratio [OR] = 1.07; 95% confidence interval [CI], 1.02-1.13; P = 0.009) but decreased it for boys (OR = 0.94; 95% CI, 0.89-0.98; P = 0.011). The probability of myopia was marginally increased with increased screen time (OR = 2.32; 95% CI, 0.94-6.47; P = 0.083). Outdoor time seemed marginally protective (OR = 0.74; 95% CI, 0.54-1.01; P = 0.057).

CONCLUSION

Refined carbohydrates consumption could be associated with child myopia, with increased probability for girls and unexpected reduced probability for boys, possibly due to the fact that frequency of carbohydrates consumption do not really capture boy's chronic hyperglycemia, boys being more physically active than girls at all ages. Some known risk/protective factors of myopia were marginally significant: screen time (risk) and outdoor time (protective). This study reinforces the belief that modifiable risk factors for myopia could be targets for future public health actions.

DNA methylation and mRNA expression of IGF-1 and MMP-2 after form-deprivation myopia in guinea pigs

PURPOSE

The molecular mechanism of form-deprivation myopia is unclear. This study was aimed to investigate the roles of scleral DNA methylation and mRNA expression of IGF-1 and MMP-2 in a guinea pig model of form-deprivation myopia.

METHODS

Seventy 2-week-old male guinea pigs were assigned to three groups: (1) zero week group that was used to collect baseline data; (2) monocular deprivation treatment (MDT) group, in which a thin slice of opaque latex glove was placed over the right eyes of the animals for four weeks, and the left eyes were untreated and served as the monocular contralateral control (MCC) group; (3) control group (CG), in which the animals grew four weeks, but received no manipulation. Animals in each group were evenly divided for DNA methylation assay and quantitative PCR (qPCR). After eye enucleation, the sclerae were harvested for DNA methylation assay and qPCR. The DNA methylation pattern in the promoter and exon regions of IGF-1 and MMP-2, along with the mRNA expression level of them, were determined by base-specific cleavage and mass spectrometry and qPCR, respectively.

RESULTS

After four weeks of form-deprivation, DNA methylation at 4/8 cytosine-guanine sites in the IGF-1 promoter was significantly lower in the MDT eyes than in the MCC or CG eyes. In addition, the level of IGF-1 mRNA was moderately higher in MDT eyes compared to the MCC eyes and CG eyes. DNA methylation at 4/14 cytosine-guanine sites in the MMP-2 gene was very low, and no significant change was observed between the MDT eyes and the MCC or CG ones. However, the level of MMP-2 mRNA in MDT eyes was significant higher compared with MCC eyes and CG eyes, with an increase of 217% and 222%, respectively.

CONCLUSIONS

In our guinea pig model of form-deprivation myopia, the methylation of four cytosine-guanine sites in the IGF-1 gene promoter was significantly lower in the sclera after four weeks of MDT, and the transcription level of scleral IGF-1 was moderately higher. Hence, the IGF-1 gene methylation might play a role in the pathogenesis of form-deprivation myopia in guinea pigs. The level of MMP-2 mRNA in the sclera of MDT eyes was significantly higher, but not regulated by the methylation pathway, as the methylation status of MMP-2 was unchanged.

Change in peripapillary and macular choroidal thickness change in children with type 1 diabetes mellitus without visual impairment or diabetic retinopathy

PURPOSE

To study the characteristics of choroid thickness (CT) of the optic disc and macula in children with type 1 diabetes mellitus (T1DM) without visual impairment and diabetic retinopathy (DR) and analyse associated factors.

METHODS

A square area of 6 × 6 mm around the centre of the optic disc and macula was scanned. The indices analysed mainly included CT at the macular centre (1 mm), and temporal, superior, nasal or inferior aspect of the inner ring (1-3 mm) and outer ring of (3-6 mm) optic disc and macula. Independent risk factors were analysed using multifactor linear regression.

RESULTS

A total of 44 children with T1DM and 48 healthy subjects were enrolled. The diabetic group showed significant increase in the inferior inner ring of parapapillary CT (100.99 ± 30.42 μm versus 89.41 ± 34.00 μm, p = 0.04) and nasal outer ring of parapapillary CT (157.02 ± 47.35 μm versus 131.15 ± 35.17 μm, p = 0.01) as compared to those values in the healthy controls. Spherical equivalent refraction and family history of hypertension are independent factors of both peripappillary choroid thickness (PPCT) and macular choroid thickness (PMCT). Spherical equivalent refraction (p = 0.01) and serum cholesterol (p = 0.03) were independent factors of the inferior inner ring of parapapillary CT, whereas family history of hypertension was an independent factor of the nasal outer ring of parapapillary CT (p = 0.001).

CONCLUSION

In children with diabetes without DR or visual impairment, the CT increase in nasal outer ring of parapapillary (PPNO) and the inferior inner ring of parapapillary (PPII) may be the characteristic pre-DR alteration at the early stage of DM. For children with higher serum cholesterol and family history of hypertension, the change of the nasal outer ring of parapapillary CT and the inferior inner ring of parapapillary CT may be more advanced.

Subfoveal choroidal thickness at age 9 years in relation to clinical and perinatal characteristics in the population-based Generation R Study

PURPOSE

To assess the association between clinical and perinatal characteristics and subfoveal choroidal thickness in 9-year-old children.

METHODS

The study included data from the population-based Generation R cohort, whose participants underwent cycloplegic refractometry, ocular biometry, height, weight and subfoveal choroidal thickness measurements using a swept-source optical coherence tomography (SS-OCT) instrument. Birth parameters were obtained using medical records. Statistical analyses were performed using multivariate regression models adjusted for age, ethnicity and sex.

RESULTS

A total of 1018 children (52.5% girls, 47.5% boys) with a mean age of 9.9 ± 0.3 years and a mean cycloplegic spherical equivalent refraction of 0.80 ± 1.1 D in boys and 0.81 ± 1.4 in girls were eligible for analysis. The subfoveal choroid was 17 μm thicker in girls (298 ± 60.6 μm) than in boys (281 ± 55.0 μm; p < 0.001), a difference of 9.1 μm persisting after adjustment for age, ethnicity and axial length (p = 0.017). Subfoveal choroidal thickness decreased with increasing ocular axial length (-16.2 μm/mm, 95% CI -21.2 to -12.4, p < 0.001) and with increasing myopic refraction (-10.0 μm/D, 95% CI 6.8-13.1; p < 0.001, adjusted for age, ethnicity, axial length and sex) while it increased with increasing body height (1.3 μm/cm, 95% CI 0.8 to 1.9, p < 0.001). Additionally, choroidal thickness increased with increasing birthweight (13.0 μm/kg; 95% CI 0.006-0.020; p < 0.001) and increasing size for gestational age (8.2 μm/kg; 95% CI 4.6-11.8; p < 0.001). Smoking up until the time that pregnancy became known was associated with a thinner choroid (p = 0.016). There was no detectable effect of alcohol consumption. The distributions of axial length, refraction and choroidal thickness were narrower than in older populations.

