Uveal coloboma: clinical and basic science update

Homozygosity for a hypomorphic mutation in frizzled class receptor 5 causes syndromic ocular coloboma with microcornea in humans

Ocular coloboma (OC) is a congenital disorder caused by the incomplete closure of the embryonic ocular fissure. OC can present as a simple anomaly or, in more complex forms, be associated with additional ocular abnormalities. It can occur in isolation or as part of a broader syndrome, exhibiting considerable genetic heterogeneity. Diagnostic yield for OC remains below 30%, indicating the need for further genetic exploration. Mutations in the Wnt receptor FZD5, which is expressed throughout eye development, have been linked to both isolated and complex forms of coloboma. These mutations often result in a dominant-negative effect, where the mutated FZD5 protein disrupts WNT signaling by sequestering WNT ligands. Here, we describe a case of syndromic bilateral OC with additional features such as microcornea, bone developmental anomalies, and mild intellectual disability. Whole exome sequencing revealed a homozygous rare missense variant in FZD5. Consistent with a loss-of-function effect, overexpressing of fzd5 mRNA harboring the missense variant in zebrafish embryos does not influence embryonic development, whereas overexpression of wild-type fzd5 mRNA results in body axis duplications. However, in vitro TOPFlash assays revealed that the missense variant only caused partial loss-of-function, behaving as a hypomorphic mutation. We further showed that the mutant protein still localized to the cell membrane and maintained proper conformation when modeled in silico, suggesting that the impairment lies in signal transduction. This hypothesis is further supported by the fact that the variant affects a highly conserved amino acid known to be crucial for protein-protein interactions.

Epidemiology of Coloboma: Prevalence and Patterns in Texas, 1999-2014

BACKGROUND

Coloboma is a rare congenital malformation in which part of the tissue that makes up the eye is missing and may cause visual impairment or blindness. Little is known about the epidemiology of this condition. Therefore, we obtained data from the Texas Birth Defects Registry on children identified with coloboma for the period 1999-2014.

METHODS

Using information on all live births from the same period, prevalence ratios (PRs) for selected demographic and clinical factors were used to estimate associations using Poisson regression among cases with coloboma. Coloboma cases were divided into subgroups to explore patterns of co-occurring defects and syndromes. All variables significant in unadjusted models (p < 0.05) were included in multivariable models to evaluate adjusted PRs (aPRs).

RESULTS

We identified 1587 cases with coloboma, of whom 934 (58.8%) were nonsyndromic, and 474 (29.9%) were isolated. When considering all identified cases, factors associated with significant differences in prevalence included plurality (multiple vs. singleton aPR = 1.4, 95% CI: 1.1-1.8); maternal education (college or greater vs. less than high school aPR = 0.7, 95% CI: 0.6-0.9); maternal race/ethnicity (Hispanic vs. non-Hispanic White aPR = 0.9, 95% CI: 0.8-1.0); and maternal diabetes (yes vs. no aPR = 1.3, 95% CI: 1.0-1.6). There was a notable increase in the birth prevalence of coloboma during the study period (p-for-trend < 0.001). Effect estimates were similar across the different subgroups.

CONCLUSION

In our large population, we identified several factors associated with the prevalence of coloboma. These findings may help define subgroups of women more likely to have children affected by coloboma, which could inform improved screening efforts.

Increased Netrin downstream of overactive Hedgehog signaling disrupts optic fissure formation

BACKGROUND

Uveal coloboma, a developmental eye defect, is caused by failed development of the optic fissure, a ventral structure in the optic stalk and cup where axons exit the eye and vasculature enters. The Hedgehog (Hh) signaling pathway regulates optic fissure development: loss-of-function mutations in the Hh receptor ptch2 produce overactive Hh signaling and can result in coloboma. We previously proposed a model where overactive Hh signaling disrupts optic fissure formation by upregulating transcriptional targets acting both cell- and non-cell-autonomously. Here, we examine the Netrin family of secreted ligands as candidate Hh target genes.

RESULTS

We find multiple Netrin ligands upregulated in the zebrafish ptch2 mutant during optic fissure development. Using a gain-of-function approach to overexpress Netrin in a spatiotemporally specific manner, we find that netrin1a or netrin1b overexpression is sufficient to cause coloboma and disrupt wild-type optic fissure formation. We used loss-of-function alleles, CRISPR/Cas9 mutagenesis, and morpholino knockdown to test if loss of Netrin can rescue coloboma in the ptch2 mutant: loss of netrin genes does not rescue the ptch2 mutant phenotype.

CONCLUSION

These results suggest that Netrin is sufficient but not required to disrupt optic fissure formation downstream of overactive Hh signaling in the ptch2 mutant.

Uveal colobomas with pseudo-duplication of the optic disc in both eyes: imaging by ultra-widefield swept-source optical coherence tomography angiography: a case report

BACKGROUND

Duplication of the optic disc is a rare phenomenon. Differentiating between true duplication and pseudo-duplication requires a comprehensive set of diagnostic procedures. Advancements in imaging provide new insights into this condition.

CASE PRESENTATION

This report details a unique case involving an 8-year-old Han Chinese girl diagnosed with uveal colobomas and pseudo-duplication of the optic disc in both eyes. The extensive multimodal examination included assessments of vision, fundus examination, fundus photography, B-scan ultrasonography, ultra-widefield swept-source optical coherence tomography angiography, fundus fluorescein angiography, fundus autofluorescence, and magnetic resonance imaging.

CONCLUSION

Ultra-widefield swept-source optical coherence tomography angiography proves to be a vital tool for examining and monitoring uveal colobomas with pseudo-duplication of the optic disc.

Increased Netrin downstream of overactive Hedgehog signaling disrupts optic fissure formation

Background

Uveal coloboma, a developmental eye defect, is caused by failed development of the optic fissure, a ventral structure in the optic stalk and cup where axons exit the eye and vasculature enters. The Hedgehog (Hh) signaling pathway regulates optic fissure development: loss-of-function mutations in the Hh receptor ptch2 produce overactive Hh signaling and can result in coloboma. We previously proposed a model where overactive Hh signaling disrupts optic fissure formation by upregulating transcriptional targets acting both cell- and non-cell-autonomously. Here, we examine the Netrin family of secreted ligands as candidate Hh target genes.

Results

We find multiple Netrin ligands upregulated in the zebrafish ptch2 mutant during optic fissure development. Using a gain-of-function approach to overexpress Netrin in a spatiotemporally specific manner, we find that netrin1a or netrin1b overexpression is sufficient to cause coloboma and disrupt wild-type optic fissure formation. We used loss-of-function alleles, CRISPR/Cas9 mutagenesis, and morpholino knockdown to test if loss of Netrin can rescue coloboma in the ptch2 mutant: loss of netrin genes does not rescue the ptch2 mutant phenotype.

Conclusion

These results suggest that Netrin is sufficient but not required to disrupt optic fissure formation downstream of overactive Hh signaling in the ptch2 mutant.

A case report of retinal dystrophy in patients with PACS1 syndrome

PACS1 syndrome, also referred to as Schuurs-Hoeijmakers syndrome, is a multisystemic developmental disorder caused by a specific pathogenic variant in the PACS1 (phosphofurin acidic cluster sorting protein 1) gene. Ocular findings in PACS1 syndrome are known to include iris, retina, optic nerve coloboma, myopia, nystagmus, and strabismus. Here, we present the cases of two patients referred to the University of Wisconsin-Madison Department of Ophthalmology and Visual Sciences for ocular evaluation. The first patient is a 14-month-old female who, at 3 months of age, was found to have a depressed rod and cone response on electroretinogram (ERG), consistent with possible retinal dystrophy (RD). This feature has not been previously described in PACS1 syndrome and joins a growing list of calls for expanding the PACS1 phenotype. The second case illustrates a 5-year-old male referred for ocular screening after diagnosing PACS1 syndrome and underwent ERG without abnormal findings. These cases demonstrate the significant variability in the ophthalmic presentation of PACS1 syndrome and the need for early screening. These novel findings may have implications in understanding the mechanism of the PACS1 protein and its role in retinal ciliary phototransduction in photoreceptors.

