Molecular Anatomy of the Vertebrate Eye
Marcel E. Nimni in Collagen, 1988
The wall of the eye consists of three layers. The outermost layer is composed of opaque sclera and transparent cornea which provide a slightly elastic envelope that maintains the shape of the eye. The middle vascular layer is made up of the choroid, ciliary body, and iris. The innermost layer is the light-sensitive retina (Figure 1). The cornea is composed primarily of extracellular matrices and is covered on its anterior and posterior surfaces by a sheet of cells. The multilayered epithelium and a single-layered endothelium are apposed to their associated basement membranes. The anterior chamber is bounded by the cornea anteriorly and the iris posteriorly. The lens lies behind the iris and within the anterior and posterior capsule, and is attached to the muscle of the ciliary body by the fine fibers of the zonules of Zinn. The vitreous is the transparent gelatinous mass that fills the eye behind the lens. The retina is formed of light-sensitive nerve cells that transmit the visual impulses to the brain via the optic nerve.
Management of endophthalmitis
A Peyman MD Gholam, A Meffert MD Stephen, D Conway MD FACS Mandi, Chiasson Trisha in Vitreoretinal Surgical Techniques, 2019
Early diagnosis and appropriate treatment with intraocular antibiotics are important factors in the successful management of endophthalmitis. Emerging resistance of organisms to standard antibiotic therapy has forced clinicians to continually evaluate the best intraocular antibiotics for the treatment of endophthalmitis. Although drug combinations are necessary to cover the full range of bacteria causing endophthalmitis, antimicrobial synergy is probably less important in endophthalmitis treatment, because of the high intravitreal concentrations of individual antibiotics achieved by intravitreal injection. Acute postoperative endophthalmitis is treated by a combination of broad-spectrum antibiotics (either vancomycin or clindamycin, with either amikacin or ceftazidime), which are administered intravitreally, subconjunctivally, or topically. In vitrectomized eyes, the dose of antibiotic must be reduced to one-quarter of the nonvitrectomized dose (Table 52.5).80 This is recommended because antibiotic toxicity has been evaluated most often in the nonvitrectomized eye, where the vitreous prevents rapid diffusion of antibiotics toward the retina. The vitreous reduces the concentration of antibiotic that reaches the retina, while allowing the antibiotic to be cleared through the anterior chamber. The recommended doses of common antibiotics are shown in Table 52.5.
Tumors of the Nervous System
Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw in Hankey's Clinical Neurology, 2020
Visual loss: Because of enlargement of retinal hemangioblastoma.Exudative retinopathy/macular edema.Retinal detachment.Vitreous hemorrhage.Retinal lesions are often in the periphery of the retina, but large draining veins may be seen at the disc.
The Roles of Vitreous Biomechanics in Ocular Disease, Biomolecule Transport, and Pharmacokinetics
Published in Current Eye Research, 2023
Richard H. Luo, Nguyen K. Tram, Ankur M. Parekh, Raima Puri, Matthew A. Reilly, Katelyn E. Swindle-Reilly
The vitreous humor is a gel-like, soft, and transparent ocular tissue located between the lens and the retina, occupying 80% of the eye’s volume.1 The vitreous contains very few cells, mostly phagocytes, which remove unwanted cellular debris in the visual field, and hyalocytes, which turn over hyaluronic acid. However, the vitreous humor is also surrounded by many different types of cells, including fibroblasts, astrocytes, macrophages, white blood cells, lens epithelial cells, retinal pigment epithelial cells, and ciliary epithelial cells.2 Other noncellular components of the vitreous include water (98–99%) and a framework of collagen fibers and hyaluronic acid. The hyaluronic acid coils are interspersed in a network of collagen type II which is loosely crosslinked with collagen type IX bridges.3 The viscoelasticity of the vitreous is maintained by a balance between collagen, which provides elasticity, and hyaluronic acid, which provides viscosity, to the vitreous.
Vitreous Humor: Composition, Characteristics and Implication on Intravitreal Drug Delivery
Published in Current Eye Research, 2023
Deepakkumar Mishra, Shilpkala Gade, Katie Glover, Ravi Sheshala, Thakur Raghu Raj Singh
Occupying the vitreous cavity, the vitreous humour is a homogenous, viscoelastic hydrogel structure that helps to maintain the shape of the eyeball through its continuous contact with the retina by inner limiting membrane (Figure 1(A)). The vitreous also acts to prevent physical damage to lens and retina by absorbing any mechanical impact, as well as preventing oxidative damage.20,21 Another crucial role of the vitreous is in the transmission of light, as the transparent nature of the vitreous allows the passage of refracted light towards the photoreceptors of the retinal tissue. The received light is then converted to electrical signals by the photoreceptors which are subsequently processed in the brain. Similar the cornea, the vitreous has a refractive index of 1.336,22,23 which is crucial to its role in the transmission of light.
Review of Vitreopapillary Traction Syndrome
Published in Neuro-Ophthalmology, 2020
Rami S. Gabriel, Chantal J. Boisvert, Mitul C. Mehta
New research has been ongoing in developing pharmaceutical agents that cause liquefication of the vitreous. Ocriplasmin (formerly microplasmin) is a recombinant form of human plasmin that contains proteolytic activity on proteins anchoring the vitreoretinal interface as well as lacking activity against type IV collagen-an essential component of the inner limiting membrane. This allows for targeted activity in the vitreous while minimising toxic effects to the retina.19 Trials have been conducted using this agent for VMT including two large randomised controlled phase 3 trials. Comparison of ocriplasmin injection to saline (placebo) has shown resolution of vitreomacular adhesion in 26.5% of eyes compared to 10.1%, respectively. Though these results are promising, many retinal specialists have abandoned the use of ocriplasmin due to its toxicity. Furthermore, its use in VPT would be limited due to the histopathological differences between VMT and VPT.
Related Knowledge Centers
- Collagen
- Cornea
- Eye
- Posterior Vitreous Detachment
- Retina
- Vitreous Chamber
- Gel
- Lens
- Aqueous Humour
- Vitreous Membrane