CONCLUSION

The subfoveal choroid was thicker in girls than in boys, and higher body height, higher birthweight and larger size for gestational age were associated with a thicker subfoveal choroid. The implications of these findings for myopia development need further evaluation in longitudinal studies.

Alteration of retinal metabolism and oxidative stress may implicate myopic eye growth: Evidence from discovery and targeted proteomics in an animal model

Myopia, the most common cause of impaired vision, may induce sight- threatening diseases or ocular complications due to axial elongation. The exact mechanisms underlying myopia development have received much attention and understanding of these is necessary for clinical prevention or therapeutics. In this study, quantitative proteomics using Isotope Coded Protein Label (ICPL) was applied to identify differentially regulated proteins in the retinas of myopic chicks and, from their presence, infer the possible pathogenesis of excessive ocular elongation. Newly hatched white leghorn chicks (n = 15) wore -10D and + 10D lenses bilaterally for 3 and 7 days, respectively, to develop progressive lens-induced myopia (LIM) and hyperopia (LIH). Retinal proteins were quantified with nano-liquid chromatography electrospray ionization coupled with tandem mass spectrometry (nanoLC-ESI-MS/MS). Bioinformatics analysis of differentially regulated proteins revealed that the majority originated from the cytoplasmic region and were related to various metabolic, glycolytic, or oxidative processes. The fold changes of four proteins of interest (vimentin, apolipoprotein A1, interphotoreceptor retinoid binding protein, and glutathione S-transferase) were further confirmed by a novel high-resolution multiple reaction monitoring mass spectrometry (MRM-HR) using a label-free approach. SIGNIFICANCE: Discovery of effective protein biomarkers of myopia has been extensively studied to inhibit myopia progression. This study first applied lens-induced hyperopia and myopia in the same chick to maximize the inter-ocular differences, aiming to discover more protein biomarker candidates. The findings provided new evidence that myopia was metabolism related, accompanied by altered energy generation and oxidative stress at retinal protein levels. The results in the retina were also compared to our previous study in vitreous using ICPL quantitative technology. We have now presented the protein changes in these two adjacent tissues, which may provide extra information of protein changes during ocular growth in myopia.

Association of IGF1 single-nucleotide polymorphisms with myopia in Chinese children

Purpose

To investigate the association between insulin-like growth factor 1 (IGF1) single-nucleotide polymorphisms (SNPs) and myopia in a young Chinese population.

Methods

A total of 654 Chinese children aged 6–13 years from one primary school participated in our study and underwent a series of comprehensive ocular examinations, including cycloplegic refraction and measurements of axial length. Myopia was defined as a spherical equivalence (SE) ≤ −0.5 D in the worse eye. In total, six tagging SNPs of IGF1 were genotyped using the PCR-LDR (Polymerase Chain Reaction-Ligation Detection Reaction) method. We tested four different genetic modes (the allele, dominant, recessive, and additive models) of these SNPs and used multivariate logistic regression to calculate the effect of SNPs on myopia. In addition, we conducted a haplotype analysis with a variable-sized slide-window strategy.

Results

Overall, 281 myopic children and 373 non-myopic controls were included in the analysis. The SNP rs2162679 showed a statistical difference between the two groups in both the allele (p = 0.0474) and additive (p = 0.0497) models. After adjusting for age and gender, children with the genotype AA in the SNP rs2162679 had a higher risk of myopia than those with the genotype GG (OR = 2.219, 95% CI [1.218–4.039], p = 0.009). All haplotypes that varied significantly between the two groups contained the SNP rs2162679, and the four-SNP window rs5742653–rs2162679 had the lowest p value (Chi square = 5.768, p = 0.0163). However, after permutation tests, none of the associations remained statistically significant.

Conclusion

The SNP rs2162679 in IGF1 was associated with myopia in a young Chinese population. The G allele in the SNP rs2162679 may protect against myopia.

IMI - Report on Experimental Models of Emmetropization and Myopia

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

The Adenosine Receptor Antagonist, 7-Methylxanthine, Alters Emmetropizing Responses in Infant Macaques

Purpose

Previous studies suggest that the adenosine receptor antagonist, 7-methylxanthine (7-MX), retards myopia progression. Our aim was to determine whether 7-MX alters the compensating refractive changes produced by defocus in rhesus monkeys.

Methods

Starting at age 3 weeks, monkeys were reared with −3 diopter (D; n = 10; 7-MX −3D/pl) or +3D (n = 6; 7-MX +3D/pl) spectacles over their treated eyes and zero-powered lenses over their fellow eyes. In addition, they were given 100 mg/kg of 7-MX orally twice daily throughout the lens-rearing period (age 147 ± 4 days). Comparison data were obtained from lens-reared controls (−3D/pl, n = 17; +3D/pl, n = 9) and normal monkeys (n = 37) maintained on a standard diet. Refractive status, corneal power, and axial dimensions were assessed biweekly.

Results

The −3D/pl and +3D/pl lens-reared controls developed compensating myopic (−2.10 ± 1.07 D) and hyperopic anisometropias (+1.86 ± 0.54 D), respectively. While the 7-MX +3D/pl monkeys developed hyperopic anisometropias (+1.79 ± 1.11 D) that were similar to those observed in +3D/pl controls, the 7-MX −3D/pl animals did not consistently exhibit compensating myopia in their treated eyes and were on average isometropic (+0.35 ± 1.96 D). The median refractive errors for both eyes of the 7-MX −3D/pl (+5.47 D and +4.38 D) and 7-MX +3D/pl (+5.28 and +3.84 D) monkeys were significantly more hyperopic than that for normal monkeys (+2.47 D). These 7-MX–induced hyperopic ametropias were associated with shorter vitreous chambers and thicker choroids.

Conclusions

In primates, 7-MX reduced the axial myopia produced by hyperopic defocus, augmented hyperopic shifts in response to myopic defocus, and induced hyperopia in control eyes. The results suggest that 7-MX has therapeutic potential in efforts to slow myopia progression.

