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Introduction: Hepatocyte growth factor (HGF) and hepatocyte growth factor receptor (C-MET) genes have previously been reported to be associated with myopia in Asian family-based and case-control association studies, respectively. We examined whether these genes were associated with myopia in a Caucasian family dataset biased towards high myopia., Methods: Participating families had at least one offspring with high myopia (< or = -5.00 diopters [D]). Genotyping was performed with tagging single nucleotide polymorphisms (SNPs) for each candidate gene using Taqman allelic discrimination assays. The data were analyzed with two family-based association methods, the pedigree disequilibrium test (PDT) and the association in the presence of linkage (APL) test. Analyses compared 1) high myopia (<-5.00 D), 2) mild to moderate myopia (-0.50 to -5.00 D), 3) any myopia (<-0.50 D) and 4) extreme high myopia (< or =-10.00 D) versus emmetropia using refractive error as either sphere (SPH) or spherical equivalent (SE=sphere + [cylinder/2]). Bonferroni correction was applied to adjust for multiple testing leading to significance levels of 0.0125 for HGF and 0.008 for C-MET. Two and three-marker sliding window haplotype association tests using APL were also performed for HGF markers. Significance levels for haplotype association testing were set at 0.01 for the global tests, and 0.007 for the three marker haplotype specific tests and 0.0125 for the two marker haplotype specific tests., Results: A total of 146 multiplex families consisting of 649 Caucasian subjects were included. The HGF SNP, rs3735520 (APL p=0.002768 for SPH and 0.005609 for SE), and the haplotypes, rs2286194-rs3735520-rs17501108 (APL p=0.007403 for SPH and 0.062685 for SE) and rs12536657-rs2286194 (APL p=0.004219 for SPH and 0.00518 for SE), showed significant association with mild to moderate myopia versus emmetropia. A promising association between extreme high myopia and the HGF SNP, rs2286194, was also found (APL p=0.005763 for SPH and 0.004103 for SE). No evidence of association was found in the SNPs tested for C-MET., Conclusions: This study supports a strong association between the mild to moderate myopia group and the HGF SNP rs3735520 and the HGF haplotypes rs2286194-rs3735520-rs17501108 and rs12536657-rs2286194, and a moderate association of the extreme high myopia with rs2286194. C-MET polymorphism statistical associations with myopia in an Asian study were not replicated in our Caucasian cohort. HGF may be a potential myopia candidate gene for further investigation.

Purpose: Three previous studies have tested for an association between high myopia and polymorphisms in the open angle glaucoma gene, myocilin (MYOC), all in subjects of Chinese ethnicity. In two of the studies, a significant association was found while in the third, there was no association. We sought to investigate the association between high myopia and polymorphisms in MYOC in subjects of European ethnicity., Methods: Subjects were recruited from two sites, Cardiff University in the UK and Duke University in the United States. The Cardiff University cohort was comprised of 164 families with high myopia (604 subjects) plus 112 unrelated, highly myopic cases and 114 emmetropic controls. The Duke University cohort was comprised of 87 families with high myopia (362 subjects) plus 59 unrelated, highly myopic cases. Subject DNA was genotyped with a panel of MYOC single nucleotide polymorphisms (SNPs) including those found previously associated with high myopia. The Cardiff cohort was also genotyped for two flanking microsatellite markers analyzed in prior studies. Association between high myopia and MYOC polymorphisms was assessed using the Unphased program., Results: Since there was no evidence of heterogeneity in genotype frequencies between families and singleton samples or between cohorts, both subject groups (families and unrelated subjects) from both recruitment sites were analyzed jointly for those SNPs genotyped in common. Two variants showed significant association before correction for multiple testing. These two variants were rs16864720 (p=0.043) and NGA17 (p=0.026). However, there was no significant association after Bonferroni correction. The estimated relative risk (RR) conferred by each of the MYOC variants was low (RR<1.5)., Conclusions: Our results suggest that MYOC polymorphisms have a very low, or possibly negligible, influence on high myopia susceptibility in subjects of European ethnicity.