Eye Morphogenesis in Vertebrates

Proper eye structure is essential for visual function: Multiple essential eye tissues must take shape and assemble into a precise three-dimensional configuration. Accordingly, alterations to eye structure can lead to pathological conditions of visual impairment. Changes in eye shape can also be adaptive over evolutionary time. Eye structure is first established during development with the formation of the optic cup, which contains the neural retina, retinal pigment epithelium, and lens. This crucial yet deceptively simple hemispherical structure lays the foundation for all later elaborations of the eye. Building on descriptions of the embryonic eye that started with hand drawings and micrographs, the field is beginning to identify mechanisms driving dynamic changes in three-dimensional cell and tissue shape. A combination of molecular genetics, imaging, and pharmacological approaches is defining connections among transcription factors, signaling pathways, and the intracellular machinery governing the emergence of this crucial structure.

A novel variant affecting the cytoplasmic tail of the FAT1 protocadherin causing coloboma and renal failure: A case report

BACKGROUND

Variations in the protocadherin gene FAT1 have recently been associated with a syndrome that includes coloboma, facial dysmorphism, renal failure, syndactyly, and other developmental defects.

MATERIALS AND METHODS

Detailed medical and family history, physical examination, and molecular analysis.

RESULTS

This non-dysmorphic, intellectually normal 51-year-old woman presented with bilateral colobomata and renal failure of unclear etiology, and asymmetric sensorineural hearing loss. Family history was notable for multiple family members with various forms of cancer. Whole exome sequencing revealed a homozygous frame shift variant in FAT1, predicted to truncate the FAT1 protein at the furthest position in the protein structure published to date in a patient with coloboma.

CONCLUSIONS

This case provides further evidence of the pleiotropic effects of FAT1 in optic fissure closure and kidney function. Also, because this variant is in the last exon, it would be anticipated to escape nonsense-mediated decay, opening the possibility that the protein is made and expressed, but not completely functional, as its intracellular domain is truncated.

Eyes on CHARGE syndrome: Roles of CHD7 in ocular development

The development of the vertebrate visual system involves complex morphogenetic interactions of cells derived from multiple embryonic lineages. Disruptions in this process are associated with structural birth defects such as microphthalmia, anophthalmia, and coloboma (collectively referred to as MAC), and inherited retinal degenerative diseases such as retinitis pigmentosa and allied dystrophies. MAC and retinal degeneration are also observed in systemic congenital malformation syndromes. One important example is CHARGE syndrome, a genetic disorder characterized by coloboma, heart defects, choanal atresia, growth retardation, genital abnormalities, and ear abnormalities. Mutations in the gene encoding Chromodomain helicase DNA binding protein 7 (CHD7) cause the majority of CHARGE syndrome cases. However, the pathogenetic mechanisms that connect loss of CHD7 to the ocular complications observed in CHARGE syndrome have not been identified. In this review, we provide a general overview of ocular development and congenital disorders affecting the eye. This is followed by a comprehensive description of CHARGE syndrome, including discussion of the spectrum of ocular defects that have been described in this disorder. In addition, we discuss the current knowledge of CHD7 function and focus on its contributions to the development of ocular structures. Finally, we discuss outstanding gaps in our knowledge of the role of CHD7 in eye formation, and propose avenues of investigation to further our understanding of how CHD7 activity regulates ocular and retinal development.

Isolated Chorioretinal Coloboma: A Case Report

Ocular coloboma is a rare congenital anomaly that arises due to an abnormality in embryogenesis. It occurs due to failed fusion of the embryonic fissure resulting in a persistent defect. Colobomas may present with vision loss but are most commonly asymptomatic and diagnosed incidentally. In this article, we present a case of asymptomatic chorioretinal coloboma diagnosed on routine screening. The patient was managed with prophylactic argon laser retinopexy to prevent complications leading to visual impairment in the future.

De novo frameshift mutation in YAP1 associated with bilateral uveal coloboma and microphthalmia

BACKGROUND

Uveal colobomata are eye defects that result from failure of the optic fissure of the neuroectoderm-derived optic cup to close between weeks 5-7 of fetal life. Mutations in YAP1 have previously been linked to uveal coloboma. We present the clinical features and genetic basis of a one-year-old male with bilateral uveal colobomata.

MATERIALS AND METHODS

Clinical features were gathered from an age-appropriate evaluation and retrospectively from clinical records. DNA samples were collected from the proband, his uncle (who also had coloboma), both parents, and one sibling. Whole-genome sequencing of the coding regions and intron-exon boundaries confirmed a mutation in the proband. These genetic findings were verified using the Sanger method of DNA sequencing.

RESULTS

The proband is a male with congenital bilateral colobomata (iris/retina/nerve), reduced vision, nystagmus with null point, bilateral microcornea, right microphthalmia, possible mild right hemifacial microsomia, a tubular nose, possible spina bifida occulta, and astigmatism. Whole-genome sequencing confirmed a heterozygous YAP1 frameshift mutation NM_001130145.3:c.178dupG p.(Asp60GlyfsTer52) in the proband. This mutation was absent in all other tested family members.

CONCLUSIONS

We report a de novo mutation in YAP1 that likely results in nonsense-mediated decay. Given the association with YAP1 haploinsufficiency and colobomatous microphthalmia, this novel variant provides a molecular diagnosis for the proband. Further insight into YAP1 mutations may have implications in the prevention/treatment of uveal coloboma and other syndromic disorders.

Microcornea, iris and choroidal coloboma, and global developmental delay caused by TENM3 pathogenic variants in a Chinese patient

Background

Biallelic TENM3 pathogenic variants cause isolated or syndromic microphthalmia. Syndromic microphthalmia 15 (MCOPS15) is characterized by microphthalmia, coloboma, and developmental delay. Currently, only four cases of MCOPS15 have been reported and the clinical features varied among the patients indicating potential broad phenotypic spectrum.

Methods

The present case was a 6‐month‐old male at diagnosis. The patient exhibited long philtrum, large ears, bilateral ptosis, and nystagmus. Ophthalmic tests showed that he had microcornea, iris and choroidal coloboma. The patient presented with global developmental delay (GDD). Trio‐whole exome sequencing and genome copy number sequencing were conducted to explore the disease‐causing mutations.

Results

Exome sequencing and genome copy number sequencing showed the presence of L1471F and E661G compound mutations in TENM3, which were inherited from the mother and father, respectively. Sanger sequencing was conducted to verify association of the mutations with the disease in the present family.

Conclusion

Two TENM3 variants were identified in a patient with Syndromic microphthalmia 15 in the present study. However, further studies should be conducted to explore the pathogenicity of the variants.

Clinical and Demographic Profile of Uveal Coloboma: A hospital-based Study of 14,371 eyes of 9557 Indian Patients

OBJECTIVE

To describe the demographics and clinical profile of uveal coloboma in patients presenting to a multi-tier ophthalmology hospital network in India.

DESIGN

Cross- sectional hospital -based study.

