Molecular genetics of human myopia: an update

Ocular biological parameters and prevalence of myopia in vocational high school and general high school in China

Significance

Higher prevalence of myopia is possibly associated with more extended schooling schedules. Therefore, adjustments to high school curricula may aid in reducing the prevalence of myopia among adolescents.

Purpose

To investigate the prevalence of myopia among 15- to 18-year-old adolescents in Tianjin, China, and to evaluate the impact of different educational schedules on the prevalence of myopia among high school students.

Methods

This is a school-based epidemiological study with a cross-sectional design. Ocular biological parameters and noncycloplegic photorefraction were examined using optical biometry devices and photoscreener devices. Each student’s spherical equivalent (SE) and ocular biometry were recorded, and the prevalence of myopia was calculated.

Results

A total of 2,867 participants (1,519 males and 1,348 females) were tested for non-cycloplegic refraction, axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD) and lens thickness (LT). In this research, the overall prevalence of myopia was 81.6%, with high myopia accounting for 11.8%. Myopia prevalence was substantially higher in general high schools than in vocational high schools, with 86.1 and 70.1%, respectively. There were no significant differences in the prevalence of myopia (p = 0.744) or high myopia (p = 0.851) across the three vocational school years. In the general high school, however, there was an increase of 4.6% (p < 0.05) in myopia prevalence between year 10 and year12.

Conclusion

Comparing vocational and standard high school students, there are considerable disparities in prevalence of myopia, spherical equivalent, and ocular biological parameters. The prevalence of myopia and high myopia increased among standard high school students, but remained relatively consistent among students in vocational schools.

Shedding light on myopia by studying complete congenital stationary night blindness

Myopia is the most common eye disorder, caused by heterogeneous genetic and environmental factors. Rare progressive and stationary inherited retinal disorders are often associated with high myopia. Genes implicated in myopia encode proteins involved in a variety of biological processes including eye morphogenesis, extracellular matrix organization, visual perception, circadian rhythms, and retinal signaling. Differentially expressed genes (DEGs) identified in animal models mimicking myopia are helpful in suggesting candidate genes implicated in human myopia. Complete congenital stationary night blindness (cCSNB) in humans and animal models represents an ON-bipolar cell signal transmission defect and is also associated with high myopia. Thus, it represents also an interesting model to identify myopia-related genes, as well as disease mechanisms. While the origin of night blindness is molecularly well established, further research is needed to elucidate the mechanisms of myopia development in subjects with cCSNB. Using whole transcriptome analysis on three different mouse models of cCSNB (in Gpr179^-/-, Lrit3^-/- and Grm6^-/-), we identified novel actors of the retinal signaling cascade, which are also novel candidate genes for myopia. Meta-analysis of our transcriptomic data with published transcriptomic databases and genome-wide association studies from myopia cases led us to propose new biological/cellular processes/mechanisms potentially at the origin of myopia in cCSNB subjects. The results provide a foundation to guide the development of pharmacological myopia therapies.

Identification and Functional Characterization of a Novel Nonsense Variant in ARR3 in a Southern Chinese Family With High Myopia

ARR3 has been associated with X-linked, female-limited, high myopia. However, using exome sequencing (ES), we identified the first high myopia case with hemizygous ARR3-related mutation in a male patient in a Southern Chinese family. This novel truncated mutation (ARR3: c.569C>G, p.S190*) co-segregated with the disease phenotype in affected family members and demonstrated that high myopia caused by ARR3 is not X-linked, female-limited, where a complicated X-linked inheritance pattern may exist. Thus, our case expanded the variant spectrum in ARR3 and provided additional information for genetic counseling, prenatal testing, and diagnosis. Moreover, we characterized the nonsense-mediated decay of the ARR3 mutant mRNA and discussed the possible underlying pathogenic mechanisms.

Ocular elongation and retraction in foveated reptiles

BACKGROUND

Pronounced asymmetric changes in ocular globe size during eye development have been observed in a number of species ranging from humans to lizards. In contrast, largely symmetric changes in globe size have been described for other species like rodents. We propose that asymmetric changes in the three-dimensional structure of the developing eye correlate with the types of retinal remodeling needed to produce areas of high photoreceptor density. To test this idea, we systematically examined three-dimensional aspects of globe size as a function of eye development in the bifoveated brown anole, Anolis sagrei.

RESULTS

During embryonic development, the anole eye undergoes dynamic changes in ocular shape. Initially spherical, the eye elongates in the presumptive foveal regions of the retina and then proceeds through a period of retraction that returns the eye to its spherical shape. During this period of retraction, pit formation and photoreceptor cell packing are observed. We found a similar pattern of elongation and retraction associated with the single fovea of the veiled chameleon, Chamaeleo calyptratus.

CONCLUSIONS

These results, together with those reported for other foveated species, support the idea that areas of high photoreceptor packing occur in regions where the ocular globe asymmetrically elongates and retracts during development.

The relationship between serum zinc levels and myopia

CLINICAL SIGNIFICANCE

Nutritional status influences growth and development, including that of the eye. However, little attention has been given to possible dietary influences in myopia. This study demonstrates that serum zinc has no relationship with myopia development.

BACKGROUND

Myopia is inherently associated with eye growth and thereby possibly amenable to nutritional influence. A number of Asian studies have reported lower levels of serum zinc in myopic children. This study was designed to assess the relationship between serum zinc and myopia in the Korean population - using a subsample of participants from nationally representative data.

METHODS

Data from the fifth Korea National Health and Nutrition Examination Survey (KNHANES) 2010 were used to explore zinc status in relation to refraction. A total of 304 participants were analysed, ranging in age from 12 to 19-years. Serum zinc levels were measured using inductively coupled plasma mass spectrometry, while refractive error was determined by non-cycloplegic autorefraction. Multivariate analysis was used to examine the association.

RESULTS

A significant majority of participants (n = 255; 84 per cent) were myopic. There was no significant difference in serum zinc levels between myopic and non-myopic children (p = 0.81). In multivariate logistic regression, serum zinc was not significantly associated with myopia after adjustment for age, gender, residence, body mass index, family income and recreational activity. Similarly, no relationship was observed between spherical equivalent refraction and serum zinc within the myopic group (p = 0.46).

CONCLUSION

In a subset of 12-19-year-old participants from the population-representative KNHANES study, no association was found between serum zinc and myopia. However, the lack of a sensitive biomarker for zinc status remains a major limitation in this, and all current studies.

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.

A Bibliometric and Citation Network Analysis of Myopia Genetics

BACKGROUND

To aim of the study was describe the growth of publications on genetic myopia and understand the current research landscape through the analysis of citation networks, as well as determining the different research areas and the most cited publications.

METHODS

The Web of Science database was used to perform the publication search, looking for the terms "genetic*" AND "myopia" within the period between 2009 and October 2020. The CitNetExplorer and CiteSpace software were then used to conduct the publication analysis. To obtain the graphics, the VOSviewer software was used.