Novel evidence for complement system activation in chick myopia and hyperopia models: a meta-analysis of transcriptome datasets

Myopia (short-sightedness) and hyperopia (long-sightedness) occur when the eye grows too long or short, respectively, for its refractive power. There are currently approximately 1.45 billion myopes worldwide and prevalence is rising dramatically. Although high myopia significantly increases the risk of developing a range of sight-threatening disorders, the molecular mechanisms underlying ocular growth regulation and its relationship to these secondary complications remain poorly understood. Thus, this study meta-analyzed transcriptome datasets collected in the commonly used chick model of optically-induced refractive error. Fifteen datasets (collected across five previous studies) were obtained from GEO, preprocessed in Bioconductor, and divided into 4 conditions representing early (≤1 day) and late (>1 day) myopia and hyperopia induction. Differentially expressed genes in each condition were then identified using Rank Product meta-analysis. The results provide novel evidence for transcriptional activation of the complement system during both myopia and hyperopia induction, and confirm existing literature implicating cell signaling, mitochondrial, and structural processes in refractive error. Further comparisons demonstrated that the meta-analysis results also significantly improve concordance with broader omics data types (i.e., human genetic association and animal proteomics studies) relative to previous transcriptome studies, and show extensive similarities with the genes linked to age-related macular degeneration, choroidal neovascularization, and cataract.

Altered Refractive Development in Mice With Reduced Levels of Retinal Dopamine

Purpose

The neuromodulator dopamine (DA) has been implicated in the prevention of excessive ocular elongation and myopia in various animal models. This study used retina-specific DA knockout mice to investigate the role of retinal DA in refractive development and susceptibility to experimental myopia.

Methods

Measurements of refractive error, corneal curvature, and ocular biometrics were obtained as a function of age for both untreated and form-deprived (FD) groups of retina-specific tyrosine hydroxylase knockout (rTHKO) and control (Ctrl) mice. Retinas from each group were analyzed by HPLC for levels of DA and its primary metabolite (DOPAC).

Results

Under normal visual conditions, rTHKO mice showed significantly myopic refractions (F(1,188) = 7.602, P < 0.001) and steeper corneas (main effect of genotype F(1,180) = 5.1, P < 0.01) at 4 and 6 weeks of age compared with Ctrl mice. Retina-specific THKO mice also had thinner corneas (main effect of genotype F(1,181) = 37.17, P < 0.001), thinner retinas (F(6,181) = 6.07, P < 0.001), and shorter axial lengths (F(6,181) = 3.78, P < 0.01) than Ctrl mice. Retina-specific THKO retinas contained less than 15% of DA and DOPAC compared with Ctrl retinas, and the remaining DA had a significantly higher turnover, as indicated by DOPAC/DA ratios (Student's t-test, P < 0.05). Retina-specific THKO mice showed similar, yet more variable, responses to 6 weeks of FD compared with Ctrl mice.

Conclusions

Diminished retinal DA induced spontaneous myopia in mice raised under laboratory conditions without form deprivation. The relative myopic shift in rTHKO mice may be explained by steeper corneas, an unexpected finding. The chronic loss of DA did not significantly alter the FD myopia response in rTHKO mice.

Association of Insulin-Like Growth Factor-1 Gene Polymorphisms with Different Types of Myopia in Egyptian Patients

AIMS

To investigate the effect of the insulin-like growth factor-1 (IGF-1) gene's rs6214 and rs5742632 polymorphisms on IGF-1 expression levels and their association with different types of myopia in Egyptian patients.

METHODS

A case-control format was used that included 272 patients with myopia and 136 controls. The IGF-1 gene rs6214 and rs5742632 polymorphisms were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analyses. IGF-1 levels were measured by an enzyme-linked immunosorbent assay.

RESULTS

In patients with high-grade myopia, the frequencies of the IGF-1 rs6214 GA and AA genotypes, and the A allele were significantly increased compared to the control group: 41.9% vs. 33.8%, 17.7% vs. 8.9%, and 38.9% vs. 25.7%, respectively. Subjects with the GA and AA genotypes and carriers of A allele were significantly more likely to have high-grade myopia: odds ratios (OR) = 1.75, 95% confidence interval (CI) = 1.03-2.9, and p = 0.03; OR = 2.8, 95% CI = 1.3-6.0, and p = 0.003; and OR = 1.8, 95% CI = 1.25-2.61, and p = 0.001, respectively. A nonsignificant association of the IGF-1 gene rs5742632 polymorphism with the two myopia groups was also observed. The IGF-1 levels were significantly increased in patients with high-grade myopia and simple myopia compared to the control group (p < 0.05). In addition, our results showed a nonsignificant association of the IGF-1 (rs6214-rs5742632) haplotype with either simple myopia or high-grade myopia.

CONCLUSIONS

We found a significant association of the IGF-1 gene rs6214 polymorphism in Egyptian patients with simple myopia and high-grade myopia. IGF-1 levels were significantly increased in relation to the IGF-1 rs6214 genotypes, while a nonsignificant association was found between IGF-1 level and the IGF-1 (rs5742632) genotypes.

Is myopia another clinical manifestation of insulin resistance?

Myopia is a multifactorial visual refraction disease, in which the light rays from distant objects are focused in front of retina, causing blurry vision. Myopic eyes are characterized by an increased corneal curvature and/or ocular axial length. The prevalence of myopia has increased in recent decades, a trend that cannot be attributed exclusively to genetic factors. Low and middle income countries have a higher burden of refractive error, which we propose could be a consequence of a shorter exposure time to a westernized lifestyle, a phenomenon that may also explain the rapid increase in cardiometabolic diseases, such as diabetes, among those populations. We suggest that interactions between genetic, epigenetic and a rapidly changing environment are also involved in myopia onset and progression. Furthermore, we discuss several possible mechanisms by which insulin resistance may promote abnormal ocular growth and myopia to support the hypothesis that insulin resistance and hyperinsulinemia are involved in its pathogenesis, providing a link between trends in myopia and those of cardiometabolic diseases. There is evidence that insulin have direct ocular growth promoting effects as well an indirect effect via the induction of insulin-like growth factors leading to decreases insulin-like growth factor-binding protein, also implicated in ocular growth.

