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Free Content The Current Embryology of the Orbit

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The eye is truly an extension of the brain and the end organ of the visual pathway. An understanding of how the eye develops and then how the extraocular structures arise allows not only a better understanding of their anatomy but also provides insight into the congenital problems that may arise. The development of the orbit is the result of complex multifactorial molecular pathways that are just beginning to be better understood, and this understanding is primarily based on animal models. This review takes the reader step by step through this embryology, with numerous figures to help the reader better understand the text. A section is also included that mentions some of the more common gene-related orbital abnormalities.

Learning Objective: The reader will understand the embryology of the orbit and how this relates to the developmental variations that occur.

Keywords: AIPL1 = aryl hydrocarbon receptor interacting protein-like 1; AMD = age-related macular degeneration; ANG = angiopoietin; BF = boron fluoride, a triggering protein of the alternative pathway of complement activation; BMP = bone morphogenic protein; CHORDIN = a bone morphogenetic protein antagonist; CHST = carbohydrate sulfotransferase 6 enzyme; CHX = paired-type homeodomain protein; CNG = cone cell cyclic nucleotide-gated ion channel; CRB = Crumbs family member 1 for photoreceptor morphogenesis; CRX = cone-rod homeobox gene; CRYAB = alpha-crystallin B chain protein CRX; CX = lens specific connexins; CYP1B1 = cytochrome P450 Family 1 Subfamily B Member 1 the CYP1B1 gene provides instructions for the cytochrome P450 superfamily of enzymes; CYP4V2 = the CYP4V2 gene provides instructions for the cytochrome P450 superfamily of enzymes; D1S = a short tandem repeat marker; DAN = deadenylating nuclease, a negative regulator of Nodal signaling; EFTF = eye field transcription factor; EGFR = signaling pathway; ET = endothelin, a secreted signaling peptide; EYA= eyes absent homolog, a transcription factor; FERM = domain is a widespread protein module involved in localizing proteins to the plasma membrane; FGF = fibroblastic growth factor; FOX = forkhead box transcription factor; FOXE3 = forkhead box E3 gene this is a part of the FOX gene family; FRMD = FERM domain-containing protein; GATA30F04 = a complement regulatory gene locus which can predispose people to degenerative myopia; GCD = granular dystrophy; GH = glycoside hydrolase, a family of proteins; GUCY2D = guanylate cyclase 2D, a membrane (retina) specific gene; HES = hairy and enhancer of split-1 bHLH transcription factor suppressor; HESX = mutations in this homeobox gene Hesx1 are associated with septo-optic dysplasia in humans; HF1 = a gene factor which encodes a major inhibitor of the alternative complement pathway, and it is associated with the risk for age-related macular degeneration; HSF = heat shock transcription factor; KRT = KRT family of genes provide instructions for making proteins keratins; LCA = Leber congenital amaurosis; LCD = lattice dystrophy; LHX = a homeobox gene that functions as a transcriptional regulator; LIM = lens intrinsic membrane protein; LMX1B = LIM homeobox transcription factor 1β; MAF = transcription factor Maf also known as proto-oncogene c-Maf; MIP = major intrinsic protein encodes lens fiber major intrinsic protein; MIS1 = gene encodes mitochondrial C (1)-tetrahydrofolate synthase; MITF = microphthalmia-associated transcription factor; MT-ND = mitochondrial DNA mutation site; ND = Norrie disease; NDP = Norrie disease pseudogliomas gene; NOGGIN = a BMP antagonist involved in many forms of embryonic development; NOTCH = a transmembrane receptor for Delta and Serrate, mediating cell‐cell interactions; NYS = nystagmus; NYS1 = nystagmus 1 gene encodes for X-linked idiopathic congenital nystagmus; OTX = a homeobox protein; PAX = paired box protein; PHPV = persistent hyperplastic primary vitreous; PIP5K3 = Arabidopsis thaliana gene encodes PIP5K3 1-phosphatidylinositol-4-phosphate 5-kinase; PITX3 = pituitary homeobox 3 transcription factor; PROX1 = prospero-related homeobox-1; RA = retinoic acid; RALDH = retinal dehydrogenase gene; RAX = retina and anterior neural fold homeobox gene; ROP = retinopathy of prematurity; RPE = retinal pigment epithelium-specific protein; RPE65 = retinal pigment epithelium-specific protein 65kDa; RPGRIP1 = ribosomal protein gene; RX = retinal and anterior neural fold homeobox gene; SHH = sonic hedgehog; SIX = the Six family genes function as transcription factors; SOH = cysteine sulfenic acid functions in redox regulation; SOX = Sry-related homeobox gene; STS = sequence-tagged site; TBX = T-box protein, a transcription factor; TGF = transforming growth factor; TGFBI = transforming growth factor β induced; TLL = tubulin tyrosine ligase; TULPL = a member of the tubby gene family; VAX = homeodomain proteins that control neuroepithelial segregation; VEGF = vascular endothelial growth factor; WNT = Wingless family of secreted signaling molecules; XL-FEVR = X-linked familial exudative vitreoretinopathy; decorin = a proteoglycan; fibrillin = a large protein that is transported outside the cell and forms the microfilaments of the extracellular matrix; follistatin = also known as activin-binding protein, functions in the binding and bioneutralization of members of the transforming growth factor β superfamily; gelsolin = actin-binding protein that is a key regulator of actin filament assembly and disassembly; mtDNA = mitochondrial DNA

Document Type: Research Article

Publication date: July 1, 2017

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