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The Biological Bases of Photoreception in the Process of Image Vision
Published in Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe, Visual and Non-Visual Effects of Light, 2020
Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe
The lens has just the right curvature for parallel rays of light to pass through each of its parts and be bent exactly enough for all the rays to pass through a single focal point. The more a lens bends the light rays, the greater is its refractive power measured in terms of diopters. In children, this refractive power can be increased from 20 diopters to about 34 diopters, which is an accommodation of about 14 diopters. The elastic lens capsule can change shape (become more or less spherical) in response to the activity of the ciliary muscle, controlled by the autonomic nervous system. This refractive power influences visual acuity, or clarity of vision – in the human eye it is about 25 seconds of arc for discriminating between point sources of light. A person with normal visual acuity looking at two pinpoint light spots 10 m away can barely distinguish the separate spots when they are 1.5 to 2 mm apart.
Formulation of Depot Delivery Systems
Published in Sandeep Nema, John D. Ludwig, Parenteral Medications, 2019
Christopher A. Rhodes, Nikita Malavia
The bioerodible dexamethasone implant drug delivery device is implanted in the lens capsule at the time of surgery (a few seconds required for implantation; no additional procedure required) and releases dexamethasone either over 2 weeks (IVMED-10 for routine cases) or 6 weeks (IVMED-20 for complex cases, such as patients with diabetes or preexisting inflammation). Its PLGA matrix degrades by hydrolysis shortly thereafter and does not alter the transparency of the intraocular lens. It is peripheral to the lens and does not migrate in the rest of the eye as it is enveloped by the capsule. It is the only drug delivery device to rest within the lens capsule of the eye, and may be the only system capable of bidirectional drug delivery to both the front and back segments of the eye.
Eye tissue regeneration and engineering
Published in David M. Gardiner, Regenerative Engineering and Developmental Biology, 2017
Konstantinos Sousounis, Joelle Baddour, Panagiotis A. Tsonis *
The lens is the organ that focuses the light to the retina. It is composed of three main parts: the lens capsule that surrounds the whole organ, epithelial cells in the anterior side, and fibers in the posterior side and core (Figure 24.3). Epithelial cells proliferate and differentiate to lens fibers at the bow region throughout life. The most common lens disease is cataract, which is a generic word used to describe the obstruction of the light’s path. Cataracts have many etiologies but mainly involve the deregulation of crystallins, the major proteins found in lenses (Francis et al. 1999; Sousounis and Tsonis 2012). Cataract surgery restores the light’s path, and the implantation of an intraocular lens (IOL) inside the lens’ capsule restores part of the optic power. The IOLs are the most permanent, effective, and convenient way to restore sight compared with the previously used bulky and thick glasses or troublesome contact lenses (Asbell et al. 2005). These implants are made from different materials, including polymethyl methacrylate (PMMA), silicone, hydrophobic or hydrophilic foldable acrylic, and Collamer. Implant coating is one area that can benefit from material engineers’ input. Heparin-coated IOLs have been successfully used to reduce inflammation after the operation (Krall et al. 2014). Based on the pathophysiology of the disease in a patient-specific manner, coated IOLs may increase the success rate of the procedure and prevent unwanted side effects.
Repeatability and reproducibility of anterior lens zonule length measurement using ArcScan insight 100 very high-frequency ultrasound
Published in Expert Review of Medical Devices, 2023
Zehui Zhu, Han Zou, Hongzhe Li, Xueer Wu, Yiyi Wang, Zhangliang Li, Yune Zhao
Most published studies using the Insight 100 have focused on phakic IOL implantation. Accurate measurements of the anterior eye segment’s anatomy play a critical role in selecting the appropriate IOL size before surgery [6,10,11]. Anterior segment optical coherence tomography (AS-OCT) and ultrasound devices are utilized for measuring various anterior segment structural parameters, including anterior chamber depth, anterior chamber angle distance, sulcus-to-sulcus, and other relevant metrics. AS-OCT enables swift image acquisition and high-resolution scans. However, it is limited by its inability to display the ciliary body, ciliary sulcus, and the complete space between the iris and the crystalline lens with clarity. In comparison to AS-OCT, the Insight 100 examination procedure is notably more intricate and requires additional time. However, the primary benefit of utilizing Insight 100 is its ability to produce highly precise images of the entire anterior ocular segment, which includes the ciliary muscle, the equator of the lens, and the posterior lens capsule.
Numerical modelling to assess the tear force of human capsulotomy margin
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
The lens capsule is a thin and elastic membrane. The tear resistance of the capsulotomy edge directly affects the subsequent installation of the IOL, thereby affecting the clinical treatment outcomes (Cekic and Batman 1999). Research on the tear force of the capsule edge can contribute to understand the mechanism the capsule rupture, which improves the safety of the entire surgery. The purpose of this study is to discuss the material parameters of capsule, and motion and model parameters of retractor to affect the tear force of the capsule edge. Hence, a FE model of lens capsule stretching, which contains capsule and two retractors, was developed to quantitatively analyze the tear force.