Purpose: Mutations in the SOX2 and CHX10 genes have been reported in patients with anophthalmia and/or microphthalmia. In this study, we evaluated 34 anophthalmic/microphthalmic patient DNA samples (two sets of siblings included) for mutations and sequence variants in SOX2 and CHX10., Methods: Conformational sensitive gel electrophoresis (CSGE) was used for the initial SOX2 and CHX10 screening of 34 affected individuals (two sets of siblings), five unaffected family members, and 80 healthy controls. Patient samples containing heteroduplexes were selected for sequence analysis. Base pair changes in SOX2 and CHX10 were confirmed by sequencing bidirectionally in patient samples., Results: Two novel heterozygous mutations and two sequence variants (one known) in SOX2 were identified in this cohort. Mutation c.310 G>T (p. Glu104X), found in one patient, was in the region encoding the high mobility group (HMG) DNA-binding domain and resulted in a change from glutamic acid to a stop codon. The second mutation, noted in two affected siblings, was a single nucleotide deletion c.549delC (p. Pro184ArgfsX19) in the region encoding the activation domain, resulting in a frameshift and premature termination of the coding sequence. The shortened protein products may result in the loss of function. In addition, a novel nucleotide substitution c.*557G>A was identified in the 3'-untranslated region in one patient. The relationship between the nucleotide change and the protein function is indeterminate. A known single nucleotide polymorphism (c. *469 C>A, SNP rs11915160) was also detected in 2 of the 34 patients. Screening of CHX10 identified two synonymous sequence variants, c.471 C>T (p.Ser157Ser, rs35435463) and c.579 G>A (p. Gln193Gln, novel SNP), and one non-synonymous sequence variant, c.871 G>A (p. Asp291Asn, novel SNP). The non-synonymous polymorphism was also present in healthy controls, suggesting non-causality., Conclusions: These results support the role of SOX2 in ocular development. Loss of SOX2 function results in severe eye malformation. CHX10 was not implicated with microphthalmia/anophthalmia in our patient cohort.

Purpose: The membrane-type frizzled-related protein (MFRP) gene is selectively expressed in the retinal pigment epithelium and ciliary body, and mutations of this gene cause nanophthalmos. The MFRP gene may not be essential for retinal function but has been hypothesized to play a role in ocular axial length regulation. The involvement of the MFRP gene in moderate to high hyperopic, isolated microphthalmic/anophthalmic, and high myopic patients was tested in two phases: a mutation screening/sequence variant discovery phase and a genetic association study phase., Methods: Eleven hyperopic, ten microphthalmic/anophthalmic, and seven non-syndromic high-grade myopic patients of varying ages and 11 control subjects participated in the mutation screening phase. Sixteen primer pairs were designed to amplify the 13 exons of the MFRP gene including intron/exon boundaries. Polymerase chain reactions were performed, and amplified products were sequenced using standard techniques. Normal and affected individual DNA sequences were compared alongside the known reference sequence (UCSC genome browser) for the MFRP gene. The genetic association study included 146 multiplex non-syndromic high-grade myopia families. Seventeen intragenic and flanking single nucleotide polymorphisms (SNPs) were chosen for the MFRP gene and genotyped in the large data set using the Taqman allelic discrimination assay. The family-based association Pedigree Disequilibrium Test (PDT) and GenoPDT were performed., Results: The average spherical refractive error of the hyperopic patient cohort was +4.21 diopters (D; range +2.00 to +9.25 D) and of the myopic patient cohort was -12.36 D (range -8.25 to -14.50 D). A total of 16 SNPs were identified by direct sequencing. No significant association was determined between the 16 MFRP gene SNPs and the moderate to high hyperopia, microphthalmia/anophthalmia affection status, and high myopia. Family based association analysis did not reveal any association between the 17 SNPs genotyped in the larger family data set for any refractive error type., Conclusions: Sequence variants of the MFRP gene do not appear to be associated with either the less severe forms of hyperopia, extreme forms of limited eye growth and development, or high myopia. These results indicate that the MFRP gene may not play a role in regulating ocular axial length in these phenotypes.