RESULTS

A total of 721 publications were found with 2999 citations generated within the network. The year 2019 was singled out as a "key year", taking into account the number of publications that emerged in that year and given that in 2019, 200 loci associated with refractive errors and myopia were found, which is considered to be great progress. The most widely cited publication was "Genome-wide meta-analyses of multiancestry cohorts identify multiple new susceptibility loci for refractive error and myopia", an article by Verhoeven et al., which was published in 2013. By using the clustering function, we were able to establish three groups that encompassed the different research areas within this field: heritability rate of myopia and its possible association with environmental factors, retinal syndromes associated with myopia and the genetic factors that control and influence axial growth of the eye.

CONCLUSIONS

The citation network offers a comprehensive and objective analysis of the main papers that address genetic myopia.

MYP2 locus genes: Sequence variations, genetic association studies and haplotypic association in patients with High Myopia

High Myopia (HM) is a common complex-trait eye disorder. There is essential evidence that genetic factors play a significant role in the development of nonsyndromic high myopia. Identification of susceptibility genes of high myopia will shed light on the pathophysiological mechanism underlying their genesis. This was a case control study examining the prospect of association of DLGAP1, EMILIN2 & MYOM1 genes on MYP2 locus in purely ethnic (Kashmiri) population representing a homogeneous cohort. Genomic DNA was extracted using phenol chloroform and salting out method. Extracted DNA was genotyped for polymorphic variations in MYOM1, EMILIN2 and DLGAP1 genes involving Sanger di-deoxy method. Allele frequencies were tested for Hardy-Weinberg disequilibrium in 224 cases and compared with 220 emmetropic controls. In DLGAP1, documented single nucleotide polymorphism (SNP); Pro517Pro was observed. A previously reported Asn451Asn SNP was observed in EMILIN2. MYOM1 showed five polymorphic variations; two in coding region (Gly333Gly & Gly341Ala) and three intronic (c.1022+23, G>A; c.3418+44 G>T & c.3418+65; C>G). All of the elucidated SNPs were having statistical significant role in increasing or decreasing the risk of disease. Although not statistically significant, a novel Glu507Lys SNP was observed in DLGAP1 (P>0.05). In silico predictions showed MYOM1 Gly341Ala to be benign & tolerated substitution while as DLGAP1 Glu507Lys to be possibly damaging substitution. The studied SNPs followed Over-Dominant, Recessive and Co-Dominant mode of inheritance with specific haplotypes associated with the disease. Our study reveals the involvement of MYP2 locus candidate gene polymorphism in the pathogenesis of HM.

Myopia progression varies with age and severity of myopia

Objective

To investigate annual myopia progression in individuals from South Indian states across different age groups, and its association with age of onset and severity of myopia.

Methods

This retrospective study included the data of 6984 myopes (range: 1–30 years), who visited at least twice to LV Prasad Eye Institute and on whom a standard retinoscopy technique was performed to determine refractive error. Based on spherical equivalent (SE) refractive error, individuals were classified into mild, moderate, high and severe myopic groups. Myopia progression was calculated as difference between SE at 1-year follow-up visit and at baseline. To determine the age-specific myopia progression, individuals were further categorized as myopes who are at least 15 years or younger and those who are above 15.

Results

The mean annual progression of myopia was influenced by both the age group (p < 0.001) and severity type of myopia (p < 0.001). The overall mean myopia progression ranged from -0.07 ± 0.02 D (standard error) to -0.51 ± 0.02 D across different age groups with maximum change in refractive error noted in children aged 6–10 years and the least in adults aged 26–30 years. Myopia progression was greater in severe myopes, followed by high, moderate, mild myopes and in individuals aged ≤ 15 years compared to those aged >15 years (-0.45 ± 0.01 vs. 0.14 ± 0.01, p < 0.001). Severe myopes alone had similar annual myopia progression rate irrespective of age (i.e ≤15 and >15 years, p = 0.71). Early onset of myopia was associated with high myopia in adulthood.

Conclusion

The magnitude of myopia progression in children from South Indian states is comparable to that of Caucasians and Chinese. The greater progression in ‘severe myopes’ across different age groups emphasize the need for regular follow-ups, monitoring axial lengths, and anti-myopia strategies to control myopia progression irrespective of the age and degree of myopia.

Imbalance Between Oxidative Stress and Growth Factors in Human High Myopia

Myopia is one of the commonest eye pathologies that could affect 2.56 billion people by 2020. Today high myopia is a leading cause of blindness worldwide due to associated ocular illness. Nevertheless, the cellular bases for these diseases to develop are unclear in many areas. We conducted a prospective study of oxidative stress and growth factors in human myopic and non myopic eyes in an attempt to increase our understanding of the underlying physiopathological conditions to adequately early diagnose, prevent and treat the retina problem that derives from myopia. Aqueous humor samples were obtained from 41 patients being operated for cataracts in our hospital. Axial length, refractive status and complete ophthalmologic examination were recorded. The VEGF and HGF levels were determined by an ELISA kit. Total antioxidant capacity and total nitrites/nitrate levels were established with a lab kit. We show for the first time an increase in the total nitrite levels in high myopia. We also propose for the first time the concurrence of three factors: myopia, oxidative stress, and oxidative stress together with growth factors in the same group of patients. In this way, it would not be accurate to envision high myopia as a type of normal myopia, but one with more diopters or longer axial length.

Differential Regional Stiffening of Sclera by Collagen Cross-linking

Purpose: Corneal collagen cross-linking by ultraviolet light activation of riboflavin has been used clinically to enhance corneal stiffness. We sought to determine if cross-linking differentially affects scleral regions.Methods: Adjacent, parallel strips of sclera were cut from superolateral, superomedial, inferolateral, and inferomedial quadrants of posterior and equatorial sclera of 12 human cadaver eyes. One of each pair served as control while the other was cross-linked by immersion in 0.1% riboflavin and 365 nm exposure at 6 mW/cm² irradiance for 30 min. Behavior of strips was characterized using a microtensile load cell. Preloaded strips were imaged using orthogonally mounted cameras and optical coherence tomography to determine specimen dimensions including cross-sectional area. Tension was measured during 0.1 mm/s constant rate elongation.Results: Young's modulus (YM), the slope of the relationship relating tensile stress to strain, was calculated at 8% strain, and increased significantly after cross-linking (P < .001). In posterior sclera, mean (± standard error of mean, SEM) YM is increased in the superolateral, superomedial, inferolateral, and inferomedial quadrants by 46 ± 15%, 32 ± 11%, 67 ± 20%, and 53 ± 11%, respectively. In equatorial sclera, YM is increased by 139 ± 43%, 68 ± 27%, 143 ± 92%, and 68 ± 14%, respectively. The YM of pooled equatorial quadrants increased significantly more than that of the pooled posterior quadrants.Conclusions: Scleral collagen cross-linking by ultraviolet activation of riboflavin differentially increases scleral YM more in the equatorial than posterior sclera, and most in the lateral, equatorial sclera. Cross-linking might be used to arrest progressive myopia or to prevent staphyloma formation.

Refractive status and prevalence of myopia among Chinese primary school students

BACKGROUND

The aim of this study was to investigate the prevalence of myopia in key (university-oriented) and non-key elementary schools in China using a traditional and a new criterion for myopia diagnosis in an epidemiological study.

METHODS

This school-based, cross-sectional study examined students from four key schools and seven non-key schools. Non-cycloplegic autorefraction and visual acuity (VA) were performed on each student. Myopia was defined as a spherical equivalent (SE) refractive error not better than -1.00 D. A questionnaire was also administered.