METHODS

This cross-sectional hospital-based study included 2,817,766 new patients presenting between August 2010 and May 2021. Patients with a clinical diagnosis of uveal coloboma in at least one eye were included as cases. The data were collected using an electronic medical record system.

RESULTS

Overall, 9,557 (0.34%) patients were diagnosed with uveal coloboma. Just over half of the patients were male (51.82%) and had bilateral (50.37%) affliction. The most common age group at presentation was during the second decade of life with 2,198 (23%) patients. The overall prevalence was higher in patients from a lower socio-economic status (0.53%) and presenting from the rural geography (0.39%). The most common type was retino-choroidal coloboma in 8,049 (84.22%) patients followed by iris coloboma in 2,129 (22.28%) patients. The most common Ida Mann classification in the eyes with retino-choroidal coloboma was type 4 in 7,049 (57.23%) eyes followed by type 2 in 3,685 (29.92%) eyes. In the 14,371 eyes, 5,696 (39.64%) eyes had a visual impairment of blindness (>20/400) followed by mild or no visual impairment (<20/70) in 2,875 (20.01%) eyes. In the 2,228 (15.5%) eyes that required a surgical/ laser intervention, cataract surgery was performed in 951 (6.62%) eyes, vitreo-retinal surgery in 661 (4.6%) eyes followed by laser photocoagulation in 357 (2.48%) eyes.

CONCLUSION

Uveal Coloboma is more common in males, is predominantly bilateral in the population studied. It is more commonly found in patients from lower socio-economic strata and from a rural background. The most common type is retino-choroidal coloboma and over a third of the eyes are affected with blindness.

Loss of zebrafish dzip1 results in inappropriate recruitment of periocular mesenchyme to the optic fissure and ocular coloboma

Cilia are essential for the development and function of many different tissues. Although cilia machinery is crucial in the eye for photoreceptor development and function, a role for cilia in early eye development and morphogenesis is still somewhat unclear: many zebrafish cilia mutants retain cilia at early stages due to maternal deposition of cilia components. An eye phenotype has been described in the mouse Arl13 mutant, however, zebrafish arl13b is maternally deposited, and an early role for cilia proteins has not been tested in zebrafish eye development. Here we use the zebrafish dzip1 mutant, which exhibits a loss of cilia throughout stages of early eye development, to examine eye development and morphogenesis. We find that in dzip1 mutants, initial formation of the optic cup proceeds normally, however, the optic fissure subsequently fails to close and embryos develop the structural eye malformation ocular coloboma. Further, neural crest cells, which are implicated in optic fissure closure, do not populate the optic fissure correctly, suggesting that their inappropriate localization may be the underlying cause of coloboma. Overall, our results indicate a role for dzip1 in proper neural crest localization in the optic fissure and optic fissure closure.

Astrocyte-intrinsic and -extrinsic Fat1 activities regulate astrocyte development and angiogenesis in the retina

Angiogenesis is a stepwise process leading to blood vessel formation. In the vertebrate retina, endothelial cells are guided by astrocytes migrating along the inner surface, and the two processes are coupled by a tightly regulated cross-talks between the two cell types. Here, I have investigated how the FAT1 cadherin, a regulator of tissue morphogenesis that governs tissue cross-talk, influences retinal vascular development. Late-onset Fat1 inactivation in the neural lineage in mice, by interfering with astrocyte progenitor migration polarity and maturation, delayed postnatal retinal angiogenesis, leading to persistent vascular abnormalities in adult retinas. Impaired astrocyte migration and polarity were not associated with alterations of retinal ganglion cell axonal trajectories or of the inner limiting membrane. In contrast, inducible Fat1 ablation in postnatal astrocytes was sufficient to alter their migration polarity and proliferation. Altogether, this study uncovers astrocyte-intrinsic and -extrinsic Fat1 activities that influence astrocyte migration polarity, proliferation and maturation, disruption of which impacts retinal vascular development and maintenance.

Review of Evidence for Environmental Causes of Uveal Coloboma

Uveal coloboma is a condition defined by missing ocular tissues and is a significant cause of childhood blindness. It occurs from a failure of the optic fissure to close during embryonic development,and may lead to missing parts of the iris, ciliary body, retina, choroid, and optic nerve. Because there is no treatment for coloboma, efforts have focused on prevention. While several genetic causes of coloboma have been identified, little definitive research exists regarding the environmental causes of this condition. We review the current literature on environmental factors associated with coloboma in an effort to guide future research and preventative counseling related to this condition.

Ocular Coloboma With Choroidal Neovascular Membrane: A Case Report

Ocular coloboma (OC) is a rare congenital anomaly and a product of a defect in embryogenesis. It is the result of fetal fissure closure error that ends with a persistent cleft. Colobomas are generally accompanied by visual loss. In this article, we present a case of bilateral iris, disc, and retina coloboma that was managed with an anti-vascular endothelial growth factor (ranibizumab), and as a result, caused regression of the choroidal neovascular membranes and improved the patient's visual acuity. However, The patient will need lifelong follow-up to catch any retinochoroidal changes or development of cataract or glaucoma.

Pax2a, but not pax2b, influences cell survival and periocular mesenchyme localization to facilitate zebrafish optic fissure closure

Background

Pax2 is required for optic fissure development in many organisms, including humans and zebrafish. Zebrafish loss‐of‐function mutations in pax2a display coloboma, yet the etiology of the morphogenetic defects is unclear. Further, pax2 is duplicated in zebrafish, and a role for pax2b in optic fissure development has not been examined.

Results

Using a combination of imaging and molecular genetics, we interrogated a potential role for pax2b and examined how loss of pax2 affects optic fissure development. Although optic fissure formation appears normal in pax2 mutants, an endothelial‐specific subset of periocular mesenchyme (POM) fails to initially localize within the optic fissure, yet both neural crest and endothelial‐derived POM ectopically accumulate at later stages in pax2a and pax2a; pax2b mutants. Apoptosis is not up‐regulated within the optic fissure in pax2 mutants, yet cell death is increased in tissues outside of the optic fissure, and when apoptosis is inhibited, coloboma is partially rescued. In contrast to pax2a, loss of pax2b does not appear to affect optic fissure morphogenesis.

Conclusions

Our results suggest that pax2a, but not pax2b, supports cell survival outside of the optic fissure and POM abundance within it to facilitate optic fissure closure.

Zebrafish pax2a null mutants display a defect in optic fissure closure and coloboma

Loss of pax2b does not affect optic fissure development

An endothelial‐specific subset of periocular mesenchyme cells fails to initially localize to the optic fissure in pax2a mutants

At a later stage of optic fissure development both neural crest and endothelial‐derived periocular mesenchyme ectopically accumulate within the optic fissure

Pax2a mutants have increased apoptosis in surrounding tissues, but not within the optic fissure margin cells, and apoptosis in part underlies the coloboma phenotype

Wide-field choroidal thickness and vascularity index in myopes and emmetropes

PURPOSE

To study regional variations in choroidal thickness (CT), luminal thickness and stromal thickness of the choroid, and choroidal vascularity index (CVI) in low myopic and emmetropic eyes using wide-field optical coherence tomography (OCT).

METHODS

Sixty-nine healthy young adults between 20 and 38 years of age participated in this study, including 40 low myopes (mean ± SD spherical equivalent (MSE) refractive error: -3.00 ± 1.39 D, range: -6.00 to -0.62 D) and 29 emmetropes (MSE: -0.05 ± 0.09 D, range: -0.25 to +0.12 D). Wide-field CT, luminal thickness, stromal thickness and CVI were measured across five eccentricities (fovea, parafovea, perifovea; near-periphery and periphery) and four quadrants (nasal, temporal, inferior and superior), in vertical and horizontal meridians, while controlling for a range of extraneous factors potentially influencing the CT. Custom-written software was used to segment and binarize the OCT images.