The effect of intravitreal injection of vehicle solutions on form deprivation myopia in tree shrews

lntravitreal injection of substances dissolved in a vehicle solution is a common tool used to assess retinal function. We examined the effect of injection procedures (three groups) and vehicle solutions (four groups) on the development of form deprivation myopia (FDM) in juvenile tree shrews, mammals closely related to primates, starting at 24 days of visual experience (about 45 days of age). In seven groups (n = 7 per group), the myopia produced by monocular form deprivation (FD) was measured daily for 12 days during an 11-day treatment period. The FD eye was randomly selected; the contralateral eye served as an untreated control. The refractive state of both eyes was measured daily, starting just before FD began (day 1); axial component dimensions were measured on day 1 and after eleven days of treatment (day 12). Procedure groups: the myopia (treated eye - control eye refraction) in the FD group was the reference. The sham group only underwent brief daily anesthesia and opening of the conjunctiva to expose the sclera. The puncture group, in addition, had a pipette inserted daily into the vitreous. In four vehicle groups, 5 μL of vehicle was injected daily. The NaCl group received 0.85% NaCl. In the NaCl + ascorbic acid group, 1 mg/mL of ascorbic acid was added. The water group received sterile water. The water + ascorbic acid group received water with ascorbic acid (1 mg/mL). We found that the procedures associated with intravitreal injections (anesthesia, opening of the conjunctiva, and puncture of the sclera) did not significantly affect the development of FDM. However, injecting 5 μL of any of the four vehicle solutions slowed the development of FDM. NaCl had a small effect; myopia development in the last 6 days (-0.15 ± 0.08 D/day) was significantly less than in the FD group (-0.55 ± 0.06 D/day). NaCl + Ascorbic acid further slowed the development of FDM on several treatment days. H2O (-0.09 ± 0.05 D/day) and H2O + ascorbic acid (-0.08 ± 0.05 D/day) both almost completely blocked myopia development. The treated eye vitreous chamber elongation, compared with the control eye, in all groups was consistent with the amount of myopia. When FD continued (days 12-16) without injections in the water and water + ascorbic acid groups, the rate of myopia development quickly increased. Thus, it appears the vehicles affected retinal signaling rather than causing damage. The effect of water and water + ascorbic acid may be due to reduced osmolality or ionic concentration near the tip of the injection pipette. The effect of ascorbic acid, compared to NaCl alone, may be due to its reported dopaminergic activity.

Heparin-binding EGF-like growth factor (HB-EGF) stimulates the proliferation of Müller glia-derived progenitor cells in avian and murine retinas

Müller glia can be stimulated to de-differentiate, proliferate and form Müller glia-derived progenitor cells (MGPCs) that regenerate retinal neurons. In the zebrafish retina, heparin-binding EGF-like growth factor (HB-EGF) may be one of the key factors that stimulate the formation of proliferating MGPCs. Currently nothing is known about the influence of HB-EGF on the proliferative potential of Müller glia in retinas of birds and rodents. In the chick retina, we found that levels of both hb-egf and egf-receptor are rapidly and transiently up-regulated following NMDA-induced damage. Although intraocular injections of HB-EGF failed to stimulate cell-signaling or proliferation of Müller glia in normal retinas, HB-EGF stimulated proliferation of MGPCs in damaged retinas. By comparison, inhibition of the EGF-receptor (EGFR) decreased the proliferation of MGPCs in damaged retinas. HB-EGF failed to act synergistically with FGF2 to stimulate the formation of MGPCs in the undamaged retina and inhibition of EGF-receptor did not suppress FGF2-mediated formation of MGPCs. In the mouse retina, HB-EGF stimulated the proliferation of Müller glia following NMDA-induced damage. Furthermore, HB-EGF not only stimulated MAPK-signaling in Müller glia/MGPCs, but also activated mTor- and Jak/Stat-signaling. We propose that levels of expression of EGFR are rate-limiting to the responses of Müller glia to HB-EGF and the expression of EGFR can be induced by retinal damage, but not by FGF2-treatment. We conclude that HB-EGF is mitogenic to Müller glia in both chick and mouse retinas, and HB-EGF is an important player in the formation of MGPCs in damaged retinas.

RPE and Choroid Mechanisms Underlying Ocular Growth and Myopia

Myopia is the most common type of refractive errors and one of the world's leading causes of blindness. Visual manipulations in animal models have provided convincing evidence for the role of environmental factors in myopia development. These models along with in vitro studies have provided important insights into underlying mechanisms. The key locations of the retinal pigment epithelium (RPE) and choroid make them plausible conduits for relaying growth regulatory signals originating in the retina to the sclera, which ultimately determines eye size and shape. Identifying the key signal molecules and their targets may lead to the development of new myopia control treatments. This section summarizes findings implicating the RPE and choroid in myopia development. For RPE and/or choroid, changes in morphology, activity of ion channels/transporters, as well as in gene and protein expression, have been linked to altered eye growth. Both tissues thus represent potential targets for novel therapies for myopia.

The association between IGF-1 polymorphisms and high myopia

The potential association between IGF-1 polymorphisms and high myopia has been investigated in previous studies, but the actual relationship remains controversial. Accordingly, we conducted a meta-analysisincludingcase-control and cohort studies to assess the existing relationship between high myopia and IGF-1 polymorphisms. We searched MEDLINE, EMBASE, and OVID. Odds ratios (OR) with 95% confidence intervals (CI) were derived for single-nucleotide polymorphisms (SNPs) involved in the studies obtained from the retrospective database search. Analyses of heterogeneity, sensitivity, and publication bias were also conducted. The findings from this meta-analysis were based on approximately 2,187 high myopia cases and 1,183 controls, and were used to assess the association between three IGF-1 genetic polymorphisms (rs6214, rs12423791, and rs5742632) and high myopia risks. We investigated the association of the IGF-1 gene SNP rs6214, but no statistical association was observed in the resulting odds ratios (OR) in the allelic (OR = 1.06, 95% CI = 0.89-1.25), dominant (OR = 1.07, 95% CI = 0.90-1.27), or recessive models (OR = 1.06, 95% CI = 0.89-1.26), or in the homozygote (OR = 1.12, 95% CI = 0.91-1.38) and heterozygote comparisons (OR = 1.06, 95% CI = 0.88-1.27). Simultaneously, two other selected SNPs, rs12423791 and rs5742632, were also studied, but similarly, no statistical association existed between these polymorphisms and the risk of high myopia. In conclusions, no statistical association between IGF-1 polymorphisms (rs6214, rs12423791, and rs5742632) and the risk of high myopia was observed following the reported meta-analysis.

The dynamic sclera: extracellular matrix remodeling in normal ocular growth and myopia development

Myopia is a common ocular condition, characterized by excessive elongation of the ocular globe. The prevalence of myopia continues to increase, particularly among highly educated groups, now exceeding 80% in some groups. In parallel with the increased prevalence of myopia, are increases in associated blinding ocular conditions including glaucoma, retinal detachment and macular degeneration, making myopia a significant global health concern. The elongation of the eye is closely related to the biomechanical properties of the sclera, which in turn are largely dependent on the composition of the scleral extracellular matrix. Therefore an understanding of the cellular and extracellular events involved in the regulation of scleral growth and remodeling during childhood and young adulthood will provide future avenues for the treatment of myopia and its associated ocular complications.