RESULTS

Of the 13,220 students examined, 6,546 (49.5 per cent) had myopia using the criterion of SE not better than -1.00 D. However, 2,246 (34.3 per cent) of these myopes had VA ≥ 0 logMAR in both eyes, indicating they were not functioning as myopes. Thus, a second myopia criterion was adopted: SE refractive error not better than -1.00 D + uncorrected VA ≥ 0 logMAR in at least one eye. By this definition, only 32.5 per cent of the overall sample had myopia. Students in key schools had a higher prevalence of myopia than those in non-key schools (53.8 per cent versus 44.7 per cent) by the initial criterion. By the new criterion, the prevalence of myopia was 41.2 per cent versus 22.7 per cent. Myopia was equal in grade 1 of both school types, but accelerated faster in key schools, where there was a much higher prevalence of myopia by fourth grade, and continued up to 79.2 per cent prevalence by sixth grade based on SE refractive error not better than -1.00 D.

CONCLUSION

Students in more competitive university-oriented elementary schools developed myopia much faster than those in regular schools, although they started with the same level of myopia. Since one-third of the 'myopes' had VA ≥ 0 logMAR in both eyes, they would not be prescribed a correction, or be clinically treated as myopes. A new criterion of SE refractive error not better than -1.00 D + uncorrected VA ≥ 0 logMAR in at least one eye was tested. This criterion is more clinically appropriate and could be used in future epidemiological studies.

A novel G26A variation in 5' half of TGIF1 gene associates with high myopia in ethnic Kashmiri population from India

This study aims to look at novel variations in TGIF1 gene and explores their potential association with high myopia in an ethnic population from Kashmir (India). Genomic DNA was genotyped for polymorphic variations, and allele frequencies were tested for the Hardy–Weinberg disequilibrium in 240 ethnic Kashmiri cases with high myopia with a spherical equivalent of >−6 diopters (D) and compared with emmetropic controls with spherical equivalent within −0.5D in one or both eyes represented by a sample size of 228. In this study, we found a novel sequence variation G26A (GAT to AAT) in 5′ half of TGIF1 gene (p. aspartic acid >asparagine) at a frequency of 62% (148/240, P ≤ 0.0001). Variation appears to associate with high myopia significantly (P ≤ 0.001) as it happens to be present only in high myopia affected individuals. Further, it shows statistical significance for its association with gender and the degree of myopia (P ≤ 0.05). In addition, in silico predictions show that variation likely has an impact on the structure and functional properties of the protein. The assessment of the I-TASSER protein structure showed higher energy for a wild-type protein (−5820.186 kJ/mol) as compared to mutant protein (−6595.593 kJ/mol).

Analysis of genetic networks regulating refractive eye development in collaborative cross progenitor strain mice reveals new genes and pathways underlying human myopia

BACKGROUND

Population studies suggest that genetic factors play an important role in refractive error development; however, the precise role of genetic background and the composition of the signaling pathways underlying refractive eye development remain poorly understood.

METHODS

Here, we analyzed normal refractive development and susceptibility to form-deprivation myopia in the eight progenitor mouse strains of the Collaborative Cross (CC). We used RNA-seq to analyze gene expression in the retinae of these mice and reconstruct genetic networks and signaling pathways underlying refractive eye development. We also utilized genome-wide gene-based association analysis to identify mouse genes and pathways associated with myopia in humans.

RESULTS

Genetic background strongly influenced both baseline refractive development and susceptibility to environmentally-induced myopia. Baseline refractive errors ranged from - 21.2 diopters (D) in 129S1/svlmj mice to + 22.0 D in CAST/EiJ mice and represented a continuous distribution typical of a quantitative genetic trait. The extent of induced form-deprivation myopia ranged from - 5.6 D in NZO/HILtJ mice to - 20.0 D in CAST/EiJ mice and also followed a continuous distribution. Whole-genome (RNA-seq) gene expression profiling in retinae from CC progenitor strains identified genes whose expression level correlated with either baseline refractive error or susceptibility to myopia. Expression levels of 2,302 genes correlated with the baseline refractive state of the eye, whereas 1,917 genes correlated with susceptibility to induced myopia. Genome-wide gene-based association analysis in the CREAM and UK Biobank human cohorts revealed that 985 of the above genes were associated with myopia in humans, including 847 genes which were implicated in the development of human myopia for the first time. Although the gene sets controlling baseline refractive development and those regulating susceptibility to myopia overlapped, these two processes appeared to be controlled by largely distinct sets of genes.

CONCLUSIONS

Comparison with data for other animal models of myopia revealed that the genes identified in this study comprise a well-defined set of retinal signaling pathways, which are highly conserved across different vertebrate species. These results identify major signaling pathways involved in refractive eye development and provide attractive targets for the development of anti-myopia drugs.

Prevalence and Associations of Posterior Segment Manifestations in a Cohort of Egyptian Patients with Pathological Myopia

Purpose: To determine the prevalence of posterior segment manifestations among consecutive patients with pathological myopia attending our University Hospital general ophthalmology clinic and their association with age, refractive error, axial length and each other. Methods: Patients diagnosed with pathological myopia underwent full ophthalmological examination, optical coherence tomography, fluorescein angiography, and ocular ultrasonography. Manifestations detected were recorded for each eye and their prevalence and association with age, refractive error, axial length and each other was determined. Results: A total of 127 eyes of 77 patients with pathological myopia were examined. The most prevalent manifestation was peripheral retinal lesions, found in 63.8% of examined eyes, followed by tigroid fundus, found in 59.1%. Peripheral lesions were significantly associated with more myopia (P = .02) and longer axial length (P = .046). The commonest peripheral lesion was white without pressure, found in 37.8% of eyes. Lattice degeneration was found in 11.8% and snail track degeneration in 4.7% and was not associated with degree of myopia or axial length. Diffuse chorioretinal atrophy was present in 40.9% of eyes, while patchy atrophy was present in 18.9%. Macular holes were present in 4.7% of eyes and were significantly associated with foveoschisis (P = .035) and retinal detachment (P = .003), while foveoschisis was present in 5.5% and was significantly associated with older age (P = .012), longer axial length (P = .010) and patchy chorioretinal atrophy (P = .024). Retinal detachment was found in 6.3% of eyes and retinal breaks in 4.7%. Posterior staphyloma was detected in 33.1% and lacquer cracks and choroidal neovascular membranes in 6.3% of eyes. Conclusions: The prevalence of pathological myopia manifestations may differ between different populations. This may be due to the multiple genetic and environmental factors involved which may result in a variable natural history of the condition among different populations.