Purpose: Anophthalmia and microphthalmia (A/M) are rare congenital ocular malformations presenting with the absence of eye components or small eyes with or without structural abnormalities. A/M can be isolated or syndromic. The stimulated by retinoic acid gene 6 (STRA6) and Sloan-Kettering viral oncogene homolog (SKI) genes are involved in vitamin A metabolism, and are implicated with A/M developmental abnormalities in human and animal studies. Vitamin A metabolism is vital to normal eye development and growth. This study explores the association of these genes in a cohort of subjects with A/M., Methods: STRA6 and SKI were screened for sequence variants by direct sequencing of genomic DNA samples from 18 affected subjects with A/M. The DNA samples of 4 external, unrelated controls were initially screened. Eighty-nine additional unrelated controls were screened to confirm that any sequence variants found in the affected subject DNA samples were related to the phenotype. Coding regions, intron-exon boundaries, and untranslated regions were sequenced by standard techniques. Derived DNA sequences were compared to known reference sequences from public genomic databases., Results: For STRA6, a novel coding non-synonymous sequence variant was found in one subject, resulting in an amino acid change from glycine to glutamic acid in residue 217. One novel nonsense sequence variant found in the same subject changed the STRA6 amino acid residue 592 from cytosine to thymine resulting in a premature stop codon. For SKI, a known coding non-synonymous sequence variant (rs28384811) was found in 3 subject DNA samples and 11/89 control DNA samples. Four novel coding-synonymous sequence variants were observed in SKI., Conclusions: The STRA6 sequence variants reported in this study could play a role in the pathogenesis of A/M by structural changes to the STRA6 protein. We can attribute 4% A/M incidence in this cohort to these sequence variants. Although no SKI sequence variants were found in this cohort, SKI should not be ruled out as a candidate gene for A/M due to the small cohort size.

Purpose: Myopia is a common, complex disorder, and severe forms have implications for blindness due to increased risk of premature cataracts, glaucoma, retinal detachment, and macular degeneration. Autosomal dominant (AD) non-syndromic high-grade myopia has been mapped to chromosomes 18p11.31, 12q21-23, 17q21-23, 7q36, 2q37.1, 7p15.3, 15q12-13, 3q26, 4q12, 8p23, 4q22-q27, 1p36, and Xq23-q25. Here, we demonstrate evidence of linkage for AD non-syndromic high-grade myopia in a large Hutterite family to a locus on chromosome 10q21.1., Methods: After clinical evaluation, genomic DNA was genotyped from 29 members of a Hutterite family from South Dakota (7 affected). The average refractive error of affected individuals was -7.04 diopters. Microsatellite markers were used to exclude linkage to the known AD nonsyndromic high-grade myopia loci as well as to syndromic high-grade myopia loci. A genome screen was then performed using 382 markers with an average inter-marker distance of 10 cM followed by fine-point mapping in all regions of the genome that gave positive LOD scores. SimWalk2 software was used for multipoint linkage based on AD and autosomal recessive (AR) models with a penetrance of 90% and a disease allele frequency of 0.001., Results: A maximum multipoint LOD score of 3.22 was achieved under an AD model at microsatellite marker D10S1643. Fine point mapping and haplotype analysis defined a critical region of 2.67 cM on chromosome 10q21.1. Haplotype analysis demonstrated two distinct haplotypes segregating with high-grade myopia, indicative of two distinct mutations occurring in the same gene., Conclusions: We have identified a presumptive myopia locus for high-grade myopia based on linkage and haplotype analysis.

Purpose: Retinopathy of prematurity (ROP) is a leading cause of visual loss in the pediatric population. Mutations in the Norrie disease gene (NDP) are associated with heritable retinal vascular disorders, and have been found in a small subset of patients with severe retinopathy of prematurity. Varying rates of progression to threshold disease in different races may have a genetic basis, as recent studies suggest that the incidence of NDP mutations may vary in different groups. African Americans, for example, are less likely to develop severe degrees of ROP. We screened a large cohort of ethnically diverse patients for mutations in the entire NDP., Methods: A total of 143 subjects of different ethnic backgrounds were enrolled in the study. Fifty-four patients had severe ROP (Stage 3 or worse). Of these, 38 were threshold in at least one eye (with a mean gestational age of 26.1 weeks and mean birth weight of 788.4 g). There were 36 patients with mild or no ROP, 31 parents with no history of retinal disease or prematurity, and 22 wild type (normal) controls. There were 70 African American subjects, 55 Caucasians, and 18 of other races. Severe ROP was noted in 29 African American subjects, 17 Caucasians, and 8 of other races. Seven polymerase chain reaction primer pairs spanning the NDP were optimized for denaturing high performance liquid chromatography and direct sequencing. Three primer pairs covered the coding region, and the remaining four spanned the 3' and 5' untranslated regions (UTR)., Results: Six of 54 (11%) infants with severe ROP had polymorphisms in the NDP. Five of the infants were African American, and one was Caucasian. Two parents were heterozygous for the same polymorphism as their child. One parent-child pair had a single base pair (bp) insertion in the 3' UTR region. Another parent-child pair had two mutations: a 14 bp deletion in the 5' UTR region of exon 1 and a single nucleotide polymorphism in the 5' UTR region of exon 2. No coding region sequence changes were found. No polymorphisms were observed in infants with mild or no ROP, or in the wild type controls., Conclusions: Of the six sequence alterations found, five were novel nucleotide changes: One in the 5' UTR region of exon 2, and four in the 3' UTR region of exon 3. The extent of NDP polymorphisms in this large, racially diverse group of infants is moderate. NDP polymorphisms may play a role in the pathogenesis of ROP, but do not appear to be a major causative factor.