Pharmaceutical intervention for myopia control

Myopia is the result of a mismatch between the optical power and the length of the eye, with the latter being too long. Driving the research in this field is the need to develop myopia treatments that can limit axial elongation. When axial elongation is excessive, as in high myopia, there is an increased risk of visual impairment and blindness due to ensuing pathologies such as retinal detachments. This article covers both clinical studies involving myopic children, and studies involving animal models for myopia. Atropine, a nonselective muscarinic antagonist, has been studied most extensively in both contexts. Because it remains the only drug used in a clinical setting, it is a major focus of the first part of this article, which also covers the many shortcomings of topical ophthalmic atropine. The second part of this article focuses on in vitro and animal-based drug studies, which encompass a range of drug targets including the retina, retinal pigment epithelium and sclera. While the latter studies have contributed to a better understanding of how eye growth is regulated, no new antimyopia drug treatments have reached the clinical setting. Less conservative approaches in research, and in particular, the exploration of new bioengineering approaches for drug delivery, are needed to advance this field.

Birth order and myopia

PURPOSE

An association between birth order and reduced unaided vision (a surrogate for myopia) has been observed previously. We examined the association between birth order and myopia directly in four subject groups.

METHODS

Subject groups were participants in (1) the Avon Longitudinal Study of Parents and Children (ALSPAC; UK; age 15 years; N = 4401), (2) the Singapore Cohort Study of Risk Factors for Myopia (SCORM; Singapore; age 13 years; N = 1959), (3) the Raine Eye Health Study (REHS; Australia; age 20 years; N = 1344), and (4) Israeli Defense Force Pre-recruitment Candidates (IDFC; Israel; age 16-22 years; N = 888,277). The main outcome was odds ratios (OR) for myopia in first-born versus non-first-born individuals after adjusting for potential risk factors.

RESULTS

The prevalence of myopia was numerically higher in first-born versus non-first-born individuals in all study groups, but the strength of evidence varied widely. Adjusted ORs (95% confidence intervals, CIs) were: ALSPAC, 1.31 (1.05-1.64); SCORM, 1.25 (0.89-1.77); REHS, 1.18 (0.90-1.55); and IDFC, 1.04 (1.03-1.06). In the large IDFC sample, the effect size was greater (a) for the first-born versus fourth- or higher-born comparison than for the first-born versus second/third-born comparison (p < 0.001) and (b) with increasing myopia severity (p < 0.001).

CONCLUSIONS

Across all studies, the increased risk of myopia in first-born individuals was low (OR < 1.3). Indeed, only the studies with >4000 participants provided strong statistical support for the association. The available evidence suggested the relationship was independent of established risk factors such as time outdoors/reading, and thus may arise through a different causal mechanism.

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

PURPOSE

In chicks, ocular growth inhibition is associated with choroidal thickening and growth stimulation with choroidal thinning, suggesting a mechanistic link between the two responses. Because muscarinic antagonists inhibit the development of myopia in animal models by a non-accommodative mechanism, we tested the hypothesis that agonists would stimulate eye growth and thin the choroid. We also hypothesized that the effective growth-inhibiting antagonists would thicken the choroid.

METHODS

Chicks, age 12-16 days, were used. In vivo: Agonists: Single intravitreal injections (20 μL) of oxotremorine (oxo), pilocarpine (pilo), carbachol (carb), or arecaidine (arec) were given to otherwise untreated eyes. A-scan ultrasonography was done prior to injections, and at 3, 24, 48 and 72 h. Antagonists: -10D lenses were worn on one eye for 4 days. Atropine (atro), pirenzepine (pirz), oxyphenonium (oxy) or dicyclomine (dicy) were injected (20 μL) daily into lens-wearing eyes; saline injections were done as controls. Ultrasonography was done on d1 and on d4; on d4 measurements were done before and 3 h after injections. In vitro: Paired eyecups of retinal pigment epithelium (RPE), choroid and sclera were made from 1-week old chicks. All drugs except atropine were tested on one eyecup, its pair in plain medium. Choroidal thickness was measured at various times over 48 h.

RESULTS

Agonists: In vivo, oxotremorine caused an increase in the rate of axial elongation (drug vs saline: 24-72 h: 338 μm vs 250 μm; p < 0.001). All except pilocarpine caused choroidal thinning by 24 h (oxo, carb and arec vs saline: -25, -35 and -46 μm vs 3 μm). In vitro, all agonists thinned choroids by 24 h (oxo: -6 vs 111 μm; pilo: 45 vs 212 μm; carb: -58 vs 65 μm; arec: 47 vs 139 μm; p < 0.05). Antagonists: Atropine, pirenzepine and oxyphenonium inhibited the development of myopia in negative lens-wearing eyes, and also caused choroidal thickening (drug vs saline: 42, 80, 88 vs 10 μm per 3 h). In vitro, pirenzepine thickened choroids by 3 h (77 vs 2 μm, p < 0.01).

CONCLUSIONS

Muscarinic agonists caused choroidal thinning in intact eyes and eyecups, supporting a role for acetylcholine in the choroidal response to hyperopic defocus or form deprivation. Only oxotremorine stimulated eye growth, which is inconsistent with a muscarinic receptor mechanism for antagonist-induced eye growth inhibition. The dissociation between choroidal thinning and ocular growth stimulation for the other agonists in vivo suggest separate pathways for the two.

Insulin-like growth factor 1 is not associated with high myopia in a large Japanese cohort

PURPOSE

To investigate whether genetic variations in the insulin-like growth factor 1 (IGF-1) gene are associated with high myopia in Japanese.

METHODS

A total of 1,339 unrelated Japanese patients with high myopia (axial length ≥26 mm in both eyes) and two independent control groups were evaluated (334 cataract patients without high myopia and 1,194 healthy Japanese individuals). The mean axial length (mm±SD) in the case group was 29.18±1.85 mm, and the mean spherical equivalent (D±SD) of the phakic eyes was -12.69±4.54 D. We genotyped five tagging single nucleotide polymorphisms (SNPs) in IGF-1: rs6214, rs978458, rs5742632, rs12423791, and rs2162679. Chi-square tests for trend, multivariable logistic regression, and haplotype regression analysis were conducted.