Epigenetically dysregulated genes and pathways implicated in the pathogenesis of non-syndromic high myopia

Myopia, commonly referred to as nearsightedness, is one of the most common causes of visual disability throughout the world. It affects more people worldwide than any other chronic visual impairment condition. Although the prevalence varies among various ethnic groups, the incidence of myopia is increasing in all populations across globe. Thus, it is considered a pressing public health problem. Both genetics and environment play a role in development of myopia. To elucidate the epigenetic mechanism(s) underlying the pathophysiology of high-myopia, we conducted methylation profiling in 18 cases and 18 matched controls (aged 4–12 years), using Illumina MethylationEPIC BeadChips array. The degree of myopia was variable among subjects, ranging from −6 to −15D. We identified 1541 hypermethylated CpGs, representing 1745 genes (2.0-fold or higher) (false discovery rate (FDR) p ≤ 0.05), multiple CpGs were p < 5 × 10⁻⁸ with a receiver operating characteristic area under the curve (ROC-AUC) ≥ 0.75 in high-myopia subjects compared to controls. Among these, 48 CpGs had excellent correlation (AUC ≥ 0.90). Herein, we present the first genome-wide DNA methylation analysis in a unique high-myopia cohort, showing extensive and discrete methylation changes relative to controls. The genes we identified hold significant potential as targets for novel therapeutic intervention either alone, or in combination.

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.

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

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

Autosomal-dominant myopia associated to a novel P4HA2 missense variant and defective collagen hydroxylation

We recently described a complex multisystem syndrome in which mild-moderate myopia segregated as an independent trait. A plethora of genes has been related to sporadic and familial myopia. More recently, in Chinese patients severe myopia (MYP25, OMIM:617238) has been linked to mutations in P4HA2 gene. Seven family members complaining of reduced distance vision especially at dusk underwent complete ophthalmological examination. Whole-exome sequencing was performed to identify the gene responsible for myopia in the pedigree. Moderate myopia was diagnosed in the family which was associated to the novel missense variant c.1147A > G p.(Lys383Glu) in the prolyl 4-hydroxylase,alpha-polypeptide 2 (P4HA2) gene, which catalyzes the formation of 4-hydroxyproline residues in the collagen strands. In vitro studies demonstrated P4HA2 mRNA and protein reduced expression level as well as decreased collagen hydroxylation and deposition in mutated fibroblast primary cultures compared to healthy cell lines. This study suggests that P4HA2 mutations may lead to myopic axial elongation of eyeball as a consequence of quantitative and structural alterations of collagen. This is the first confirmatory study which associates a novel dominant missense variant in P4HA2 with myopia in Caucasian patients. Further studies in larger cohorts are advisable to fully clarify genotype-phenotype correlations.

Genes and genetics in eye diseases: a genomic medicine approach for investigating hereditary and inflammatory ocular disorders

Past 25y have witnessed an exponential increase in knowledge and understanding of ocular diseases and their respective genetic underpinnings. As a result, scientists have mapped many genes and their variants that can influence vision and health of our eyes. Based on these findings, it is becoming clear that an early diagnosis employing genetic testing can help evaluate patients' conditions for instituting treatment plan(s) and follow-up care to avoid vision complications later. For example, knowing family history becomes crucial for inherited eye diseases as it can benefit members in family who may have similar eye diseases or predispositions. Therefore, gathering information from an elaborate examination along with complete assessment of past medical illness by ophthalmologists followed by consultation with geneticists can help create a roadmap for making diagnosis and treatment precise and beneficial. In this review, we present an update on ocular genomic medicine that we believe has tremendous potential towards unraveling genetic implications in ocular diseases and patients' susceptibilities. We also discuss translational aspects of genetic ophthalmology and genome engineering that may help advance molecular diagnostics and therapeutics.

Genetic testing for Mendelian myopia

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of genetic testing for Mendelian myopia (MM), a large and heterogeneous group of inherited refraction disorders. Variations in the SLC39A5, SCO2 and COL2A1 genes have an autosomal dominant transmission, whereas those in the LRPAP1, P3H2, LRP2 and SLITRK6 genes have autosomal recessive transmission. The prevalence of MM is currently unknown. Clinical diagnosis is based on clinical findings, family history, ophthalmological examination and other tests depending on complications. The genetic test is useful for confirming diagnosis, and for differential diagnosis, couple risk assessment and access to clinical trials.

Effect of Accommodation on Peripheral Eye Lengths of Emmetropes and Myopes

PURPOSE

To investigate the effect of accommodation on central and peripheral axial lengths in young adult emmetropes and myopes.

METHODS

On-axis and peripheral axial lengths were measured with the Haag-Streit Lenstar in 83 young adult participants for 0D and 6D accommodation demands. A Badal system was used to both correct refractive errors and induce accommodation. Participants were emmetropes (n = 29, mean spherical equivalent refraction +0.35 ± 0.35D), low myopes (32, -1.38 ± 0.73D), and higher myopes (22, -4.30 ± 0.73D). Ages were similar for all groups (22 ± 2 years). Pupils were dilated with 2.5% phenylephrine to allow a large field of measurement while maintaining active accommodation. Axial lengths were measured in 5° steps to ±30° across the horizontal visual field.

RESULTS

With accommodation, axial length increased for all refractive groups at all positions, but with lessening effect away from fixation. Axial length changes were greater for higher myopes than for emmetropes on-axis (higher myopes 41 ± 14 μm, emmetropes 30 ± 12 μm, P = .005), for higher myopes than for low myopes at 30° nasal (P = .03), and for the higher myopes than for the other groups at 20° nasal (P < .05). There were significant correlations between myopia and changes in axial length at all positions, with the highest correlation on-axis (R = 0.30, P < .001).

CONCLUSIONS

During accommodation, eye length increased out to at least ±30° visual angle in young adult myopes and emmetropes. The increase was significantly greater for higher myopes than for the other groups at some positions. At all positions, there were significant correlations between myopia and accommodation-induced changes in axial length.

Bio-environmental factors associated with myopia: An updated review

Experimental studies in animals, as well as observational and intervention studies in humans, seem to support the premise that the development of juvenile myopia is promoted by a combination of the effect of genetic and environmental factors, with a complex interaction between them. The very rapid increase in myopia rates in some parts of the world, such as Southeast Asia, supports a significant environmental effect. Several lines of evidence suggest that humans might respond to various external factors, such as increased activity in near vision, increased educational pressure, decreased exposure to sunlight outdoors, dietary changes (including increased intake of carbohydrates), as well as low light levels indoors. All these factors could be associated with a higher prevalence of myopia.

X-linked heterozygous mutations in ARR3 cause female-limited early onset high myopia

PURPOSE

To identify genetic mutations in three families with early onset high myopia (eoHM) limited to female members.

METHODS

Genomic DNA was collected from participating members of families XF1, XF2, and XF3. Genome-wide linkage scans were performed on the largest family (XF1). Whole exome sequencing was performed on seven samples, including five samples (four affected and one unaffected) from family XF1, as well as the two probands from family XF2 and XF3. Variants were analyzed with multistep bioinformatics analyses. Sanger-dideoxy sequencing was used to verify candidate variations in families and controls.

RESULTS

The genome-wide linkage scans performed on family XF1 detected a candidate locus on chromosome Xp11.1-Xq13.3 with a maximum logarithm of the odds (LOD) score of 2.48 and 3.01 for markers DXS991 and DXS986, respectively. Parallel whole exome sequencing identified a novel c.893C>A (p.Ala298Asp) mutation in ARR3 located on Xq13.1 in family XF1, which was shared by all four affected individuals but not the unaffected individual. Two other novel mutations in ARR3, c.298C>T (p.Arg100*) and c.239T>C (p.Leu80Pro), were detected in families XF2 and XF3, respectively. These mutations were predicted to be damaging and were not present in the normal controls and existing databases. All three mutations cosegregated with eoHM in each of the three families, in which all heterozygous female members are affected whereas all hemizygous male family members are not affected. Transmission of the mutations and eoHM in the three families demonstrates an unusual pattern of X-linked female-limited inheritance.