Purpose: Myopia is a common complex eye disorder, with implications for blindness due to increased risk of retinal detachment, chorioretinal degeneration, premature cataracts, and glaucoma. A genomic interval of 2.2 centiMorgans (cM) was defined on chromosome band 18p11.31 using 7 families diagnosed with autosomal dominant high myopia and was designated the MYP2 locus. To characterize this region, we analyzed 9 known candidate genes localized to within the 2.2 cM interval by direct sequencing., Methods: Using public databases, a physical map of the MYP2 interval was compiled. Gene expression studies in ocular tissues using complementary DNA library screens, microarray experiments, reverse transcription techniques, and expression data identified in external databases aided in prioritizing gene selection for screening. Coding regions, intron-exon boundaries and untranslated exons of all known genes [Clusterin-like 1 (CLUL1), elastin microfibril interfacer 2 (EMILIN2), lipin 2 (LPIN2), myomesin 1 (MYOM1), myosin regulatory light chain 3 (MRCL3), myosin regulatory light chain 2 (MRLC2), transforming growth beta-induced factor (TGIFbeta), large Drosophila homolog associated protein 1 (DLGAP1), and zinc finger protein 161 homolog (ZFP161)] were sequenced using genomic DNA samples from 9 affected and 6 unaffected MYP2 pedigree members, and from 5 external controls (4 unaffected and 1 affected). Gene sequence changes were compared to known variants from public single nucleotide polymorphism (SNP) databases., Results: In total, 103 polymorphisms were found by direct sequencing; 10 were missense, 14 were silent, 26 were not translated, 49 were intronic, 1 insertion, and 3 were homozygous deletions. Twenty-seven polymorphisms were novel. Novel SNPs were submitted to the public database; observed frequencies were submitted for known SNPs. No sequence alterations segregated with the disease phenotype., Conclusions: Mutation analysis of 9 encoded positional candidate genes on MYP2 loci did not identify sequence alterations associated with the disease phenotype. Further studies of MYP2 candidate genes, including analysis of putative genes predicted in silico, are underway.

Purpose: To determine the incidence of glaucoma following cataract surgery in children and to identify surgically modifiable risk factors that may influence the development of glaucoma in these eyes., Methods: All lensectomies performed in patients 18 years old or younger over a 7-year period (1995 through 2001) were identified by conducting a database search. A retrospective chart review was performed for every patient identified. Data extraction included patient's age at surgery, intraocular lens implantation at cataract extraction, date of glaucoma onset, and length of follow-up. Statistical methods included risk ratio calculations and Kaplan-Meier analyses for the "time to glaucoma" for eyes undergoing lensectomy., Results: We identified 116 eyes of 79 children in whom lensectomy was performed. The median age at cataract surgery was 178 days (approval 6 months). Mean follow-up time was 2.7 years. The overall incidence of glaucoma was 11%. Kaplan-Meier analysis demonstrated that eyes operated on at less than 30 days of age were statistically more likely to develop glaucoma than eyes operated on at age 30 days or older (P < .001). For those operated on at less than 30 days of age, the risk ratio was 11.8 for subsequent glaucoma development compared with those operated on at 30 days of age or older. Forty-nine eyes (42%) had primary intraocular lens implantation, and none of these developed glaucoma (P = .001)., Conclusions: Timing of surgery at less than 30 days of age and lack of implantation of an intraocular lens at lensectomy were both associated with an increased risk of subsequent glaucoma. Knowledge of modifiable risk factors is essential to allow ophthalmic surgeons to make cogent decisions regarding the care of children with cataracts.