RESULTS

We found no significant association between the IGF-1 SNPs and high or extreme myopia (axial length ≥28 mm in both eyes, 837 subjects) in the additive model, even when compared with the cataract and general population controls, with or without adjustments for age and sex. The evaluation using dominant and recessive models also did not reveal any significant associations. The haplotype analysis with a variable-sized sliding-window strategy also showed a lack of association of IGF-1 SNPs with high or extreme myopia.

CONCLUSIONS

The results of the present study using a Japanese subset do not support the proposal that the IGF-1 gene determines susceptibility to high or extreme myopia in Caucasians and Chinese. Further studies are needed to confirm our reports in other populations and to identify the underlying genetic determinants of these ocular pathological conditions.

Temporal integration of visual signals in lens compensation (a review)

Postnatal eye growth is controlled by visual signals. When wearing a positive lens that causes images to be focused in front of the retina (myopic defocus), the eye reduces its rate of ocular elongation and increases choroidal thickness to move the retina forward to meet the focal plane of the eye. When wearing a negative lens that causes images to be focused behind the retina (hyperopic defocus), the opposite happens. This review summarizes how the retina integrates the constantly changing visual signals in a non-linear fashion to guide eye growth in chicks: (1a) When myopic or hyperopic defocus is interrupted by a daily episode of normal vision, normal vision is more effective in reducing myopia caused by hyperopic defocus than in reducing hyperopia caused by myopic defocus; (1b) when the eye experiences alternating myopic and hyperopic defocus, the eye is more sensitive to myopic defocus than to hyperopic defocus and tends to develop hyperopia, even if the duration of hyperopic defocus is much longer than the duration of myopic defocus; (2) when the eye experiences brief, repeated episodes of defocus by wearing either positive or negative lenses, lens compensation depends on the frequency and duration of individual episodes of lens wear, not just the total daily duration of lens wear; and (3) further analysis of the time constants for the hypothesized internal emmetropization signals show that, while it takes approximately the same amount of time for the signals to rise and saturate during lens-wearing episodes, the decline of the signals between episodes depends strongly on the sign of defocus and the ocular component. Although most extensively studied in chicks, the nonlinear temporal integration of visual signals has been found in other animal models. These findings may help explain the complex etiology of myopia in school-aged children and suggest ways to slow down myopia progression.

Effects of intravitreal insulin and insulin signaling cascade inhibitors on emmetropization in the chick

PURPOSE

Intravitreal insulin has been shown to be a powerful stimulator of myopia in chickens, in particular if the retinal image is degraded or defocused. In most tissues, the insulin receptor activates two main signaling pathways: a) the mitogen-activated protein kinase (MAPK) cascade (e.g., mitogen-activated protein kinasem kinase [MEK] and extracellular regulated kinase [ERK]) and b) the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway. In the current study, insulin was injected, and these pathways were separately inhibited to determine which is activated when the retinal image is defocused by spectacle lenses.

METHODS

Chicks were treated with either +7 D, -7 D, or no lenses. They were intravitreally injected with insulin, the MEK inhibitor U0126, the PI3K inhibitor Ly294002, or a combination of insulin and one of the inhibitors. Refractions and ocular dimension were measured at the beginning and after four days of treatment. The retinal proteins of the chicks were measured with western blots after 2 h and four days of treatment. Incubation occurred with anti-Akt1, anti-Erk1/2, anti-phospho-Akt(Thr308), and anti-phospho-Erk1/2((Thr202/Tyr204)) antibodies, and the ratio between the relative intensity of the phospho-form and the total-form was calculated.

RESULTS

Chicks wearing positive lenses and injected with saline and with PI3K inhibitor compensated for the imposed defocus and became hyperopic. Insulin injections and insulin plus PI3K inhibitor injections prevented lens-induced hyperopia, whereas the MEK inhibitor alone and insulin plus MEK inhibitor had no effect. Obviously, the MEK inhibitor suppressed the effect of insulin on eye growth in the plus lens-treated animals. Chicks treated with negative lenses and injected with insulin, or with insulin plus MEK inhibitor, overcompensated for the imposed defocus. This effect of insulin was not detected in eyes injected with PI3K inhibitor plus insulin, suggesting that the PI3K inhibitor suppressed the effects of insulin in minus lens-treated animals. Insulin increased the ratio of phospho-Akt/total-Akt in animals with normal visual exposure but even more so in chicks wearing plus or minus lenses. The increase was blocked by simultaneous PI3K inhibitor injections in control eyes but not in lens-treated eyes. Insulin also increased the ratio of phospho-ERK/total-ERK in animals with normal visual exposure and in animals wearing positive lenses, compared to U0126- and Ly294002-injected eyes. In contrast, no significant activation of the MEK/ERK pathway was observed in the negative lens-treated animals.

CONCLUSIONS

Intravitreal insulin promoted axial eye growth and stimulated both signaling pathways. The PI3K/Akt pathway was activated in control and plus and minus lens-treated eyes, but the MEK/ERK pathway was activated only with positive lenses or no lenses. With negative lenses, insulin did not stimulate the MEK/ERK signaling cascade. Independent of the pathway stimulated after insulin binding, the effect on insulin was always the same: an increase in eye growth.

The combination of IGF1 and FGF2 and the induction of excessive ocular growth and extreme myopia

Different growth factors have been shown to influence the development of form-deprivation myopia and lens-induced ametropias. However, growth factors have relatively little effect on the growth of eyes with unrestricted vision. We investigate whether the combination of insulin-like growth factor 1 (IGF1) and fibroblast growth factor 2 (FGF2) influence ocular growth in eyes with unrestricted vision. Different doses of IGF1 and FGF2 were injected into the vitreous chamber of postnatal chicks. Measurements of ocular dimensions and intraocular pressure (IOP) were made during and at the completion of different treatment paradigms. Histological and immunocytochemical analyses were performed to assess cell death, cellular proliferation and integrity of ocular tissues. Treated eyes had significant increases in equatorial diameter and vitreous chamber depth. With significant variability between individuals, IGF1/FGF2-treatment caused hypertrophy of lens and ciliary epithelia, lens thickness was increased, and anterior chamber depth was decreased. Treated eyes developed myopia, in excess of 15 diopters of refractive error. Shortly after treatment, eyes had increased intraocular pressure (IOP), which was increased in a dose-dependent manner. Seven days after treatment with IGF1 and FGF2 changes to anterior chamber depth, lens thickness and elevated IOP were reduced, whereas increases in the vitreous chamber were persistent. Some damage to ganglion cells was detected in peripheral regions of the retina at 7 days after treatment. We conclude that the extreme myopia in IGF1/FGF2-treated eyes results from increased vitreous chamber depth, decreased anterior chamber depth, and changes in the lens. We propose that factor-induced ocular enlargement and myopia result from changes to the sclera, lens and anterior chamber depth.