CONCLUSIONS

These data suggest that heterozygous mutations in ARR3 might be responsible for X-linked female-limited eoHM in the three families, a pattern contrary to the standard X-linked recessive trait. To our knowledge, eoHM is the first human disease associated with mutations in ARR3 and the second X-linked female-limited disease identified thus far. Identification of ARR3 associated with X-linked female-limited trait provides not only additional evidence of this unusual hereditary pattern but also an additional model for investigating the molecular mechanism responsible for female-limited phenotypes.

Myopia Genetics-The Asia-Pacific Perspective

Myopia is a major cause of visual impairment worldwide. In particular, high myopia is associated with serious blinding complications, including retinal detachment, chorioretinal degeneration, and choroidal neovascularization. Myopia is multifactorial in etiology, resulting from the interaction of environmental and genetic risk factors. During the past 2 decades, a large number of gene loci and variants have been identified for myopia. There are more than 20 myopia-associated loci spanning all chromosomes. Earlier findings were obtained mainly from family linkage analyses and candidate gene studies, and more recent results are principally from genome-wide association studies and exome sequencing. Some genetic associations have been successfully validated and replicated in populations of different geographic localities and ethnicities, but some have not. Compared with Whites, Asian populations-in particular Japanese, Korean, and Chinese-have a much higher prevalence of myopia, especially high myopia. Both genetic and environmental factors contribute to such ethnic variations. This review attempts to summarize and compare the allelic frequencies of gene variants known to be associated with myopia in different ethnic groups, especially in the Asia-Pacific region.

Current Understanding of the Genetic Architecture of Rhegmatogenous Retinal Detachment

Rhegmatogenous retinal detachment (RRD) is a common and potentially blinding surgical retinal disease. While the precise molecular mechanisms leading to RRD are poorly understood, there is an increasing body of literature supporting the role of heritable factors in the pathogenesis of the condition. Much work has been undertaken investigating genes important in syndromic forms of RRD (e.g., Stickler, Wagner Syndrome, etc.) and research pertaining to genetic investigations of idiopathic or non-syndromic RRD has also recently been reported. To date, at least 12 genetic loci have been implicated in the development of syndromes of which RRD is a feature. A recent GWAS identified five loci implicated in the development of idiopathic RRD.This article provides an overview of the genetic mechanisms of both syndromic and idiopathic RRD. The genetics of predisposing conditions, such as myopia and lattice degeneration, are also discussed.

Topical Atropine in the Control of Myopia

Atropine has been used for more than a century to arrest myopia progression. Compelling evidence of its protective effect has been reported in well-designed clinical studies, mainly performed during the last two decades. However, its exact mechanism of action has not been determined. Experimental findings have shown that the mechanism is not related to accommodation, as was thought for decades. A review of the published literature revealed a significant amount of evidence supporting its safety and efficacy at a concentration of 1.0%, and at lower concentrations (as low as 0.01%).

Myopia in schoolchildren in a rural community in the State of Mexico, Mexico

PURPOSE

This study sought to determine the prevalence of myopia in schoolchildren of a rural population in Mexico.

METHODS

A cross-sectional study was conducted in 317 children between 6 and 12 years old. A complete refractive examination was performed, including static retinoscopy without cycloplegic agents. All procedures were conducted according to the Declaration of Helsinki.

RESULTS

In total, 9.7% (95% CI: 13.07-6.52) of the examined children were myopic (spherical equivalent ≤ -0.50 D), 4.4% (95% CI: 6.66-2.14) presented astigmatism (cylinder ≤ -1.50 D), and 5.4% (95% CI: 7.89-2.91) presented hyperopia (spherical equivalent ≥ +0.50 D).

CONCLUSION

Additional research is required to assess the prevalence of refractive errors in rural areas in Mexico, to analyze the associated risk factors, and to implement appropriate eye care plans for this population.

Baseline peripheral refractive error and changes in axial refraction during one year in a young adult population

PURPOSE

To determine whether the initial characteristics of individual patterns of peripheral refraction relate to subsequent changes in refraction over a one-year period.

METHODS

54 myopic and emmetropic subjects (mean age: 24.9±5.1 years; median 24 years) with normal vision were recruited and underwent conventional non-cycloplegic subjective refraction. Peripheral refraction was also measured at 5° intervals over the central 60° of horizontal visual field, together with axial length. After one year, measurements of subjective refraction and axial length were repeated on the 43 subjects who were still available for examination.

RESULTS

In agreement with earlier studies, higher myopes tended to show greater relative peripheral hyperopia. There was, however, considerable inter-subject variation in the pattern of relative peripheral refractive error (RPRE) at any level of axial refraction. Across the group, mean one-year changes in axial refraction and axial length did not differ significantly from zero. There was no correlation between changes in these parameters for individual subjects and any characteristic of their RPRE.

CONCLUSION

No evidence was found to support the hypothesis that the pattern of RPRE is predictive of subsequent refractive change in this age group.

Assessing the Genetic Predisposition of Education on Myopia: A Mendelian Randomization Study

Myopia is the largest cause of uncorrected visual impairments globally and its recent dramatic increase in the population has made it a major public health problem. In observational studies, educational attainment has been consistently reported to be correlated to myopia. Nonetheless, correlation does not imply causation. Observational studies do not tell us if education causes myopia or if instead there are confounding factors underlying the association. In this work, we use a two-step least squares instrumental-variable (IV) approach to estimate the causal effect of education on refractive error, specifically myopia. We used the results from the educational attainment GWAS from the Social Science Genetic Association Consortium to define a polygenic risk score (PGRS) in three cohorts of late middle age and elderly Caucasian individuals (N = 5,649). In a meta-analysis of the three cohorts, using the PGRS as an IV, we estimated that each z-score increase in education (approximately 2 years of education) results in a reduction of 0.92 ± 0.29 diopters (P = 1.04 × 10(-3) ). Our estimate of the effect of education on myopia was higher (P = 0.01) than the observed estimate (0.25 ± 0.03 diopters reduction per education z-score [∼2 years] increase). This suggests that observational studies may actually underestimate the true effect. Our Mendelian Randomization (MR) analysis provides new evidence for a causal role of educational attainment on refractive error.

Efficacy of Blue-Light Cross-linking on Human Scleral Reinforcement

PURPOSE

To evaluate the biomechanical effects of collagen cross-linking by riboflavin/blue light (460 nm) on human sclera.

METHODS

Forty-two sclera samples from donated human eyes were treated with riboflavin at 0.5% on the equatorial sclera for 20 minutes and then randomly divided into seven groups and irradiated, respectively, with blue light at different intensities (14.6, 19.5, 22.5, 26, 32.5, and 40.6 mW/cm) for 20 minutes using a light-emitting diode source with an exposure area of 10 mm in diameter. The untreated samples constituted the control group. During irradiation, continuous riboflavin solution infiltration was carried out for 20 minutes. Stress-strain measurements of scleral strips were performed with a biomaterial tester. Stress data and Young modulus values in different groups were compared by one-way analysis of variance.