Purpose: The proteoglycans lumican and fibromodulin regulate collagen fibril assembly and show expression in ocular tissues. A recent mouse knockout study implicates lumican and fibromodulin as functional candidate genes for high myopia. Lumican maps within the chromosome 12q21-q23 autosomal dominant high grade myopia-3 (MYP3) interval, and fibromodulin maps to chromosome 1q32. We screened individuals for lumican and fibromodulin sequence alterations from the original MYP3 family, and from a second high grade myopia pedigree that showed suggestive linkage to both the MYP3 interval and to chromosome 1q32., Methods: A total of 10 affected (average spherical refractive error was -16.13 D) and 5 unaffected individuals from the 2 families were screened by direct DNA sequencing. Six primer pairs spanning intron-exon boundaries and coding regions were designed for the 3-exon 1804 base pair (bp) lumican gene. Two primer pairs for the 2-exon 2863 bp fibromodulin gene were designed. Polymerase chain reaction products were sequenced and analyzed using standard fluorescent methods. Sequences were quality scored and aligned for polymorphic analysis., Results: Direct DNA sequencing of lumican amplicons yielded the expected sequence with no evidence of polymorphism or pathologic mutation. Sequencing of fibromodulin amplicons revealed 6 polymorphisms, 1 of which was novel. One polymorphism was a silent mutation, and five were in the 3' untranslated region. No polymorphism segregated with high myopia., Conclusions: Although null and double null Lum and Fmod mouse models have been developed for high myopia, our human cohort did not show affected status association with these genes. Sequencing of the human lumican and fibromodulin genes has excluded them as candidate genes for MYP3 associated high grade myopia.

Purpose: High myopia is a common complex-trait eye disorder, with implications for blindness due to increased risk of retinal detachment, macular degeneration, premature cataracts, and glaucoma. Mapping studies have identified at least four loci for nonsyndromic autosomal dominant high myopia at 18p11.31, 12q22-q23, 17q21-q23, and 7q36. The smallest haplotyped interval for these loci is that of the MYP2 locus on 18p11.31. Recently, the transforming growth beta-induced factor (TGIF) gene was reported to be a candidate gene for MYP2-associated high myopia in single-nucleotide polymorphism studies. The purpose of this study was to determine whether DNA sequence variants in the human TGIF gene are causally related to MYP2-associated high myopia., Methods: The protein coding regions and intron-exon boundaries of the human TGIF gene were sequenced using genomic DNA samples from MYP2 individuals (affected, unaffected) and external control subjects. The TGIF model used was the April 20, 2003, human genome National Center for Biotechnology Information (NCBI) build 33, which has 10 exons and encodes eight transcript variants. Polymorphic sequence changes were compared to those in the previous report. Reverse-transcription polymerase chain reaction (RT-PCR) was performed to validate TGIF gene expression in ocular tissues., Results: A total of 21 polymorphisms of TGIF were found by direct sequencing: 3 were missense, 2 were silent, 10 were not translated, 4 were intronic, and 2 were homozygous deletions. The 3 missense allelic variants were localized to exon 10 at positions 236C-->T(Pro-->Leu), 244C-->T(Pro-->Ser), and 245C-->T(Pro-->Leu). Silent mutations were observed in exon 10 at positions 177A-->G, 333C-->T. Ten polymorphisms were novel. No sequence alterations were exclusively associated with the affected disease phenotype. RT-PCR results confirmed expression of TGIF in RNA samples derived from human sclera, cornea, optic nerve, and retina., Conclusions: TGIF is a known candidate gene for MYP2-associated high myopia, based on its mapped location within the MYP2 interval. Mutation analysis of the encoded TGIF gene for MYP2 autosomal dominant high myopia did not identify sequence alterations associated with the disease phenotype. Further studies of MYP2 candidate genes are needed to determine the gene that causes of this potentially blinding disorder.