RESULTS

Wide-field CT, luminal thickness and stromal thickness, averaged across all participants, exhibited significant topographical variation, with the foveal (379 ± 8 µm, 200 ± 4 µm, 179 ± 4 µm, respectively) and peripheral (275 ± 8 µm, 161 ± 4 µm, 114 ± 4 µm, respectively) regions presenting the thickest and thinnest regions (all p < 0.001). Wide-field CVI showed a progressively higher percentage (greater vascularity) with increasing eccentricity from the fovea towards the periphery (p < 0.001). Macular CT and stromal choroidal thickness were significantly thinner in myopes compared to emmetropes (p < 0.05). Myopes (55.7 ± 0.3%) showed a slightly higher CVI compared with emmetropes (54.4 ± 0.4%) (p < 0.05).

CONCLUSIONS

Low myopia in young adults was associated with significant choroidal thinning across the macular, but not extramacular regions, with this decrease in choroidal thickness mostly attributed to thinning in the stromal component of the choroid, rather than the luminal (vascular) component.

Radiology of Abnormal Globe Contour

The orbits are easily identified on routine computed tomography (CT) and magnetic resonance imaging (MRI) imaging of the head and neck. Although there are many structures within the orbits, the overall structure of the globe is the most noticeable and can be an important source for pathology. In particular, many disease processes alter globe morphology and it is imperative that the radiologist be aware of not only the most common, but uncommon etiologies as well. This article provides an image-rich review of the wide range of emergent and non-emergent pathology that can result in altered globe contour.

Ocular coloboma-a comprehensive review for the clinician

Typical ocular coloboma is caused by defective closure of the embryonal fissure. The occurrence of coloboma can be sporadic, hereditary (known or unknown gene defects) or associated with chromosomal abnormalities. Ocular colobomata are more often associated with systemic abnormalities when caused by chromosomal abnormalities. The ocular manifestations vary widely. At one extreme, the eye is hardly recognisable and non-functional—having been compressed by an orbital cyst, while at the other, one finds minimalistic involvement that hardly affects the structure and function of the eye. In the fundus, the variability involves the size of the coloboma (anteroposterior and transverse extent) and the involvement of the optic disc and fovea. The visual acuity is affected when coloboma involves disc and fovea, or is complicated by occurrence of retinal detachment, choroidal neovascular membrane, cataract, amblyopia due to uncorrected refractive errors, etc. While the basic birth anomaly cannot be corrected, most of the complications listed above are correctable to a great extent. Current day surgical management of coloboma-related retinal detachments has evolved to yield consistently good results. Cataract surgery in these eyes can pose a challenge due to a combination of microphthalmos and relatively hard lenses, resulting in increased risk of intra-operative complications. Prophylactic laser retinopexy to the border of choroidal coloboma appears to be an attractive option for reducing risk of coloboma-related retinal detachment. However, a majority of the eyes have the optic disc within the choroidal coloboma, thus making it difficult to safely administer a complete treatment.

A Systematic Review of the Clinical Manifestations and Diagnostic Methods for Macular Coloboma

Objectives: To present the clinical features of and diagnostic methods used for macular coloboma (MC), and to analyze the factors associated with best-corrected visual acuity (BCVA) in patients with MC.Methods: A systematic review using the MEDLINE (PubMed), EMBASE, LILACS, and Cochrane databases was performed. The factors associated with BCVA were analyzed.Results: A total of 21 patients (mean age at diagnosis, 18.1 ± 14.6 years) with 36 eyes affected by MC (5 unilateral, 16 bilateral) were included in the study. All 21 patients (100%) had undergone a good-quality fundus examination. The size of the MC lesions ranged from 1.0 × 1.2 to 4.0 × 4.0 disc diameters (DD). Twenty-seven (73%) eyes had pigmented MC, seven (19%) had non-pigmented MC, and one (3%) had an unspecific type. The diagnosis was confirmed using spectral-domain optical coherence tomography (SD-OCT) in 16 (43.2%) eyes. A positive correlation was found between BCVA and the type of MC (β = 0.876, p = .006) and abnormal eye movement (β = 0.087, p = .018), and a negative correlation was found between BCVA and a contributory medical history of ventricular septal defect (β = -0.327, p = .001).Conclusions: Pigmented MC was the most common type and had the highest possibility of causing impaired vision in the affected eyes. Additionally, joint examinations should be applied for diagnostic confirmation of MC. Furthermore, fundoscopy, electroretinogram, electrooculography, fundus fluorescein angiography, and SD-OCT are all critical for differential diagnosis of MC-like lesions.

Closing the Gap: Mechanisms of Epithelial Fusion During Optic Fissure Closure

A key embryonic process that occurs early in ocular development is optic fissure closure (OFC). This fusion process closes the ventral optic fissure and completes the circumferential continuity of the 3-dimensional eye. It is defined by the coming together and fusion of opposing neuroepithelia along the entire proximal-distal axis of the ventral optic cup, involving future neural retina, retinal pigment epithelium (RPE), optic nerve, ciliary body, and iris. Once these have occurred, cells within the fused seam differentiate into components of the functioning visual system. Correct development and progression of OFC, and the continued integrity of the fused margin along this axis, are important for the overall structure of the eye. Failure of OFC results in ocular coloboma-a significant cause of childhood visual impairment that can be associated with several complex ocular phenotypes including microphthalmia and anterior segment dysgenesis. Despite a large number of genes identified, the exact pathways that definitively mediate fusion have not yet been found, reflecting both the biological complexity and genetic heterogeneity of the process. This review will highlight how recent developmental studies have become focused specifically on the epithelial fusion aspects of OFC, applying a range of model organisms (spanning fish, avian, and mammalian species) and utilizing emerging high-resolution live-imaging technologies, transgenic fluorescent models, and unbiased transcriptomic analyses of segmentally-dissected fissure tissue. Key aspects of the fusion process are discussed, including basement membrane dynamics, unique cell behaviors, and the identities and fates of the cells that mediate fusion. These will be set in the context of what is now known, and how these point the way to new avenues of research.

Whole Exome Sequencing in Coloboma/Microphthalmia: Identification of Novel and Recurrent Variants in Seven Genes

Coloboma and microphthalmia (C/M) are related congenital eye malformations, which can cause significant visual impairment. Molecular diagnosis is challenging as the genes associated to date with C/M account for only a small percentage of cases. Overall, the genetic cause remains unknown in up to 80% of patients. High throughput DNA sequencing technologies, including whole-exome sequencing (WES), are therefore a useful and efficient tool for genetic screening and identification of new mutations and novel genes in C/M. In this study, we analyzed the DNA of 19 patients with C/M from 15 unrelated families using singleton WES and data analysis for 307 genes of interest. We identified seven novel and one recurrent potentially disease-causing variants in CRIM1, CHD7, FAT1, PTCH1, PUF60, BRPF1, and TGFB2 in 47% of our families, three of which occurred de novo. The detection rate in patients with ocular and extraocular manifestations (67%) was higher than in patients with an isolated ocular phenotype (46%). Our study highlights the significant genetic heterogeneity in C/M cohorts and emphasizes the diagnostic power of WES for the screening of patients and families with C/M.