RESULTS

Blue-light (460 nm) cross-linking was efficient in stiffening human sclera strips. Interestingly, eyes treated with 22.5 mW/cm exhibited higher Young modulus values (19.12 [±4.88] MPa) at 8% strain compared with other groups, representing a 307.68% increase over control eye values (4.69 [±1.26] MPa). Stress and Young modulus increased gradually with irradiation intensity from 19.5 to 22.5 mW/cm before decreasing for higher intensities.

CONCLUSIONS

The biomechanical strength of human sclera may be enhanced by collagen cross-linking with riboflavin/460 nm blue-light irradiation; the dose of 22.5 mW/cm might be used for blue-light (460 nm) scleral cross-linking to achieve a higher efficacy.

APLP2 Regulates Refractive Error and Myopia Development in Mice and Humans

Myopia is the most common vision disorder and the leading cause of visual impairment worldwide. However, gene variants identified to date explain less than 10% of the variance in refractive error, leaving the majority of heritability unexplained (“missing heritability”). Previously, we reported that expression of APLP2 was strongly associated with myopia in a primate model. Here, we found that low-frequency variants near the 5’-end of APLP2 were associated with refractive error in a prospective UK birth cohort (n = 3,819 children; top SNP rs188663068, p = 5.0 × 10⁻⁴) and a CREAM consortium panel (n = 45,756 adults; top SNP rs7127037, p = 6.6 × 10⁻³). These variants showed evidence of differential effect on childhood longitudinal refractive error trajectories depending on time spent reading (gene x time spent reading x age interaction, p = 4.0 × 10⁻³). Furthermore, Aplp2 knockout mice developed high degrees of hyperopia (+11.5 ± 2.2 D, p < 1.0 × 10⁻⁴) compared to both heterozygous (-0.8 ± 2.0 D, p < 1.0 × 10⁻⁴) and wild-type (+0.3 ± 2.2 D, p < 1.0 × 10⁻⁴) littermates and exhibited a dose-dependent reduction in susceptibility to environmentally induced myopia (F(2, 33) = 191.0, p < 1.0 × 10⁻⁴). This phenotype was associated with reduced contrast sensitivity (F(12, 120) = 3.6, p = 1.5 × 10⁻⁴) and changes in the electrophysiological properties of retinal amacrine cells, which expressed Aplp2. This work identifies APLP2 as one of the “missing” myopia genes, demonstrating the importance of a low-frequency gene variant in the development of human myopia. It also demonstrates an important role for APLP2 in refractive development in mice and humans, suggesting a high level of evolutionary conservation of the signaling pathways underlying refractive eye development.

Gene variants identified by GWAS studies to date explain only a small fraction of myopia cases because myopia represents a complex disorder thought to be controlled by dozens or even hundreds of genes. The majority of genetic variants underlying myopia seems to be of small effect and/or low frequency, which makes them difficult to identify using classical genetic approaches, such as GWAS, alone. Here, we combined gene expression profiling in a monkey model of myopia, human GWAS, and a gene-targeted mouse model of myopia to identify one of the “missing” myopia genes, APLP2. We found that a low-frequency risk allele of APLP2 confers susceptibility to myopia only in children exposed to large amounts of daily reading, thus, providing an experimental example of the long-hypothesized gene-environment interaction between nearwork and genes underlying myopia. Functional analysis of APLP2 using an APLP2 knockout mouse model confirmed functional significance of APLP2 in refractive development and implicated a potential role of synaptic transmission at the level of glycinergic amacrine cells of the retina for the development of myopia. Furthermore, mouse studies revealed that lack of Aplp2 has a dose-dependent suppressive effect on susceptibility to form-deprivation myopia, providing a potential gene-specific target for therapeutic intervention to treat myopia.

Genetic association study between INSULIN pathway related genes and high myopia in a Han Chinese population

To investigate the association between insulin (INS) pathway related genes, including INS, insulin receptor (INSR), insulin receptor substrate 1 (IRS1), insulin-like growth factor 2 (IGF2), IGF2 receptor (IGF2R) and IGF binding protein 1 (IGFBP1), and high myopia (HM) in a Han Chinese population, we have genotyped 24 single nucleotide polymorphisms (SNPs) of these genes in this cohort by Sequenom MassARRAY method. The genotyping data was analyzed by χ(2) test and the linkage disequilibrium block structure was examined by Haploview software. SNPs in the INS-IGF2 region (rs2070762 and rs1003483), and the INSR gene (rs3745551 and rs2229429) showed significant association with HM (allelic P = 0.0085, 0.0494, 0.0171 and 0.0238, respectively). Under the model of risk genotype combination of INSR and IRS1, carrying the variant allele (A) of the IRS1 Gly972Arg SNP (rs1801278) further increased the risk among the rs2229429T allele carriers (odds ratio 6.865, 95 % confidence interval 1.533-30.745). None of the SNPs in the IGF2R and IGFBP1 genes were found to be significantly associated with HM. Genetic variants in the insulin signaling pathway genes may increase the susceptibility of high myopia in Han Chinese.

Myopia and level of education: results from the Gutenberg Health Study

PURPOSE

To analyze the association between myopia and educational level in an adult European cohort.

DESIGN

Population-based cross-sectional study.

PARTICIPANTS

A cohort of the Gutenberg Health Study, including 4658 eligible enrollees between 35 and 74 years of age.

METHODS

We applied a standardized protocol entailing a comprehensive questionnaire; thorough ophthalmic, general, cardiovascular, and psychological examinations; and laboratory tests, including genetic analyses. We documented achievement levels in school education and post-school professional education. The spherical equivalent (SE) was determined by noncycloplegic autorefractometry. We fitted mixed linear models including age, gender, and 45 myopia-associated single nucleotide polymorphisms (SNP) as covariates.

MAIN OUTCOME MEASURES

Prevalence and magnitude of myopia in association with years spent in school and level of post-school professional education.

RESULTS

Individuals who graduated from school after 13 years were more myopic (median, -0.5 diopters [D]; first quartile [Q1]/third quartile [Q3], -2.1/0.3 D) than those who graduated after 10 years (median, -0.2 D; Q1/Q3, -1.3/0.8 D), than those who graduated after 9 years (median, 0.3 D; Q1/Q3, -0.6/1.4 D), and than those who never finished secondary school (median, 0.2 D; Q1/Q3, -0.5/1.8 D; P<0.001, respectively). The same holds true for persons with a university degree (median, -0.6 D; Q1/Q3, -2.3/0.3 D) versus those who finished secondary vocational school (median, 0 D; Q1/Q3, -1.1/0.8 D) or primary vocational school (median, 0 D; Q1/Q3, -0.9/1.1 D) versus persons without any post-school professional qualification (median, 0.6 D; Q1/Q3, -0.4/1.7 D; P<0.001, respectively). Of persons who graduated from school after 13 years, 50.9% were myopic (SE, ≤-0.5 D) versus 41.6%, 27.1%, and 26.9% after 10 years, in those who graduated after 9 years, and in those who never graduated from secondary school, respectively (P<0.001). In university graduates, the proportion of myopic persons was higher (53%) than that of those who graduated from secondary (34.8%) or primary (34.7%) vocational schools and than in those without any professional training (23.9%; P<0.001, respectively). In multivariate analyses: higher school and professional levels of education were associated with a more myopic SE independent of gender. There was a small effect of age and SNPs.

