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Eye (London, England) Aug 2021Typical ocular coloboma is caused by defective closure of the embryonal fissure. The occurrence of coloboma can be sporadic, hereditary (known or unknown gene defects)... (Review)
Review
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.
Topics: Coloboma; Humans; Microphthalmos; Optic Disk; Retinal Detachment; Visual Acuity
PubMed: 33746210
DOI: 10.1038/s41433-021-01501-5 -
Progress in Retinal and Eye Research Nov 2022The development of the vertebrate eyes is a complex process starting from anterior-posterior and dorso-ventral patterning of the anterior neural tube, resulting in the... (Review)
Review
The development of the vertebrate eyes is a complex process starting from anterior-posterior and dorso-ventral patterning of the anterior neural tube, resulting in the formation of the eye field. Symmetrical separation of the eye field at the anterior neural plate is followed by two symmetrical evaginations to generate a pair of optic vesicles. Next, reciprocal invagination of the optic vesicles with surface ectoderm-derived lens placodes generates double-layered optic cups. The inner and outer layers of the optic cups develop into the neural retina and retinal pigment epithelium (RPE), respectively. In vitro produced retinal tissues, called retinal organoids, are formed from human pluripotent stem cells, mimicking major steps of retinal differentiation in vivo. This review article summarizes recent progress in our understanding of early eye development, focusing on the formation the eye field, optic vesicles, and early optic cups. Recent single-cell transcriptomic studies are integrated with classical in vivo genetic and functional studies to uncover a range of cellular mechanisms underlying early eye development. The functions of signal transduction pathways and lineage-specific DNA-binding transcription factors are dissected to explain cell-specific regulatory mechanisms underlying cell fate determination during early eye development. The functions of homeodomain (HD) transcription factors Otx2, Pax6, Lhx2, Six3 and Six6, which are required for early eye development, are discussed in detail. Comprehensive understanding of the mechanisms of early eye development provides insight into the molecular and cellular basis of developmental ocular anomalies, such as optic cup coloboma. Lastly, modeling human development and inherited retinal diseases using stem cell-derived retinal organoids generates opportunities to discover novel therapies for retinal diseases.
Topics: Humans; Transcription Factors; Gene Expression Regulation, Developmental; Cell Differentiation; Eye; Retina; Signal Transduction; Retinal Diseases
PubMed: 35817658
DOI: 10.1016/j.preteyeres.2022.101093 -
Taiwan Journal of Ophthalmology 2023The crystalline lens is an important structure in the eye that starts to develop as early as the 22 day of gestation, with further differentiation that continues after... (Review)
Review
The crystalline lens is an important structure in the eye that starts to develop as early as the 22 day of gestation, with further differentiation that continues after the induction. Congenital anomalies of the lens may involve the size, shape, and position of the lens. They may sometimes be associated with anterior segment dysgenesis or persistence of the tunica vasculosa lentis and hyperplastic vitreous and hyaloid system. Manifestations of anomalies of the lens shape are usually seen in early or late childhood however may sometimes be delayed into adulthood based on the level of visual impairment or the presence or absence of any syndromic associations. While lens coloboma has more often been reported in isolation, the more commonly implicated genes include the PAX6 gene, lenticonus in particular anterior is often part of Alport syndrome with extra-ocular manifestations in the kidneys and hearing abnormalities due to mutations in the alpha 5 chain of the Type IV collagen gene. Recognition of these manifestations and obtaining a genetic diagnosis is an important step in the management. The level of visual impairment and amblyopia dictates the outcomes in patients managed either conservatively with optical correction as well as surgically where deemed necessary. This review discusses the various anomalies of the lens shape with its related genetics and the management involved in these conditions.
PubMed: 38249493
DOI: 10.4103/tjo.TJO-D-23-00076 -
Oman Journal of Ophthalmology 2023Marfan's syndrome (MFS) is an autosomal dominant connective tissue disorder with defect in the fibrillin-1 gene. The most common ocular manifestation is subluxated lens...
Marfan's syndrome (MFS) is an autosomal dominant connective tissue disorder with defect in the fibrillin-1 gene. The most common ocular manifestation is subluxated lens in the superotemporal direction, accounting for 50%-85% of total cases. The association of lens coloboma with MFS has been described in literature, but the coexistence of lens coloboma with ectopia lentis is a rare feature. Here, we describe three cases of MFS including a case of bilateral lens coloboma with ectopia lentis: case 1 - a 39-year-old male with inferotemporal lens subluxation in the right eye and superotemporal lens subluxation in the left eye with open-angle glaucoma and high myopia, case 2 - a 15-year-old child with bilateral superonasal lens subluxation with lens coloboma, and case 3 - a 56-year-old female with bilateral lens coloboma. Case 1 and case 2 had clear lenses with good refractive correction; hence, they were optically rehabilitated with contact lenses, whereas case 3 was advised for cataract surgery. It is important to distinguish the lens coloboma from a more common entity, ectopia lentis as former usually remains stable while the latter might need a surgical intervention.
PubMed: 37602182
DOI: 10.4103/ojo.ojo_108_22