Time outdoors and physical activity as predictors of incident myopia in childhood: a prospective cohort study

PURPOSE

Time spent in "sports/outdoor activity" has shown a negative association with incident myopia during childhood. We investigated the association of incident myopia with time spent outdoors and physical activity separately.

METHODS

Participants in the Avon Longitudinal Study of Parents and Children (ALSPAC) were assessed by noncycloplegic autorefraction at ages 7, 10, 11, 12, and 15 years, and classified as myopic (≤-1 diopters) or as emmetropic/hyperopic (≥-0.25 diopters) at each visit (N = 4,837-7,747). Physical activity at age 11 years was measured objectively using an accelerometer, worn for 1 week. Time spent outdoors was assessed via a parental questionnaire administered when children were aged 8-9 years. Variables associated with incident myopia were examined using Cox regression.

RESULTS

In analyses using all available data, both time spent outdoors and physical activity were associated with incident myopia, with time outdoors having the larger effect. The results were similar for analyses restricted to children classified as either nonmyopic or emmetropic/hyperopic at age 11 years. Thus, for children nonmyopic at age 11, the hazard ratio (95% confidence interval, CI) for incident myopia was 0.66 (0.47-0.93) for a high versus low amount of time spent outdoors, and 0.87 (0.76-0.99) per unit standard deviation above average increase in moderate/vigorous physical activity.

CONCLUSION

Time spent outdoors was predictive of incident myopia independently of physical activity level. The greater association observed for time outdoors suggests that the previously reported link between "sports/outdoor activity" and incident myopia is due mainly to its capture of information relating to time outdoors rather than physical activity.

IGF-1 gene polymorphisms in Polish families with high-grade myopia

PURPOSE

Recent work has suggested that insulin-like growth factor 1 (IGF-1) gene polymorphisms are genetically linked with high-grade myopia (HM), which is a complex-trait eye disorder in which numerous candidate loci and genes are thought to play a role. We investigated whether the IGF-1 single nucleotide polymorphisms (SNPs) rs6214, rs10860860, and rs2946834 are associated with HM (≤-6.0 diopters [D]) and any myopia (≤-0.5 D) phenotype in Polish families.

METHODS

Forty-two multiplex HM Polish families, of whom 127 had HM, participated in the study. All of the family members (n=306) underwent a detailed ophthalmic examination, including axial length measurements. The IGF-1 SNPs rs6214, rs10860860, and rs2946834 were evaluated by PCR-RFLP and direct sequencing methods. Both Family-Based Association Test (FBAT) and family-based Pedigree Disequilibrium Test (PDT) were used to examine the potential association of the IGF-1 SNPs rs6214, rs10860860, and rs2946834 with HM or any myopia. To determine the distribution of the HM-associated SNPs rs6214 and rs10860860, 543 unrelated individuals from the general Polish population were also analyzed.

RESULTS

We found no significant association between the IGF-1 SNPs rs6214, rs10860860, and rs2946834 and HM or any myopia phenotype in Polish HM families. In the general Polish population, the minor allele frequencies of the SNPs rs6214 and rs10860860 did not deviate significantly from the distribution reported for European populations (p=0.629). In the FBAT analysis under the dominant model, the haplotype consisted of T allele of rs10860860, with C allele of rs2946834 of IGF-1 was found less frequently transmitted to HM individuals (p=0.0065), pointing to a nonassociated or protective haplotype.

CONCLUSIONS

Our results do not support recent studies reporting an association of the SNPs rs6214, rs10860860, and rs2946834 in the IGF-1 gene with HM and any myopia phenotypes. Further replication studies involving other populations are needed to investigate the possible role of IGF-1 as a potential myopia candidate gene.

Image defocus and altered retinal gene expression in chick: clues to the pathogenesis of ametropia

PURPOSE

Because of the retina's role in refractive development, this study was conducted to analyze the retinal transcriptome in chicks wearing a spectacle lens, a well-established means of inducing refractive errors, to identify gene expression alterations and to develop novel mechanistic hypotheses about refractive development.

METHODS

One-week-old white Leghorn chicks wore a unilateral spectacle lens of +15 or -15 D for 6 hours or 3 days. With total RNA from the retina/(retinal pigment epithelium, RPE), chicken gene microarrays were used to compare gene expression levels between lens-wearing and contralateral control eyes (n = 6 chicks for each condition). Normalized microarray signal intensities were evaluated by analysis of variance, using a false discovery rate of <10% as the statistical criterion. Selected differentially expressed genes were validated by qPCR.

RESULTS

Very few retina/RPE transcripts were differentially expressed after plus lens wear. In contrast, approximately 1300 transcripts were differentially expressed under each of the minus lens conditions, with minimal overlap. For each condition, low fold-changes typified the altered transcriptome. Differentially regulated genes under the minus lens conditions included many potentially informative signaling molecules and genes whose protein products have roles in intrinsic retinal circadian rhythms.

CONCLUSIONS

Plus or minus lens wear induce markedly different, not opposite, alterations in retina/RPE gene expression. The initial retinal responses to defocus are quite different from those when the eye growth patterns are well established, suggesting that different mechanisms govern the initiation and persistence or progression of refractive errors. The gene lists identify promising signaling candidates and regulatory pathways for future study, including a potential role for circadian rhythms in refractive development.

Insulin, insulin-like growth factor-1, insulin receptor, and insulin-like growth factor-1 receptor expression in the chick eye and their regulation with imposed myopic or hyperopic defocus

PURPOSE

Insulin stimulates eye growth in chicks and this effect is greatly enhanced if the retinal image is degraded by the defocus of either sign. However, it is unclear whether the insulin receptor (IR) is expressed at all in the chicken retina in animals 1-2 weeks post-hatching. We have investigated IR expression and whether IR transcript abundance varies in the fundal layers. To elucidate the possible role of insulin and insulin-like growth factor (IGF)-1 signaling in eye growth regulation, mRNA (mRNA) levels were measured for insulin, IGF-1, IR, and IGF-1 receptor (IGF-1R) during imposed negative or positive defocus.

METHODS

Chicks were treated binocularly with positive or negative spectacle lenses for 4 or 24 h, or they remained untreated (n=6, for each treatment group). Northern blot analyses were performed to screen for transcription variants in the different fundal layers of untreated animals. Real-time PCR was used to quantify IR, IGF-1R, IGF-1, and insulin mRNA levels in the different fundal layers of the chick eye in the three treatment groups.