CONCLUSIONS

Higher levels of school and post-school professional education are associated with a more myopic refraction. Participants with higher educational achievements more often were myopic than individuals with less education.

Polymorphism in the 11q24.1 genomic region is associated with myopia: a comprehensive genetic study in Chinese and Japanese populations

PURPOSE

To evaluate the association of polymorphisms in the 11q24.1 genomic region and the CTNND2 gene with myopia.

METHODS

We conducted a comprehensive meta-analysis included 6,954 cases and 9,346 controls. Odds ratios (ORs) were calculated using Carlin's method. Publication bias was assessed using Egger et al.'s approach. Sensitivity, heterogeneity, and trim and fill analyses were also conducted.

RESULTS

For the 11q24.1 genomic region, the rs11218544 polymorphism showed significant association with myopia [OR and 95% confidence interval (CI): 1.167 (1.032-1.319), p=0.013], while rs577948 showed no association with the disease [OR and 95%CI: 0.988 (0.727-1.342), p=0.936]. For the CTNND2 gene, neither rs6885224 nor rs12716080 was significantly associated with myopia {rs6885224: [OR and 95%CI: 1.051 (0.795-1.391), p=0.725], rs12716080: [OR and 95%CI: 1.173 (0.990-1.390), p=0.065]}.

CONCLUSIONS

Our study indicated that the 11q24.1 genomic region, and particularly the rs11218544 polymorphism, has a genetic association with the development of myopia.

Mutations in SCO2 are associated with autosomal-dominant high-grade myopia

Myopia, or near-sightedness, is an ocular refractive error of unfocused image quality in front of the retinal plane. Individuals with high-grade myopia (dioptric power greater than -6.00) are predisposed to ocular morbidities such as glaucoma, retinal detachment, and myopic maculopathy. Nonsyndromic, high-grade myopia is highly heritable, and to date multiple gene loci have been reported. We performed exome sequencing in 4 individuals from an 11-member family of European descent from the United States. Affected individuals had a mean dioptric spherical equivalent of -22.00 sphere. A premature stop codon mutation c.157C>T (p.Gln53*) cosegregating with disease was discovered within SCO2 that maps to chromosome 22q13.33. Subsequent analyses identified three additional mutations in three highly myopic unrelated individuals (c.341G>A, c.418G>A, and c.776C>T). To determine differential gene expression in a developmental mouse model, we induced myopia by applying a -15.00D lens over one eye. Messenger RNA levels of SCO2 were significantly downregulated in myopic mouse retinae. Immunohistochemistry in mouse eyes confirmed SCO2 protein localization in retina, retinal pigment epithelium, and sclera. SCO2 encodes for a copper homeostasis protein influential in mitochondrial cytochrome c oxidase activity. Copper deficiencies have been linked with photoreceptor loss and myopia with increased scleral wall elasticity. Retinal thinning has been reported with an SC02 variant. Human mutation identification with support from an induced myopic animal provides biological insights of myopic development.

Association mapping of the high-grade myopia MYP3 locus reveals novel candidates UHRF1BP1L, PTPRR, and PPFIA2

PURPOSE

Myopia, or nearsightedness, is a common ocular genetic disease for which over 20 candidate genomic loci have been identified. The high-grade myopia locus, MYP3, has been reported on chromosome 12q21-23 by four independent linkage studies.

METHODS

We performed a genetic association study of the MYP3 locus in a family-based high-grade myopia cohort (n = 82) by genotyping 768 single-nucleotide polymorphisms (SNPs) within the linkage region. Qualitative testing for high-grade myopia (sphere ≤ -5 D affected, > -0.5 D unaffected) and quantitative testing on the average dioptric sphere were performed.

RESULTS

Several genetic markers were nominally significantly associated with high-grade myopia in qualitative testing, including rs3803036, a missense mutation in PTPRR (P = 9.1 × 10(-4)) and rs4764971, an intronic SNP in UHRF1BP1L (P = 6.1 × 10(-4)). Quantitative testing determined statistically significant SNPs rs4764971, also found by qualitative testing (P = 3.1 × 10(-6)); rs7134216, in the 3' untranslated region (UTR) of DEPDC4 (P = 5.4 × 10(-7)); and rs17306116, an intronic SNP within PPFIA2 (P < 9 × 10(-4)). Independently conducted whole genome expression array analyses identified protein tyrosine phosphatase genes PTPRR and PPFIA2, which are in the same gene family, as differentially expressed in normal rapidly growing fetal relative to normal adult ocular tissue (confirmed by RT-qPCR).

CONCLUSIONS

In an independent high-grade myopia cohort, an intronic SNP in UHRF1BP1L, rs4764971, was validated for quantitative association, and SNPs within PTPRR (quantitative) and PPFIA2 (qualitative and quantitative) approached significance. Three genes identified by our association study and supported by ocular expression and/or replication, UHRF1BP1L, PTPRR, and PPFIA2, are novel candidates for myopic development within the MYP3 locus that should be further studied.

[Nature or nurture: effects of parental ametropia on children's refractive errors]

PURPOSE

The aim of this study was to quantify the degree of association between juvenile refraction errors and parental refraction status.

METHODS

Using a simple questionnaire we conducted a cross-sectional study to determine the prevalence and magnitudes of refractive errors and of parental refraction status in a sample (n=728) of 10- to 18-year-old Austrian grammar school students.

RESULTS

Students with myopia or hyperopia were more likely to have ametropic parents and refraction was more myopic in juveniles with one or two parents being ametropic. The prevalence of myopia in children with 2 ametropic parents was 54%, decreasing to 35% in pupils with 1 and to 13% in children with no ametropic parents. The odds ratio for 1 and 2 compared with no ametropic parents was 8.3 and 3.7 for myopia and 1.3 and 1.6 for hyperopia, respectively. Furthermore, the data indicate a stronger influence of the maternal ametropia on children's refractive errors than paternal ametropia.

CONCLUSIONS

Genetic factors play a significant role in refractive error and may be of dominant influence for school myopia under conditions of low environmental variation.

A genome-wide meta-analysis identifies two novel loci associated with high myopia in the Han Chinese population

High myopia, highly prevalent in the Chinese population, is a leading cause of visual impairment worldwide. Genetic factors play a critical role in the development of this visual disorder. Genome-wide association studies in recent years have revealed several chromosomal regions that contribute to its progression. To identify additional genetic variants for high myopia susceptibility, we used a genome-wide meta-analysis to examine the associations between the disease and 286 031 single-nucleotide polymorphisms (SNPs) in a combined cohort of 665 cases and 960 controls. The most significant SNPs (n = 61) were genotyped in a replication cohort (850 cases and 1197 controls), and 14 SNPs were further tested through genotyping in two additional validation cohorts (combined 1278 cases and 2486 controls). As a result of this analysis, four SNPs reached genome-wide significance (P < 2.0 × 10(-7)). The most significantly associated SNP, rs2730260 [overall P = 8.95 × 10(-14); odds ratio (95% CI) =1.33 (1.23-1.44)], is located in the VIPR2 gene, which is located in the MYP4 locus. The other three SNPs (rs7839488, rs4395927 and rs4455882) in the same linkage disequilibrium block are located in the SNTB1 gene, with -P values ranging from 1.13 × 10(-8) to 2.13 × 10(-11). The VIPR2 and SNTB1 genes are expressed in the retina and the retinal pigment epithelium and have been previously reported to have potential functions for the pathogenesis of myopia. Our results suggest that variants of the VIPR2 and SNTB1 genes increase susceptibility to high myopia in Han Chinese.

