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Microbial Biofilms
Published in Chaminda Jayampath Seneviratne, Microbial Biofilms, 2017
Chaminda Jayampath Seneviratne, Neha Srivastava, Intekhab Islam, Kelvin Foong and Finbarr Allen
Bacterial biofilms have been demonstrated on materials relevant to the eye such as contact lenses, scleral buckles, suture material and intraocular lenses. Many ocular infections often occur when such prosthetic devices come in contact with or are implanted in the eye. Approximately 56% of corneal ulcers in the United States are associated with contact lens wear [89]. Because of their proximity to the cornea, contact lenses may modify and compromise the corneal epithelium and make it easier for microorganisms in the vicinity to adhere to the ocular surfaces [90]. Continuous contact of the eye with the biofilm-infested lens may lead to serious ocular conditions such as endophthalmitis and keratitis [91,92]. The physical properties and surface chemistry of contact lenses can influence the variation in adherence of organism onto it. For instance, in vitro studies have shown that silicone hydrogel lenses have a greater propensity to biofilm formation than hydroxyethyl methacrylate–based soft lenses [93]. In particular, more hydrophobic surfaces of silicone hydrogel facilitate P. aeruginosa biofilm formation. In addition, during contact lens wear, a protein-rich coating or conditioning film derived from host products forms on the contact lens surface. Such conditioning films have been found to influence the microbial adherence [93].
Contact lenses
Published in Pablo Artal, Handbook of Visual Optics, 2017
Unfortunately, silicone elastomer lenses had one undesirable and potentially dangerous flaw; their rubberlike nature generated negative pressure under the lens when worn and resulted in the lens sticking to the eye (Fanti and Holly 1980, Josephson and Caffery 1980). This phenomenon could not be overcome with design, and so the industry set about generating a hybrid material, a silicone–hydrogel: part silicone and part hydrogel. Although seemingly straightforward, the material scientists were essentially trying to mix “oil and water” and still maintain a transparent material. Bausch + Lomb, the first company to bring soft hydrogel contact lenses to the market in 1971, were also the first to develop a commercially viable silicone–hydrogel lens. This lens provided more than four times the oxygen transmission of hydrogel lenses, approved for up to 30 days of continuous wear and was first available in 1999. Clinicians immediately noted that the highly oxygen transmissive lenses eradicated significant adverse responses related to lack of oxygen at the cornea but were wary about using silicone–hydrogel lenses due to the up to 30 days of continuous wear indication awarded by the FDA. Experience over the years with extended wear of hydrogel lenses had shown that corneal ulcers or microbial keratitis was the single most significant adverse response associated with extended or continuous wear, with the FDA limiting wear time approval of all hydrogel lenses to seven nights maximum in 1989 due to their concern at the incidence levels (Schein et al. 1989). The industry hoped that the introduction of silicone hydrogels would eliminate the risk of microbial keratitis, but worldwide postmarket surveillance studies have shown that significantly increased oxygen transmission does not reduce the risk of microbial keratitis associated with the overnight wear of contact lenses (Schein et al. 2005). Clinicians and companies now recommend silicone–hydrogel lenses for daily wear or extended wear with monthly replacement, and the largest area of growth within the contact lens industry is in the daily-wear modality.
Efficacy of two silicone-hydrogel bandage contact lenses after corneal crosslinking
Published in Clinical and Experimental Optometry, 2021
Deniz Ozarslan Ozcan, Sait Coskun Ozcan
Corneal epithelial healing is often supported with the use of bandage contact lenses in clinical practice. A constant supply of oxygen is required to ensure the health and repair of the corneal epithelium. Extended wear contact lenses should have a value of approximately 125 oxygen transmissibility (Dk/t) to prevent corneal anoxia.16 SiH contact lenses provide a high Dk/t with a range of 110 to 175 due to their silicone component content. Soft lenses have beneficial properties such as covering the entire corneal surface and providing patient comfort with their soft structure. In addition to these properties considerably high oxygen permeability is the most important advantage of the silicone hydrogel lenses in therapeutic use. Taneri et al.17 showed that soft contact lenses had clinically meaningful therapeutic effects on epithelial healing, pain perception, visual recovery and haze formation after PRK.
Medicated ocular bandages and corneal health: potential excipients and active pharmaceutical ingredients
Published in Pharmaceutical Development and Technology, 2018
Ghada Zidan, Ilva D. Rupenthal, Carol Greene, Ali Seyfoddin
Silicone hydrogel contact lenses were introduced in the late 90s and gained high popularity since then due to their high oxygen permeability compared to polymeric hydrogels. This makes them suitable for use as extended wear contact lenses up to 30 days. Silicone hydrogel lenses are usually composed of siloxane macromer for enhanced oxygen permeability, that is copolymerized with a hydrogel phase consisting of a hydrophobic monomer such as tris[trimethylsiloxy]silylpropylmethacrylate (TRIS) and a hydrophilic monomer such as (N,N-dimethylacrylamide) (DMA), N-vinyl pyrrolidone (NVP), or HEMA. The hydrogel phase increases the lens wettability which is essential for comfort, adequate lens movement, and sufficient ion transfer. Silicone hydrogel contact lenses can be used to deliver ophthalmic drugs to the eye with controlled release of medication from 20 days up to more than 3 months depending on the ratio between the hydrophobic and hydrophilic components (Kim et al. 2008).
Impact of contact lens material and design on the ocular surface
Published in Clinical and Experimental Optometry, 2018
Javier Ruiz‐alcocer, Daniel Monsálvez‐romín, Santiago García‐lázaro, César Albarrán‐diego, José Luis Hernández‐verdejo, David Madrid‐costa
New contact lens materials are continually being introduced into the market. In order to obtain lower rates of discontinuation, manufacturers constantly strive to develop lenses that minimise ocular surface complications and increase user comfort. At the same time, it has been demonstrated that daily disposable contact lenses have eliminated several problems related to continuous wear and that their use is significantly increasing worldwide.7 For this reason, great efforts have been made to improve these lens types, including the aforementioned introduction of a new conventional hydrogel with a 78 per cent water content. The behaviour of this novel, high water content hydrogel lens was compared with two other lenses made with silicone hydrogel.