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An Asian woman with blurred vision
Published in Tim French, Terry Wardle, The Problem-Based Learning Workbook, 2022
Cataracts remain the most common cause of blindness worldwide and the most common cause of visual loss in the elderly. The problem lies within the lens; the anatomy is shown in Figure 19.2. The lens is an isolated structure constructed of specialised epithelial cells encased in an elastic capsule. The majority of the lens consists of lens fibres (elongated lens epithelial cells that have lost their nuclei and many of their organelles). Between the capsule and the outermost layer of lens fibres is a single layer of epithelial cells. These metabolically active lens cells divide, to create new lens fibres. The oldest lens fibres remain in the centre of the lens forming the ‘nucleus’ of the lens. New lens fibres are laid down around this ‘nucleus’. The lens capsule is an elastic basement membrane secreted by the lens epithelial cells that surround the cells of the lens.
The Special Sense Organs and Their Disorders
Published in Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss, Understanding Medical Terms, 2020
Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss
Treatment for cataracts varies from frequent changes in eyeglasses to compensate for gradual vision loss, to surgery in which the lens is removed and replaced with an artificial lens. Removal of the entire lens is termed an intracapsular extraction, while extracapsular extraction denotes retention of the posterior portion of the lens capsule. Phacoemulsification is a technique utilizing ultrasonic vibration to disintegrate the lens for aspiration. A combination of the artificial lens and bifocal glasses or contact lenses is used to restore focusing ability. Refractive errors and unilateral aphakia (absence of the crystalline lens) can also be treated with corneal contact leases.
The nervous system and the eye
Published in C. Simon Herrington, Muir's Textbook of Pathology, 2020
James A.R. Nicoll, William Stewart, Fiona Roberts
The biconvex lens substance is formed by cells that contain transparent crystalline lens proteins. A cataract is any opacity of the crystalline lens. The cells of the lens are enclosed in an elastic membrane, the lens capsule. Metabolism of the lens is maintained by diffusion of nutrients from the aqueous. Any change in the biochemical composition of the aqueous fluid, as occurs in metabolic diseases, e.g. diabetes mellitus or hypocalcaemia, may result in the formation of abnormal opaque proteins in the damaged lens cells. Other insults such as uveitis, ionizing radiation, or trauma may also result in opacities. Congenital cataracts may form if there is damage to the developing lens fibres in utero, e.g. as a result of rubella infection. The most common form of cataract, however, is senile cataract, which is due to the degradation of lens proteins in the oldest, central part of the lens. Most cases of cataract are treated by removal of the opaque lens matter by ‘phakoemulsification’ and the insertion of a plastic lens implant into the residue of the lens capsule behind the iris.
A Review of Lens Biomechanical Contributions to Presbyopia
Published in Current Eye Research, 2023
The lens capsule is a very thick (∼10 µm in the human eye) basement membrane with very low rates of protein turnover.52 We are not aware of any studies which have elucidated whether or by which mechanism the capsule is remodeled, though certainly any remodeling would necessarily be performed by the LECs. Lens capsule production is thought to occur only in the anterior capsule as LECs secrete capsule proteins in areas of high proliferation.3,44,61 It is theorized that posterior capsule growth is halted after birth. In other tissues (e.g. blood vessels), cells tend to remodel their extracellular matrix toward some homeostatic biomechanical stress. Since, like the vasculature, the human lens is subjected to tension which varies with time, the LEC remodeling of the capsule may follow a similar mechanism. This tendency would explain the large thicknesses of the capsule of pig and cow lenses (∼60 µm even in young eyes) as follows. LECs proliferate in response to increased zonular tension in a stretch- and frequency-dependent manner.62 Approximate conservation of total epithelial cell count implies creation of a lens fiber cell as a result of each LEC proliferation event.63 Immature fiber cells rapidly expand their volume and surface64 area while also losing their organelles.61,65–71 Thus, an LEC proliferation event results in an increment in lens volume.
Continuous Curvilinear Capsulorhexis – A Practical Review
Published in Seminars in Ophthalmology, 2022
Creating a capsular window is a crucial step in cataract surgery. Mastering CCC is important to reduce complications and to achieve optimal anatomical and refractive results. Evolving technology provides alternatives to manual CCC, but these newer capsulotomy techniques also carry disadvantages, so manual CCC is still the gold standard. Understanding the physics of the lens capsule may help the surgeon anticipate its behavior during capsulorhexis, reduce complications and improve the outcomes. Currently, data regarding the long-term results of newer capsulotomy techniques such as femtosecond laser capsulotomy and precision pulse capsulotomy are limited. Future research is required to shed light on this topic. Cataract surgery should be tailored for each patient to get the best results.
Multimodal Imaging of a Severe Case of Neonatal Acute Retinal Necrosis and Lens Vacuoles Associated with Herpes Simplex Virus Infection
Published in Ocular Immunology and Inflammation, 2022
Takamasa Kinoshita, Akira Hatanaka, Junya Mori, Kei Akaiwa, Hiroko Imaizumi
By contrast, at initial examination, our patient had severe vacuoles with a peripheral circumferential arrangement and central involvement with inverted Y- or starfish-like configurations in both eyes. Some extremely fine vacuoles were detected near the anterior capsule. A histopathological study showed that the vacuoles had multi-lobulated cystoid formations resulting from swelling and rupture of cortical cells in the posterior cortex near the capsule.20 However, the authors also described that several layers of anterior cortical cells were similarly swollen, although they were not noticed clinically. In our patient, because the vacuoles near the anterior lens capsule were extremely small, a slit-lamp examination paying careful attention was needed to detect them. Whereas the number of vacuoles in the left eye gradually decreased with time, they instead transformed into large confluent cysts in the right eye. McCormick speculated that the vacuoles were caused by the temporary inability to metabolize one of the carbohydrates introduced into the diet.22 In our patient, retinal re-attachment with normal intraocular pressure was obtained in the left eye; whereas retrolental fibroplasia with low intraocular pressure developed in the right eye. The differences in eye conditions, including in aqueous humor production and lens metabolism, may have contributed to the asymmetricity in the progress of the vacuoles between both eyes.