RESULTS

IR mRNA was found in all the studied tissues, although there is evidence of tissue-specific transcript variations. Three major transcripts were detected for IR. The brain, retina, and choroid showed the longest transcript (4.3 kb), which was not present in the liver. Nevertheless, the liver and brain showed a second transcript (2.6 kb) not present in the retina and choroid. A short transcript (1.3 kb) was the predominant form in the liver and choroid, and it seems to be present in the retinal pigment epithelium (RPE) and sclera as well. In the retina, no significant gene expression changes were found when defocus was imposed. Interestingly, in the RPE, both IR and IGF-1R were already downregulated after short periods (4 h) of positive lens wear. In contrast, IR and IGF-1R were upregulated in the choroid and fibrous sclera during treatment with negative, but not positive, lenses.

CONCLUSIONS

Differences observed in the IR transcript length in different tissues suggest possibly different functions. The differential regulation of IR and IGF-1R in the RPE, choroid, and fibrous sclera is consistent with their involvement in a signaling cascade for emmetropization.

Association of matrix metalloproteinase gene polymorphisms with refractive error in Amish and Ashkenazi families

PURPOSE

Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) are involved in scleral extracellular matrix remodeling and have shown differential expression in experimental myopia. The genetic association of refractive error and polymorphisms in MMP and TIMP genes in Old Order Amish (AMISH) and Ashkenazi Jewish (ASHK) families was investigated.

METHODS

Individuals from 55 AMISH and 63 ASHK families participated in the study. Ascertainment was designed to enrich the families for myopia; the mean spherical equivalent (MSE) refractive error (SD) was -1.61 (2.72) D in the AMISH, and -3.56 (3.32) D in the ASHK. One hundred forty-six common haplotype tagging SNPs covering 14 MMP and 4 TIMP genes were genotyped in 358 AMISH and 535 ASHK participants. Association analyses of MSE and the spherical component of refraction (SPH) were performed separately for the AMISH and the ASHK. Bonferroni-corrected significance thresholds and local false discovery rates were used to account for multiple testing.

RESULTS

After they were filtered for quality-control, 127 SNPs were included in the analyses. No polymorphisms showed statistically significant association to refraction in the ASHK (minimum P = 0.0132). In AMISH, two SNPs showed evidence of association with refractive phenotypes: rs1939008 (P = 0.00016 for SPH); and rs9928731 (P = 0.00026 for SPH). These markers were each estimated to explain <5% of the variance of SPH in the AMISH sample.

CONCLUSIONS

Statistically significant genetic associations of ocular refraction to polymorphisms near MMP1 and within MMP2 were identified in the AMISH but not among the ASHK families. The results suggest that the MMP1 and MMP2 genes are involved in refractive variation in the AMISH. Genetic and/or environmental heterogeneity most likely contribute to differences in association results between ethnic groups.

Genetic association of insulin-like growth factor-1 polymorphisms with high-grade myopia in an international family cohort

PURPOSE

Evidence from human myopia genetic mapping studies (MYP3 locus), modulated animal models, and observations of glycemic control in humans suggests that insulin-like growth factor (IGF)-1 plays a role in the control of eye growth. This study was conducted to determine whether IGF-1 polymorphisms are associated with myopia in a large, international dataset of Caucasian high-grade myopia pedigrees.

METHODS

Two hundred sixty-five multiplex families with 1391 subjects participated in the study. IGF-1 genotyping was performed with 13 selected tag single nucleotide polymorphisms (SNPs) using allelic discrimination assays. A family-based pedigree disequilibrium test (PDT) was performed to test for association. Myopia status was defined using sphere (SPH) or spherical equivalent (SE), and analyses assessed the association of (1) high-grade myopia (<or=-5.00 D), and (2) any myopia (<or=-0.50 D) with IGF-1 markers. Results were declared significant at P<or=0.0038 after Bonferroni correction. Q values that take into account multiple testing were also obtained.

RESULTS

In all, three SNPs-rs10860860, rs2946834, and rs6214-were present at P<0.05. SNP rs6214 showed positive association with both the high-grade- and any-myopia groups (P=2x10(-3) and P=2x10(-3), respectively) after correction for multiple testing.

CONCLUSIONS

The study supports a genetic association between IGF-1 and high-grade myopia. These findings are in line with recent evidence in an experimental myopia model showing that IGF-1 promotes ocular growth and axial myopia. IGF-1 may be a myopia candidate gene for further investigation.

Sonic hedgehog expression and its role in form-deprivation myopia in mice

PURPOSE

To investigate whether sonic hedgehog (Shh) plays a role in postnatal eye development and the development of experimentally induced myopia.

METHODS

Expression of Shh, Patched-1 (Ptc-1), and Gli3 was evaluated in the eyes of 13- to 14-day-old C57B/L6 mice with form-deprivation myopia (FDM) (n = 100) and controls (n = 100) using real-time PCR and Western blot analysis. In a second experiment, 336 mice were divided into two groups: the first wore a unilateral translucent diffuser to induce myopia and the second served as a control. Both groups received four intravitreal injections of either Shh-N (Sonic hedgehog amino-terminal peptide) or cyclopamine (a specific inhibitor of the Shh pathway) every other day. Retinoscopic refraction and axial length measurements were performed on the 11th day of form deprivation. Sections of the eyes were observed using a light microscope.

RESULTS

Inducing myopia caused a significant increase in expression of Shh mRNA (7 days: t = 6.09, p = 0.004; 14 days: t = 3.48, p = 0.025) and protein (7 days: t = 4.06, p = 0.015; 14 days: t = 4.25, p = 0.013). Expression of both Gli3 mRNA (t = 7.61, p = 0.002) and protein (t = 2.89, p = 0.045) increased after 7 days of occlusion. Administration of Shh-N stimulated the development of myopia and axial growth in both occluded (refraction: F = 7.49, p = 0.001; axial length: F = 9.89, p < 0.001) and non-occluded eyes (refraction: F = 14.20, p < 0.001; axial length: F = 20.37, p < 0.001). Cyclopamine reduced myopic refractive error and axial elongation in occluded eyes (refraction: F = 27.91, p < 0.001; axial length: F = 15.18, p < 0.001). It also influenced non-occluded eyes, reducing axial growth and shifting the refraction toward hyperopia (refraction: F = 14.81, p < 0.001; axial length: F = 3.99, p = 0.024). No difference in retinal thickness was found between experimental and control eyes.

CONCLUSIONS

The Shh signaling pathway may influence both form-deprivation myopia and the postnatal growth of eyes with normal visual input.