Nf2 fine-tunes proliferation and tissue alignment during closure of the optic fissure in the embryonic mouse eye

Uveal coloboma represents one of the most common congenital ocular malformations accounting for up to 10% of childhood blindness (~1 in 5000 live birth). Coloboma originates from defective fusion of the optic fissure (OF), a transient gap that forms during eye morphogenesis by asymmetric, ventral invagination. Genetic heterogeneity combined with the activity of developmentally regulated genes suggests multiple mechanisms regulating OF closure. The tumor suppressor and FERM domain protein Neurofibromin 2 (NF2) controls diverse processes in cancer, development and regeneration, via Hippo pathway and cytoskeleton regulation. In humans, NF2 mutations can cause ocular abnormalities, including coloboma, however, its actual role in OF closure is unknown. Using conditional inactivation in the embryonic mouse eye, our data indicate that loss of Nf2 function results in a novel underlying cause for coloboma. In particular, mutant eyes show substantially increased retinal pigmented epithelium (RPE) proliferation in the fissure region with concomitant acquisition of RPE cell fate. Cells lining the OF margin can maintain RPE fate ectopically and fail to transition from neuroepithelial to cuboidal shape. In the dorsal RPE of the optic cup, Nf2 inactivation leads to a robust increase in cell number, with local disorganization of the cytoskeleton components F-actin and pMLC2. We propose that RPE hyperproliferation is the primary cause for the observed defects causing insufficient alignment of the OF margins in Nf2 mutants and failure to fuse properly, resulting in persistent coloboma. Our findings indicate that limiting proliferation particularly in the RPE layer is a critical mechanism during OF closure.

Ocular coloboma: Genetic variants reveal a dynamic model of eye development

Ocular coloboma is a congenital disorder of the eye where a gap exists in the inferior retina, lens, iris, or optic nerve tissue. With a prevalence of 2-19 per 100,000 live births, coloboma, and microphthalmia, an associated ocular disorder, represent up to 10% of childhood blindness. It manifests due to the failure of choroid fissure closure during eye development, and it is a part of a spectrum of ocular disorders that include microphthalmia and anophthalmia. Use of genetic approaches from classical pedigree analyses to next generation sequencing has identified more than 40 loci that are associated with the causality of ocular coloboma. As we have expanded studies to include singleton cases, hereditability has been very challenging to prove. As such, researchers over the past 20 years, have unraveled the complex interrelationship amongst these 40 genes using vertebrate model organisms. Such research has greatly increased our understanding of eye development. These genes function to regulate initial specification of the eye field, migration of retinal precursors, patterning of the retina, neural crest cell biology, and activity of head mesoderm. This review will discuss the discovery of loci using patient data, their investigations in animal models, and the recent advances stemming from animal models that shed new light in patient diagnosis.

Mitf-family transcription factor function is required within cranial neural crest cells to promote choroid fissure closure

A crucial step in eye development is the closure of the choroid fissure (CF), a transient structure in the ventral optic cup through which vasculature enters the eye and ganglion cell axons exit. Although many factors have been identified that function during CF closure, the molecular and cellular mechanisms mediating this process remain poorly understood. Failure of CF closure results in colobomas. Recently, MITF was shown to be mutated in a subset of individuals with colobomas, but how MITF functions during CF closure is unknown. To address this issue, zebrafish with mutations in mitfa and tfec, two members of the Mitf family of transcription factors, were analyzed and their functions during CF closure determined. mitfa;tfec mutants possess severe colobomas and our data demonstrate that Mitf activity is required within cranial neural crest cells (cNCCs) during CF closure. In the absence of Mitf function, cNCC migration and localization in the optic cup are perturbed. These data shed light on the cellular mechanisms underlying colobomas in individuals with MITF mutations and identify a novel role for Mitf function in cNCCs during CF closure.

Hyaloid vasculature and mmp2 activity play a role during optic fissure fusion in zebrafish

Vertebrate retinal development requires timely and precise fusion of the optic fissure (OF). Failure of this event leads to congenital vision impairment in the form of coloboma. Recent studies have suggested hyaloid vasculature to be involved in OF fusion. In order to examine this link, we analyzed OF fusion and hyaloid vasculogenesis in the zebrafish pax2a noi mutant line. We first determined that pax2a-/- embryos fail to accumulate F-actin in the OF prior to basement membrane (BM) degradation. Furthermore, using 3D and live imaging we observed reduced OF hyaloid vascularization in pax2a-/- embryos. When examining the connection between pax2a loss of function and hyaloid vasculature, we observed significant reduction of talin1 expression, a regulator of hyaloid vasculature. In addition, cranial VEGF expression was found to be reduced in pax2a-/- embryos. Pharmacological inhibition of VEGF signaling phenocopied the pax2a-/- vasculature, F-actin and BM degradation phenotypes. Lastly, we determined that OF associated hyaloid vasculature is a source of mmp2, mmp14a and mmp14b expression and showed that mmp2 is functionally necessary for degradation of OF BM. Taken together we propose a pax2a driven mechanism that ensures proper and timely hyaloid vasculature invasion of the OF in order to facilitate availability of the BM remodeler mmp2.

Impact of Carotid Endarterectomy on Choroidal Thickness and Volume in Enhanced Depth Optical Coherence Tomography Imaging

Purpose

Carotid endarterectomy (CEA) is considered an effective therapeutic method for improving ocular circulation. The choroid is a predominantly vascular tissue; thus, systemic and local vascular alterations may influence its morphology and function. The aim of the current study was to analyse changes in choroidal thickness and volume in patients with significant internal carotid artery stenosis (ICAS) before and after unilateral CEA.

Methods

The 42 eyes of the 21 asymptomatic patients included in the study were divided into two groups: those ipsilateral (EIE) and those contralateral (ECE) to CEA. All participants underwent a complete ophthalmologic examination, including enhanced depth imaging-optical coherence tomography (EDI-OCT). A comparative analysis of subfoveal thickness (CT) and choroidal volume (CV) measured in nine Early Treatment of Diabetic Retinopathy Study (ETDRS) subfields at baseline, on the 2nd day after CEA, and in the 3rd month after CEA was performed.

Results

In the EIE and ECE groups, no significant differences in either CT or CV values before and on the 2nd day after the CEA were observed. In the EIE group, a significant increase in CT and CV in the 3rd month after CEA compared to baseline was noted in the specific ETDRS region. Changes in CT and CV after surgery were positively correlated with the participants' physical activity status and diastolic blood pressure and negatively correlated with the participants' age and smoking status. Additionally, the analysis of changes in CV after CEA showed a positive correlation between the EIE and ECE groups.

Conclusions

CT and CV fluctuations in the central and perifoveal areas visualized with EDI-OCT enabled the observation of the processes of tissue adaptation to variable blood flow conditions.

Genetics of syndromic ocular coloboma: CHARGE and COACH syndromes

Optic fissure closure defects result in uveal coloboma, a potentially blinding condition affecting between 0.5 and 2.6 per 10,000 births that may cause up to 10% of childhood blindness. Uveal coloboma is on a phenotypic continuum with microphthalmia (small eye) and anophthalmia (primordial/no ocular tissue), the so-called MAC spectrum. This review gives a brief overview of the developmental biology behind coloboma and its clinical presentation/spectrum. Special attention will be given to two prominent, syndromic forms of coloboma, namely, CHARGE (Coloboma, Heart defect, Atresia choanae, Retarded growth and development, Genital hypoplasia, and Ear anomalies/deafness) and COACH (Cerebellar vermis hypoplasia, Oligophrenia, Ataxia, Coloboma, and Hepatic fibrosis) syndromes. Approaches employed to identify genes involved in optic fissure closure in animal models and recent advances in live imaging of zebrafish eye development are also discussed.