Purpose: To develop gene expression profiles of human sclera to allow for the identification of novel, uncharacterized genes in this tissue-type, and to identify candidate genes for scleral disorders., Methods: Total RNA was isolated from 6 donor sources of human sclerae, and reverse transcribed into cDNA using a T7-(dT) 24 primer. The resulting cDNA was in vitro transcribed to produce biotin-labeled cRNA, fragmented, and mixed with hybridization controls before a 16 h hybridization step with oligonucleotide probes on 6 Affymetrix U95A chips. The chips were scanned twice at 570 nM and the data collected using GeneChip software. Array analyses were carried out with Microarray Suite, version 5.0 (Affymetrix), using the expression analysis algorithm to run an absolute analysis after cell intensities were computed. All arrays were scaled to the same target intensity using all probe sets. Reverse-transcription polymerase chain reaction (RT-PCR) was performed to validate the microarray results., Results: There were 3,751 genes with "present" calls assigned independently to all six human scleral samples. These genes could be clustered into 4 major categories; transcription (10%), metabolism (8.8%), cell growth and proliferation (5.4%), and extracellular matrix (2%). Many extracellular matrix proteins, such as collagens 6A3 and 10A1, thrombospondins 2 and 4, and dystroglycan have not previously been shown to be expressed in sclera. RT-PCR results confirmed scleral expression in 7 extracellular matrix genes examined., Conclusions: This study demonstrated the utility of gene microarray technology in identifying global patterns of scleral gene expression, and provides an extended list of genes expressed in human sclera. Identification of genes expressed in sclera contributes to our understanding of scleral biology, and potentially provides positional candidate genes for scleral disorders such as high myopia.

Purpose: Despite the plethora of experimental myopia animal studies that demonstrate biochemical factor changes in various eye tissues, and limited human studies utilizing pharmacologic agents to thwart axial elongation, we have little knowledge of the basic physiology that drives myopic development. Identifying the implicated genes for myopia susceptibility will provide a fundamental molecular understanding of how myopia occurs and may lead to directed physiologic (ie, pharmacologic, gene therapy) interventions. The purpose of this proposal is to describe the results of positional candidate gene screening of selected genes within the autosomal dominant high-grade myopia-2 locus (MYP2) on chromosome 18p11.31., Methods: A physical map of a contracted MYP2 interval was compiled, and gene expression studies in ocular tissues using complementary DNA library screens, microarray matches, and reverse-transcription techniques aided in prioritizing gene selection for screening. The TGIF, EMLIN-2, MLCB, and CLUL1 genes were screened in DNA samples from unrelated controls and in high-myopia affected and unaffected family members from the original seven MYP2 pedigrees. All candidate genes were screened by direct base pair sequence analysis., Results: Consistent segregation of a gene sequence alteration (polymorphism) with myopia was not demonstrated in any of the seven families. Novel single nucleotide polymorphisms were found., Conclusion: The positional candidate genes TGIF, EMLIN-2, MLCB, and CLUL1 are not associated with MYP2-linked high-grade myopia. Base change polymorphisms discovered with base sequence screening of these genes were submitted to an Internet database. Other genes that also map within the interval are currently undergoing mutation screening.

Purpose: Clones established from a human scleral cDNA library were systematically sequenced. Public database sequence comparisons were performed to generate a profile of genes expressed in the human sclera and identify candidate genes for inherited diseases with scleral involvement., Methods: A directionally cloned pCMV-PCR cDNA library was constructed from RNA isolated from scleras of human donor eyes with known plano refractive history. Plasmid DNA was extracted from randomly selected cDNA clones, and the insert sequences were determined by 5' end single-pass sequencing. Expressed sequence tags (ESTs) were generated and analyzed with the GenBank BLASTN program to identify sequence homologies to known genes., Results: A total of 609 ESTs underwent BLAST analysis. Of these, 341 (56%) matched 228 known human genes and 4 non-human genes, 252 matched uncharacterized ESTs, and 16 showed no significant homology to human or non-human known sequences. The most redundant connective tissue-related genes were alphaA-crystalline, Xalpha-1 collagen, and beta-5 integrin. Other extracellular matrix gene matches were biglycan, syndecan, decorin, fibromodulin, proline arginine-rich end leucine-rich repeat protein, transgelin, TIMP-1, and fibulin 1. Human scleral expression of all but decorin and biglycan has not previously been reported., Conclusions: This effort provides the first partial list of genes expressed in human sclera. Identification of genes expressed in the sclera contributes to our understanding of scleral biology, and potentially provides positional candidate genes for scleral disorders such as high myopia.