[Clinical risk factors for progressive myopia]

The average worldwide frequency of myopia is approximately 30 % and is traditionally subdivided into school myopia and pathological myopia. A further distinction is made between progressive myopia and stationary myopia. There is a high correlation between the frequency of myopia and urbanization and training. Risk factors for development of myopia are close-up work, lack of outdoor activity, biometrical variables of the eye and genetic risk factors. Development of myopia can be positively influenced by peripheral focusing, increased exposure to light and in the future possibly pharmacologically.

The impact of severity of parental myopia on myopia in Chinese children

PURPOSE

To assess the impact of severity of parental myopia on myopia in Chinese children.

METHODS

Children aged 12 to 15 years were identified from a population-based sample in Guangzhou. Children's myopia was defined as a spherical equivalent refraction of ≤0.5 D based on cycloplegic (1% cyclopentolate) autorefraction. Using a questionnaire reported by the parents, the parental myopia was confirmed and the severity of myopia on the right eyes was classified into mild (<3.0 D myopia), moderate (3.0 to 6.0 D myopia), and high (>6.0 D myopia) myopia.

RESULTS

Information was available for 1567 children aged 12 to 15 years. Analysis was restricted to children with no myopia in one parent and no, mild, moderate, or high myopia in the other. The prevalence of myopia in children was 53.5, 65.1, 76.3, and 80.6% when the severity of myopia in the second parent was no, mild, moderate, and high, and the prevalence of high myopia (spherical equivalent >6.0 D myopia) in children was 1.4, 2.9, 8.5, and 16.1% in the corresponding groups of parental myopia severity. Of the children with high myopia, 45.3% had parents with no reported myopia.

CONCLUSIONS

More severe myopia in one parent results in an increased risk of myopia in the children. However, most highly myopic children did not have a highly myopic parent and also half did not have any reported parental myopia. This suggests that while genetic factors contribute to the development of more severe myopia, environmental factors also contribute to high myopia in children in Guangzhou.

Association of markers at chromosome 15q14 in Chinese patients with moderate to high myopia

PURPOSE

To investigate the association of two reported regions on chromosome 15 with moderate to high myopia in two Chinese cohorts from southern China.

METHODS

Two candidate regions on 15q14 and 15q25 were selected based on reported association with refractive error in the literature. Five single nucleotide polymorphisms (SNPs) were genotyped in 300 university students with high myopia at Guangzhou and 308 without refractive error, and 96 university students of Chaoshan Chinese origin with moderate to high myopia and 96 without refractive error. Genotypes were evaluated using direct sequencing and analyzed with chi-square, Armitage trend, and Mantel-Haenszel tests, and regression analysis.

RESULTS

Of the five SNPs screened, alleles of rs634990 and rs524952 in the 15q14 region showed evidence of allelic association with moderate to high myopia (p<8.81×10(-7) and p<1.57×10(-6), respectively) in the Guangzhou group, but not in the Chaoshan group. The SNPs at 15q25 did not show significant association in any group. Association of rs634990 and rs524952 were still significant when both groups were combined into a single analysis (p<1.66×10(-6) and p<2.72×10(-6), respectively), and for genotypic, additive, and dominant models.

CONCLUSIONS

This study confirms the significant association of rs634990 and rs524952 on chromosome 15q14 previously reported in European and Japanese populations with high myopia in the Guangzhou but not the Chaoshan Chinese populations, suggesting that genetic contributors to high myopia in the Chaoshan population might be different from other Chinese populations.

The visual system of zebrafish and its use to model human ocular diseases

Free swimming zebrafish larvae depend mainly on their sense of vision to evade predation and to catch prey. Hence, there is strong selective pressure on the fast maturation of visual function and indeed the visual system already supports a number of visually driven behaviors in the newly hatched larvae.The ability to exploit the genetic and embryonic accessibility of the zebrafish in combination with a behavioral assessment of visual system function has made the zebrafish a popular model to study vision and its diseases.Here, we review the anatomy, physiology, and development of the zebrafish eye as the basis to relate the contributions of the zebrafish to our understanding of human ocular diseases.

Large scale international replication and meta-analysis study confirms association of the 15q14 locus with myopia. The CREAM consortium

Myopia is a complex genetic disorder and a common cause of visual impairment among working age adults. Genome-wide association studies have identified susceptibility loci on chromosomes 15q14 and 15q25 in Caucasian populations of European ancestry. Here, we present a confirmation and meta-analysis study in which we assessed whether these two loci are also associated with myopia in other populations. The study population comprised 31 cohorts from the Consortium of Refractive Error and Myopia (CREAM) representing 4 different continents with 55,177 individuals; 42,845 Caucasians and 12,332 Asians. We performed a meta-analysis of 14 single nucleotide polymorphisms (SNPs) on 15q14 and 5 SNPs on 15q25 using linear regression analysis with spherical equivalent as a quantitative outcome, adjusted for age and sex. We calculated the odds ratio (OR) of myopia versus hyperopia for carriers of the top-SNP alleles using a fixed effects meta-analysis. At locus 15q14, all SNPs were significantly replicated, with the lowest P value 3.87 × 10(-12) for SNP rs634990 in Caucasians, and 9.65 × 10(-4) for rs8032019 in Asians. The overall meta-analysis provided P value 9.20 × 10(-23) for the top SNP rs634990. The risk of myopia versus hyperopia was OR 1.88 (95 % CI 1.64, 2.16, P < 0.001) for homozygous carriers of the risk allele at the top SNP rs634990, and OR 1.33 (95 % CI 1.19, 1.49, P < 0.001) for heterozygous carriers. SNPs at locus 15q25 did not replicate significantly (P value 5.81 × 10(-2) for top SNP rs939661). We conclude that common variants at chromosome 15q14 influence susceptibility for myopia in Caucasian and Asian populations world-wide.

An association study of the COL1A1 gene and high myopia in a Han Chinese population

PURPOSE

Single nucleotide polymorphisms (SNPs) in the collagen type I (COL1A1) gene have been shown to be significantly associated with high myopia in a Japanese population. This present study was conducted to investigate whether COL1A1 is associated with high myopia in a Han Chinese population.

METHODS

High myopia is defined by a spherical equivalent of less than or equal to -6.00 diopter sphere and an axial length longer than or equal to 26.0 mm in the affected eye. We genotyped rs2075555 and rs2269336 SNPs in COL1A1 in a Ha n Chinese group composed of 697 high myopia patients and 762 normal controls.

RESULTS

Neither of the two SNPs showed significant association with high myopia (p(allelic)=0.252 for rs2075555, and p(allelic)=0.699 for rs2269336).

CONCLUSIONS

Our study revealed that SNPs in COL1A1 are not significantly associated with high myopia in the Han Chinese population.