High-throughput custom capture sequencing identifies novel mutations in coloboma-associated genes: Mutation in DNA-binding domain of retinoic acid receptor beta affects nuclear localization causing ocular coloboma

Uveal coloboma is a potentially blinding congenital ocular malformation caused by the failure of optic fissure closure during the fifth week of human gestation. We performed custom capture high‐throughput screening of 38 known coloboma‐associated genes in 66 families. Suspected causative novel variants were identified in TFAP2A and CHD7, as well as two previously reported variants of uncertain significance in RARB and BMP7. The variant in RARB, unlike previously reported disease mutations in the ligand‐binding domain, was a missense change in the highly conserved DNA‐binding domain predicted to affect the protein's DNA‐binding ability. In vitro studies revealed lower steady‐state protein levels, reduced transcriptional activity, and incomplete nuclear localization of the mutant RARB protein compared with wild‐type. Zebrafish studies showed that human RARB messenger RNA partially reduced the ocular phenotype caused by morpholino knockdown of rarga gene, a zebrafish homolog of human RARB. Our study indicates that sequence alterations in known coloboma genes account for a small percentage of coloboma cases and that mutations in the RARB DNA‐binding domain could result in human disease.

Swept-Source OCT Analysis of the Margin of Choroidal Coloboma: New Insights

PURPOSE

To study the retinal architecture and vitreoretinal interface at the edge of choroidal coloboma using swept-source OCT.

DESIGN

Prospective observational case series at a tertiary eye care center.

PARTICIPANTS

Patients with choroidal coloboma treated at an ophthalmology department and fulfilling the inclusion criteria of the study.

METHODS

Swept-source OCT was carried out in 30 eyes of 20 patients with choroidal coloboma.

MAIN OUTCOME MEASURES

The primary objective was to describe the OCT features at the margin of the coloboma.

RESULTS

Swept-source OCT of the coloboma margin revealed new features in addition to the previously described findings. Two types of transition from normal retina into intercalary membrane (ICM) were noted: abrupt (73.33%) and gradual (26.67%). Outer retinal layers (interdigitation zone and ellipsoid zone) terminated at a variable distance before the retinal pigment epithelium in 56.67% of eyes. Cystic spaces in the ICM (46.67%), schisis-like spitting of the ICM (30%), and breaks in the ICM (6.67%) were seen as well. Subclinical retinal detachment (RD) was also noted in 1 eye. The peculiar features noted at the vitreoretinal interface included vitreous attachment at the coloboma margin (23.33%), vitreous condensation (6.67%), and hill like projections of ICM into the vitreous cavity (26.67%). In the region of the coloboma, sclera and Tenon's capsule could also be analyzed as a hyperreflective lamellar structure and an irregularly arranged less hyperreflective structure.

CONCLUSIONS

Swept-source OCT of the coloboma margin revealed various new features in addition to those described previously. The detection of subclinical RD or early termination of outer retinal layers in selected cases may be helpful in guiding new management protocols.

Regional Gene Expression Profile Comparison Reveals the Unique Transcriptome of the Optic Fissure

Purpose

The optic fissure (OF) is a transient opening in the ventral optic cup (OC) that acts as a passage for blood vessels and retinal ganglion cell axons during early eye development. Failure to close the OF is the developmental basis for uveal coloboma, a congenital blinding eye disease that significantly contributes to childhood blindness. Genes specifically expressed in the OF region may play important roles in OF development and function. The aim of this study was to characterize the transcriptome of OC cells in the OF region and investigate the function of OF-specific genes during OF closure.

Methods

Laser-assisted microdissection was used to collect different regions of OC tissues. Microarray analysis was used to obtain and compare gene expression profiles of different OC regions. RNA in situ hybridization (ISH) was used to further characterize OF-specific gene expression patterns. Morpholino knockdown in zebrafish was used to study the function of a newly discovered OF-specific gene during OF closure.

Results

Microarray comparison revealed that the OC at the OF region exhibited a unique gene expression profile. OC expression patterns of a number of newly discovered OF-specific genes were confirmed by ISH. Morpholino knockdown and downstream target expression and function analysis demonstrated that afap1l2, a newly discovered OF-specific gene, controls OF closure by regulating pax2a expression.

Conclusions

Our study characterized the unique transcriptome of the OF region of the OC and demonstrated the essential role of a newly discovered OF-specific gene in OF closure. This study provides a valuable foundation for future mechanism dissection in OF development and physiology, and for human coloboma etiology exploration.

Temporal characterization of optic fissure basement membrane composition suggests nidogen may be an initial target of remodeling

Fusion of the optic fissure is necessary to complete retinal morphogenesis and ensure proper function of the optic stalk. Failure of this event leads to congenital coloboma, one of the leading causes of pediatric blindness. Mechanistically it is widely accepted that the basement membrane (BM) surrounding the maturing retina needs to be remodeled within the fissure in order to facilitate subsequent epithelial sheet fusion. However, the mechanism driving BM remodeling has yet to be elucidated. As a first step to understanding this critical molecular event we comprehensively characterized the core composition of optic fissure BMs in the zebrafish embryos. Zebrafish optic fissure BMs were found to express laminin a1, a4, b1a, c1 and c3, nidogen 1a, 1b and 2a, collagen IV a1 and a2 as well as perlecan. Furthermore, we observed that laminin, perlecan and collagen IV expression persists in the fissure during fusion, up to 56 hpf, while nidogen expression is downregulated upon initiation of fusion, at 36 hpf. Using immunohistochemistry we also show that nidogen is removed from the BM prior to that of laminin, indicating that remodeling of the BM is an ordered event. Lastly, we characterized retinal morphogenesis in the absence of nidogen function and documented retinal malformation similar to what is observed in laminin mutants. Taken together, we propose a model of BM remodeling where nidogen acts as a linchpin during initiation of optic fissure fusion.

Homozygous frameshift mutations in FAT1 cause a syndrome characterized by colobomatous-microphthalmia, ptosis, nephropathy and syndactyly

A failure in optic fissure fusion during development can lead to blinding malformations of the eye. Here, we report a syndrome characterized by facial dysmorphism, colobomatous microphthalmia, ptosis and syndactyly with or without nephropathy, associated with homozygous frameshift mutations in FAT1. We show that Fat1 knockout mice and zebrafish embryos homozygous for truncating fat1a mutations exhibit completely penetrant coloboma, recapitulating the most consistent developmental defect observed in affected individuals. In human retinal pigment epithelium (RPE) cells, the primary site for the fusion of optic fissure margins, FAT1 is localized at earliest cell-cell junctions, consistent with a role in facilitating optic fissure fusion during vertebrate eye development. Our findings establish FAT1 as a gene with pleiotropic effects in human, in that frameshift mutations cause a severe multi-system disorder whereas recessive missense mutations had been previously associated with isolated glomerulotubular nephropathy.

Loss of the cadherin FAT1 has been associated with nephropathy and epithelial cell adhesion defects. Here, the authors report five families with a syndromic form of coloboma associated with homozygous frameshift variants in FAT1 and recapitulate the phenotype in mutant mice and zebrafish.

Hippo-yap signaling in ocular development and disease

The Hippo-Yes associated protein (Yap) pathway plays an important role in organ size control by regulating cell proliferation, apoptosis, and stem cell renewal. Hippo-Yap signaling also functions at the level of cellular development in a variety of organs through its effects on cell cycle control, cell survival, cell polarity, and cell fate. Because of its important roles in normal development and homeostasis, abnormal regulation of this pathway has been shown to lead to pathological outcomes such as tissue overgrowth, tumor formation, and abnormal organogenesis, including ocular-specific disorders. In this review, we summarize how normal and perturbed control of Yap signaling is implicated in ocular development and disease Developmental Dynamics 247:794-806, 2018. © 2018 Wiley Periodicals, Inc.

