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Comparative Anatomy and Physiology of the Mammalian Eye
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
Embryologically, the vitreous is developed in three stages. The primary vitreous fills the space between the invaginating optic cup and the lens placode. It is, in turn, filled by vascularized mesoderm which extends from the optic nerve to the posterior lens and connects with the tunica vasculosa lentis (Figure 16). The secondary vitreous forms around the primary and is secreted by the neuroectoderm. The primary vitreous will eventually degenerate leaving its remnant, Cloquet’s canal, and the secondary vitreous to fill the posterior cavity of the eye. Failure of this atrophy results in a persistent hyaloid artery and possibly an associated cataract. Although the primary vitreous atrophies in all mammals, it does not do so at the same time. In humans, the primary vitreous does not carry blood beyond the seventh month,120 while in the dog and rat, these vessels can remain patent for up to 17 days postpartum.122,123 In addition, it has been estimated that 60% of Sprague-Dawley and 90% of Ola:Wistar rats at 6 weeks of age have a persistence of the hyaloid vessels which may be associated with vitreal hemorrhage.123 The tertiary vitreous is the lenticular zonules.
Anterior vitrectomy
Published in A Peyman MD Gholam, A Meffert MD Stephen, D Conway MD FACS Mandi, Chiasson Trisha, Vitreoretinal Surgical Techniques, 2019
In this rare condition, also termed persistent fetal vasculature,33 the goals of surgery are to restore a visual pathway and relieve all traction on the ciliary processes. This is achieved by first performing a pars plicata lensectomy, followed by removal of the retrolental fibrovascular membrane. Finally, the hyaloid artery is incised and cauterized. Because this surgery is usually performed in infants within the first few months of life and the eyes are usually microphthalmic, an anterior limbal approach has been advocated.15 However, unless echography demonstrates a retinal detachment, the pars plicata approach is generally favored. The 23- and 25-gauge vitrectomy instruments are preferred in infants to reduce the risk of retinal dialysis and retinal detachment. Because an intraocular lens (IOL) is not recommended in these cases, a total lensectomy is performed.
Write short notes on the prenatal development of the lens. Use annotated diagrams where possible
Published in Nathaniel Knox Cartwright, Petros Carvounis, Short Answer Questions for the MRCOphth Part 1, 2018
Nathaniel Knox Cartwright, Petros Carvounis
The hyaloid artery gives rise to a series of small capillaries that anastomose with choroidal and long ciliary arteries to form a vascular capsule, the tunica vasculosa lentis, providing the rich nutrient supply necessary for the rapid growth of the lens during development. This capsule regresses shortly before birth.
Hyalocyte functions and immunology
Published in Expert Review of Ophthalmology, 2022
Stefaniya K Boneva, Julian Wolf, Peter Wieghofer, J Sebag, Clemens AK Lange
Around the fourth week of gestation during development of the eye, mesodermal cells enter the forming eye cup via the optic fissure, and, together with surrounding fibroblasts, constitute the primordial vitreous. Some of the mesodermal cells exhibit the morphological features of cells destined to be hyalocytes, expressing myeloid cell markers, such as major histocompatibility complex (MHC) and cluster of differentiation 45 (CD45) antigens, and can therefore be considered hyalocyte precursor cells [10,11]. The mesodermal cells further contribute to the anlage of the hyaloid vascular system, which is composed of the vasa hyaloidea propria, tunica vasculosa lentis, the pupillary membrane, and the hyaloid artery (Figure 2). The vasa hyaloidea propria anastomoses with the tunica vasculosa lentis and pupillary membrane to nourish the developing anterior segment. After reaching its zenith at approximately the 10th week of gestation, regression of the hyaloid vasculature is observed [12]. This process is vital for a clear optical axis and failure can result in crucial impairment of vitreo-retinal and ocular development. Changes in the proteomic profile of vitreous from human embryos aged 14 to 20 weeks gestation have suggested cytokine events that may be important in hyaloid vasculature regression [13].
Genetic disease is a common cause of bilateral childhood cataract in Denmark
Published in Ophthalmic Genetics, 2021
Line Kessel, Daniella Bach-Holm, Moug Al-Bakri, Laura Roos, Allan Lund, Karen Grønskov
Congenital and childhood cataracts are rare but globally the most important cause of treatable childhood blindness (1). The pooled prevalence of congenital cataract across studies is 4.24 per 10,000 (2). Childhood cataracts can be caused by a wide range of etiologies. Unilateral cataracts are often associated with eye malformations such as a persistent hyaloid artery and/or microphthalmia whereas bilateral cataracts are more often associated with genetic diseases including syndromes (3). Because of lack of systemic associations in unilateral cataract, it is generally agreed that these children do not require further work up (4). There is no general agreement to which extent systemic work up is necessary in children with bilateral cataracts. The American Association of Ophthalmology do not recommend systemic and laboratory evaluations in children with a family history and no other medical problems. In children without a family history, they recommend to perform a urine metabolic evaluation, to test for congenital infections and to do blood tests for calcium, phosphorus, glucose and galactokinase (5). Others suggest to include next generation sequencing (NGS) as first-line work-up for children with bilateral cataracts without a family history as it may dramatically alter the subsequent management of the children and families (6). A retrospective chart review found that a specific diagnosis could be made in 10/15 children using a NGS panel specific for cataract-related genes (7).
Further delineation of the oculoauricular syndrome phenotype: A new family with a novel truncating HMX1 mutation
Published in Ophthalmic Genetics, 2018
Ghada M.H. Abdel-Salam, Mohamed S. Abdel-Hamid, Mennat I. Mehrez, Ahmad M. Kamal, Mohamed B. Taher, Hanan H. Afifi
Ophthalmological examination revealed bilateral microcornea (8 mm horizontal diameter), iris coloboma, aphakia, microphthalmia (axial lengths measured ± 19.8mm in the right and 17.9 mm in the left). The right fundus showed optic disc coloboma while the left showed remnants of posterior hyaloid artery (Figure 3). Electroretinogram (scotopic and photopic) of both eyes showed moderately reduced response indicating moderate retinal dysfunction up to the ganglion cell layers. It also showed moderately reduced photopic flicker responses in both eyes. Flash VEP and pattern VEP detected moderately impaired retinocortical transmission. Both eyes were equally involved.