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Ocular Drug Delivery Systems
Published in Ambikanandan Misra, Aliasgar Shahiwala, In-Vitro and In-Vivo Tools in Drug Delivery Research for Optimum Clinical Outcomes, 2018
Shubhini A. Saraf, Jovita Kanoujia, Samipta Singh, Shailendra K. Saraf
Primary Corneal Models: The outermost layer of anterior segment of the eye is known as corneal epithelium. Corneal epithelial cells isolated from rabbits are most frequently used to prepare a primary cell culture model. This model is very useful in studying drug permeation and active transport. Models of human primary epithelial cells are also used to study the drug absorption, ocular toxicity, and ocular irritation (Curren and Harbell 2002).
Corneal Endothelium Regeneration: Basic Concepts
Published in Gilson Khang, Handbook of Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine, 2017
The cornea is a highly organized transparent tissue and consists of five layers (epithelium, Bowman’s membrane, stroma, Descemet’s membrane, and endothelium), which are well established by function, as shown in Fig. 36.1.5 The corneal epithelium is the surface layer of the cornea, consisting of three types of cells (superficial cells, wing cells, and basal cells) connected by tight junctions. It provides a biodefense system from outer environment6 and forms an effective barrier against loss of fluid and pathogen penetration. Bowman’s membrane is a basement layer of the corneal epithelium and is located between the epithelium and the stroma.7 The stroma, locating between Bowman’s and Descemet’s membranes, constitutes about 90% of the cornea thickness and consists of the extracellular matrix (predominantly composed of collagen type I layers), keratinocytes, and nerve fibers.3,7 It effects physical properties such as strength, shape, stability, and transparency. In adults, Descemet’s membrane consists of two ultrastructurally distinct layers: an anterior band, later formed by highly organized collagen lamellae and proteoglycans, and a posterior band, which is a more amorphous layer. The anterior layer of Descemet’s membrane is formed during gestation and the total thickness is about 3 µm thick at birth.1 After birth, corneal endothelial cells synthesize the posterior layer of Descemet’s membrane and this layer continuously slowly increase throughout life, with an average thickness of 10 µm in older adults. Descemet’s membrane, the basal layer of the corneal endothelium, can grow up to 12 μm in thickness and mostly includes collagen types IV and VIII as well as various extracellular matrix factors such as fibronectin, vitronectin, laminins, and proteoglycans containing heparin sulfate, dematan sulfate, or keratin sulfate.3,8,9 The corneal endothelium is the innermost thin monolayer of the cornea, with a hexagonal shape and is laid on Descemet’s membrane. It is a physiologically important organ to maintain transparency of the cornea.
Natural Polymeric Scaffolds for Tissue Engineering Applications
Published in Journal of Biomaterials Science, Polymer Edition, 2021
The need to achieve a therapeutic effect has necessitated the use of frequent instillation of eye—drops [81,82]. Nonetheless, this is a challenge for patients having severe ocular surface diseases (OSD). Though several other approaches have been suggested [83,84], Kim et al. [85] recently utilized chemical-crosslinking and 1, 4—butanediol diglycidyl ether for the fabrication of a new HA membrane (HAM) to ensure effective treatment of OSD. This is because; the HAM sustainably releases HA for modulation of wound healing response in OSDs. Moreover, it is easy to apply with the ability to ensure sustained therapeutic action through its fitting ability to corneal curvature. HAM displayed desirable physical properties of easy manipulation, firmness, transparency and accurate fitting on ocular surface, all in its dry state. When hydrated, a resulting rapid swelling from the high retention occurred. Also, the application of HAM regulates the wound healing response in OSDs sustainably. Overall, HAM presents therapeutic effects in treatment of OSD, in addition to the safe and efficient properties from the primarily cultured human corneal epithelial cells. This addition of HAM improved the cell viability as well as expression of cell proliferation markers of the epithelial cells. This is as, the features of corneal epithelium healing, and reduced corneal limb vascularization, opacity and conjunctival fibrosis were associated with the presence of HAM.
Correlation of accommodation and lens location with higher-order aberrations and axial length elongation during orthokeratology lens wear
Published in International Journal of Optomechatronics, 2021
Jy-Been Liang, Wen-Pin Lin, Richard Wu, Connie Chen
Orthokeratology (OK) can correct up to moderate myopia and slow progression by overnight wearing of rigid gas permeable (RGP) contact lenses with a “reverse geometry” design, that is, a central flat curve and a very steep reverse curve.[1–4] Wearing overnight OK lenses results in an increase in the corneal surface, central corneal flattening, thinning of the central corneal epithelium, and thickening of the mid-peripheral cornea; the lenses flatten the apical radius of the cornea and restructure it toward an oblate-like ellipse as a result of their shape.[5] Flattening of the central cornea reduces corneal power, and thus corrects the myopic refractive error, and with the removal of the lenses on awakening, satisfactory unaided vision is achieved during the daytime.[1] The effect is similar to that of laser refractive surgery, such as photorefractive keratectomy (PRK) or laser in-situ keratomileusis (LASIK).
Agreement between anterior segment parameters obtained by a new ultrasound biomicroscopy and a swept-source fourier-domain anterior segment optical coherence tomography.
Published in Expert Review of Medical Devices, 2020
Xiuyuan Li, Pingjun Chang, Zhangliang Li, Shuyi Qian, Zehui Zhu, Qianwei Wang, Zhao Yun-E
The Insight-100 (ArcScan Inc., Golden, CO, USA) employs the high-frequency B-scan in the assessment of anterior segment parameters [24]. Anormal saline coupling medium is formed with adisposable eyepiece between the 50 MHz transducer and the eye. The instrument moves the transducer in an arc so that the beam axis maintains approximate normality to the surface of the eye. The frequencies of cornea, anterior chamber, and lens are 60 MHz, 50 MHz and 50 MHz, respectively. The maximum arc scanning range is 70 degrees [25], and there is alinear scanning range of 29mm. The axial and lateral resolutions are 35 μm and 65 μm, respectively. It can photograph the complete anterior segment from the corneal epithelium to the posterior capsule of the lens and measure its anatomical parameters.