Low-vision aids improve the visual performance of children with bilateral chorioretinal coloboma

PURPOSE

To quantify the improvements in visual performance for both distance and near tasks attained by children with bilateral chorioretinal coloboma (CRC) with use of low-vision aids (LVAs).

METHODS

This was a hospital-based, cross-sectional, interventional case series of children with bilateral CRC. Demographic data were collected through a structured questionnaire and review of medical records. Distance and near best-corrected visual acuity, contrast sensitivity, and reading speed were evaluated with refractive correction alone and with the use of LVAs (Keplerian telescopes for distance; handheld magnifiers and a tinted lens [400 nm filter] for near). Effects are presented as medians of differences with 95% binomial-exact confidence intervals.

RESULTS

Six children were included (median age, 11.5 years; range, 7-17 years), of whom 5 were already using LVAs on a daily basis. The use of a Keplerian telescope achieved a significant median improvement in distance best-corrected visual acuity of 0.75 logMAR (95% CI, 0.20-1.20). Contrast sensitivity was also improved across all tested spatial frequencies. Use of near LVAs resulted in a significant median improvement in near reading acuity of 0.47 logRAD (95% CI, 0.28-0.90). Critical print size and reading speed at N10 were also improved.

CONCLUSIONS

LVAs enable meaningful improvements in the visual performance of children with bilateral CRC, allowing noteworthy increases in distance and near visual acuities as well as good reading speeds at small print sizes.

The cellular bases of choroid fissure formation and closure

Defects in choroid fissure (CF) formation and closure lead to coloboma, a major cause of childhood blindness. Despite genetic advances, the cellular defects underlying coloboma remain poorly elucidated due to our limited understanding of normal CF morphogenesis. We address this deficit by conducting high-resolution spatio-temporal analyses of CF formation and closure in the chick, mouse and fish. We show that a small ventral midline invagination initiates CF formation in the medial-proximal optic cup, subsequently extending it dorsally toward the lens, and proximally into the optic stalk. Unlike previously supposed, the optic disc does not form solely as a result of this invagination. Morphogenetic events that alter the shape of the proximal optic cup also direct clusters of outer layer and optic stalk cells to form dorsal optic disc. A cross-species comparison suggests that CF closure can be accomplished by breaking down basement membranes (BM) along the CF margins, and by establishing BM continuity along the dorsal and ventral surfaces of the CF. CF closure is subsequently accomplished via two distinct mechanisms: tissue fusion or the intercalation of various tissues into the inter-CF space. We identify several novel cell behaviors that underlie CF fusion, many of which involve remodeling of the retinal epithelium. In addition to BM disruption, these include NCAD downregulation along the SOX2⁺ retinal CF margin, and the protrusion or movement of partially polarized retinal cells into the inter-CF space to mediate fusion. Proximally, the inter-CF space does not fuse or narrow and is instead loosely packed with migrating SOX2⁺/PAX2⁺/Vimentin⁺ astrocytes until it is closed by the outgoing optic nerve. Taken together, our results highlight distinct proximal-distal differences in CF morphogenesis and closure and establish detailed cellular models that can be utilized for understanding the genetic bases of coloboma.

Morphogenetic defects underlie Superior Coloboma, a newly identified closure disorder of the dorsal eye

The eye primordium arises as a lateral outgrowth of the forebrain, with a transient fissure on the inferior side of the optic cup providing an entry point for developing blood vessels. Incomplete closure of the inferior ocular fissure results in coloboma, a disease characterized by gaps in the inferior eye and recognized as a significant cause of pediatric blindness. Here, we identify eight patients with defects in tissues of the superior eye, a congenital disorder that we term superior coloboma. The embryonic origin of superior coloboma could not be explained by conventional models of eye development, leading us to reanalyze morphogenesis of the dorsal eye. Our studies revealed the presence of the superior ocular sulcus (SOS), a transient division of the dorsal eye conserved across fish, chick, and mouse. Exome sequencing of superior coloboma patients identified rare variants in a Bone Morphogenetic Protein (Bmp) receptor (BMPR1A) and T-box transcription factor (TBX2). Consistent with this, we find sulcus closure defects in zebrafish lacking Bmp signaling or Tbx2b. In addition, loss of dorsal ocular Bmp is rescued by concomitant suppression of the ventral-specific Hedgehog pathway, arguing that sulcus closure is dependent on dorsal-ventral eye patterning cues. The superior ocular sulcus acts as a conduit for blood vessels, with altered sulcus closure resulting in inappropriate connections between the hyaloid and superficial vascular systems. Together, our findings explain the existence of superior coloboma, a congenital ocular anomaly resulting from aberrant morphogenesis of a developmental structure.

Ocular coloboma is a disease characterized by gaps in the lower portion of the eye and can affect the iris, lens, or retina, and cause loss of vision. Coloboma arises from incomplete closure of a transient fissure on the underside of the developing eye. Therefore, our identification of patients with similar tissue defects, but restricted to the superior half of eye, was surprising. Here, we describe an ocular developmental structure, the superior ocular sulcus, as a potential origin for the congenital disorder superior coloboma. Formation and closure of the sulcus are directed by dorsal-ventral eye patterning, and altered patterning interferes with the role of the sulcus as a pathway for blood vessel growth onto the eye.

Goldenhar syndrome: current perspectives

BACKGROUND

Progress in medical branches that has taken place since the first child with Goldenhare syndrome (GS) had been described in 1952 by Maurice Goldenhar, facilitated better understanding of this congenital defect. It also gave new perspectives and the opportunity to achieve satisfactory treatment results, mainly due to development of surgical techniques.

DATA SOURCES

Based on the literature and own experience, we discussed the phenotype of presentation of GS, ethiopathogenesis, genetic counselling and treatment with particular emphasis on surgery correction of hemifacial microsomia.

RESULTS

The spectrum of GS abnormalities ranges from mild to severe ones and include patients with barely noticeable facial asymmetry to very pronounced facial defect with more or less severe abnormalities of internal organs and/or skeleton. It is characterized most commonly by impaired development of eyes, ears, lips, tongue, palate, mandible, maxilla, zygomatic and orbital structures and deformations of the teeth structures. Ethiopathogenesis is multifactorial and dependent on genetic and environmental factors but there are still many unknowns about the syndrome which should be revealed.

CONCLUSIONS

Patients with GS due to a large variety of abnormalities and different severity of symptoms pose a challenge for clinicians. All of this necessitate an individual approach to each single patient and involvement a team of specialists in treatment planning. It is a complex, long-lasting, multidisciplinary process and should be divided into stages, according to patient's age, as well as the extent and severity of observed abnormalities. Neonatologists and pediatricians are involved in care of these patients from the onset.

The Transcription Factor Foxg1 Promotes Optic Fissure Closure in the Mouse by Suppressing Wnt8b in the Nasal Optic Stalk

During vertebrate eye morphogenesis, a transient fissure forms at its inferior part, known as the optic fissure. This will gradually close, giving rise to a healthy, spherical optic cup. Failure of the optic fissure to close gives rise to an ocular disorder known as coloboma. During this developmental process, Foxg1 is expressed in the optic neuroepithelium, with highest levels of expression in the nasal optic stalk. Foxg1-/- mutant mice have microphthalmic eyes with a large ventral coloboma. We found Wnt8b expression upregulated in the Foxg1-/- optic stalk and hypothesized that, similar to what is observed in telencephalic development, Foxg1 directs development of the optic neuroepithelium through transcriptional suppression of Wnt8b To test this, we generated Foxg1-/-;Wnt8b-/- double mutants of either sex and found that the morphology of the optic cup and stalk and the closure of the optic fissure were substantially rescued in these embryos. This rescue correlates with restored Pax2 expression in the anterior tip of the optic fissure. In addition, although we do not find evidence implicating altered proliferation in the rescue, we observe a significant increase in apoptotic cell density in Foxg1-/-;Wnt8b-/- double mutants compared with the Foxg1-/- single mutant. Upregulation of Wnt/β-catenin target molecules in the optic cup and stalk may underlie the molecular and morphological defects in the Foxg1-/- mutant. Our results show that proper optic fissure closure relies on Wnt8b suppression by Foxg1 in the nasal optic stalk to maintain balanced apoptosis and Pax2 expression in the nasal and temporal edges of the fissure.SIGNIFICANCE STATEMENT Coloboma is an ocular disorder that may result in a loss of visual acuity and accounts for ∼10% of childhood blindness. It results from errors in the sealing of the optic fissure (OF), a transient structure at the bottom of the eye. Here, we investigate the colobomatous phenotype of the Foxg1-/- mutant mouse. We identify upregulated expression of Wnt8b in the optic stalk of Foxg1-/- mutants before OF closure initiates. Foxg1-/-;Wnt8b-/- double mutants show a substantial rescue of the Foxg1-/- coloboma phenotype, which correlates with a rescue in molecular and cellular defects of Foxg1-/- mutants. Our results unravel a new role of Foxg1 in promoting OF closure providing additional knowledge about the molecules and cellular mechanisms underlying coloboma formation.

Association of Pediatric Choroidal Neovascular Membranes at the Temporal Edge of Optic Nerve and Retinochoroidal Coloboma

PURPOSE

To describe the characteristics of pediatric choroidal neovascular membranes (CNVs) associated with retinochoroidal and optic nerve coloboma using optical coherence tomography (OCT) and their response to treatment.

DESIGN

Retrospective case series.

METHODS

Retrospective review of children <16 years of age with CNV and retinochoroidal and optic nerve coloboma from 1995-2015 who underwent OCT imaging using either handheld (Bioptigen, Morrisville, NC) or tabletop OCT (Spectralis; Heidelberg, Carlsbad, CA).

RESULTS

Eight eyes of 8 patients (3 males, 5 females) with a mean age of 4.1 ± 3.9 years (range 6 months-10 years) at diagnosis were included. Mean follow-up was 21.4 ± 12.1 months (range 7-38 months). An optic nerve coloboma was present in 2 eyes and combined optic nerve and retinochoroidal coloboma in 6 eyes. In all eyes, CNVs were located at the temporal margin of the coloboma closest to the macula. Fluorescein angiogram characteristics included staining without leakage suggesting inactivity (n = 6) and leakage (n = 2). OCT characteristics included subretinal fluid (n = 5), intraretinal fluid and cysts (n = 1), and subretinal hyperreflective material (n = 7). Two eyes received intravitreal bevacizumab (range 3-6) injections, one of which also underwent focal peripapillary laser. Both eyes showed improvement in subretinal or intraretinal fluid on OCT. Vision at presentation among those quantified ranged from 20/200 to 20/40 and at final follow-up from 20/400 to 20/30. Genetic or systemic abnormalities were seen in 6 patients.

CONCLUSIONS

Association of pediatric CNV occurrence at the temporal margin of retinochoroidal and optic nerve colobomas closest to the fovea has not been established before and careful OCT and angiographic assessment of this region is warranted. The CNV lesions exhibit a varied degree of response to treatment.

The hyaloid vasculature facilitates basement membrane breakdown during choroid fissure closure in the zebrafish eye

A critical aspect of vertebrate eye development is closure of the choroid fissure (CF). Defects in CF closure result in colobomas, which are a significant cause of childhood blindness worldwide. Despite the growing number of mutated loci associated with colobomas, we have a limited understanding of the cell biological underpinnings of CF closure. Here, we utilize the zebrafish embryo to identify key phases of CF closure and regulators of the process. Utilizing Laminin-111 as a marker for the basement membrane (BM) lining the CF, we determine the spatial and temporal patterns of BM breakdown in the CF, a prerequisite for CF closure. Similarly, utilizing a combination of in vivo time-lapse imaging, β-catenin immunohistochemistry and F-actin staining, we determine that tissue fusion, which serves to close the fissure, follows BM breakdown closely. Periocular mesenchyme (POM)-derived endothelial cells, which migrate through the CF to give rise to the hyaloid vasculature, possess distinct actin foci that correlate with regions of BM breakdown. Disruption of talin1, which encodes a regulator of the actin cytoskeleton, results in colobomas and these correlate with structural defects in the hyaloid vasculature and defects in BM breakdown. cloche mutants, which entirely lack a hyaloid vasculature, also possess defects in BM breakdown in the CF. Taken together, these data support a model in which the hyaloid vasculature and/or the POM-derived endothelial cells that give rise to the hyaloid vasculature contribute to BM breakdown during CF closure.

Engineering a Light-Attenuating Artificial Iris

Purpose

Discomfort from light exposure leads to photophobia, glare, and poor vision in patients with congenital or trauma-induced iris damage. Commercial artificial iris lenses are static in nature to provide aesthetics without restoring the natural iris's dynamic response to light. A new photo-responsive artificial iris was therefore developed using a photochromic material with self-adaptive light transmission properties and encased in a transparent biocompatible polymer matrix.

Methods

The implantable artificial iris was designed and engineered using Photopia, a class of photo-responsive materials (termed naphthopyrans) embedded in polyethylene. Photopia was reshaped into annular disks that were spin-coated with polydimethylsiloxane (PDMS) to form our artificial iris lens of controlled thickness.

Results

Activated by UV and blue light in approximately 5 seconds with complete reversal in less than 1 minute, the artificial iris demonstrates graded attenuation of up to 40% of visible and 60% of UV light. There optical characteristics are suitable to reversibly regulate the incident light intensity. In vitro cell culture experiments showed up to 60% cell death within 10 days of exposure to Photopia, but no significant cell death observed when cultured with the artificial iris with protective encapsulation. Nuclear magnetic resonance spectroscopy confirmed these results as there was no apparent leakage of potentially toxic photochromic material from the ophthalmic device.

Conclusions

Our artificial iris lens mimics the functionality of the natural iris by attenuating light intensity entering the eye with its rapid reversible change in opacity and thus potentially providing an improved treatment option for patients with iris damage.

A 3-Day-Old Girl Referred From Her Pediatrician for Oral Ulcerations

A 3-day-old girl was referred from her pediatrician for oral ulcerations. The patient was otherwise well appearing and afebrile. Her prenatal and antenatal courses were unremarkable, except for a failed routine hearing screen. The patient's examination was notable for several yellowish ulcers on erythematous bases located on her anterior tonsillar pillars. The patient also had a right coloboma and a II/VI systolic ejection murmur. Laboratory analyses revealed a traumatic lumbar puncture with 182 000 red blood cells and 808 white blood cells, as well as a complete blood count that showed thrombocytopenia and leukocytosis. During the patient's hospitalization, she developed a new facial rash. Her physical examination findings, along with her diagnostic evaluation and hospital course, ultimately led to 2 surprising diagnoses elaborated on in this case discussion.