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Design principles for corneal implants are challenging and include permeability which inherently involves pore openings on the polymer surface. These topographical cues can be significant to a successful clinical outcome where a stratified epithelium is needed over the device surface, such as with a corneal onlay or corneal repair material. The impact of polymer surface topography on the growth and adhesion of corneal epithelial tissue was assessed using porous perfluoropolyether membranes with a range of surface topography. Surfaces were characterised by AFM and XPS, and the permeability and water content of membranes was measured. Biological testing of membranes involved a 21-day in vitro tissue assay to evaluate migration, stratification and adhesion of corneal epithelium. Similar parameters were monitored in vivo by surgically implanting membranes into feline corneas for up to 5 months. Data showed optimal growth and adhesion of epithelial tissue in vitro when polymer surface features were below a 150 nm RMS value. Normal processes of tissue growth and adhesion were disrupted when RMS values approached 300 nm. Data from the in vivo study confirmed these findings. Together, outcomes demonstrated the importance of surface topography in the design of implantable devices that depend on functional epithelial cover., (Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.)

This study assessed the long-term biological response of a perfluoropolyether-based polymer developed as a corneal inlay to correct refractive error. The polymer formulation met chemical and physical specifications and was non-cytotoxic when tested using standard in vitro techniques. It was cast into small microporous membranes that were implanted as inlays into corneas of rabbits (n = 5) and unsighted humans (n = 5 + 1 surgical control) which were monitored for up to 23 and 48 months respectively. Overall, the inlays were well tolerated during study period with the corneas remaining clear and holding a normal tear film and with no increased vascularisation or redness recorded. Inlays in three human corneas continued past 48 months without sequelae. Inlays in two human corneas were removed early due to small, focal erosions developing 5 and 24 months post-implantation. Polymer inlays maintained their integrity and corneal position for the study duration although the optical clarity of the inlays reduced slowly with time. Inlays induced corneal curvature changes in human subjects that showed stability with time and the refractive effect was reversed when the inlay was removed. Outcomes showed the potential of a perfluoropolyether inlay as a biologically acceptable corneal implant with which to provide stable correction of refractive error., (Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.)

Purpose: To identify a rapid and effective tear collection method providing sufficient tear volume and total protein content (TPC) for analysis of individual proteins in cats., Methods: Domestic adult short-haired cats (12-37 months; 2.7-6.6 kg) were used in the study. Basal tears without stimulation and eye-flush tears after instillation of saline (10 μl) were collected using microcapillary tubes from animal eyes either unwounded control or wounded with 9-mm central epithelial debridement giving four groups with n = 3. Tear comparisons were based on total time and rate for tear collection, TPC using micro bicinchoninic acid (BCA), tear immunoglobulin A (IgA), total matrix-metalloproteinase (MMP)-9 concentration using sandwich enzyme-linked immunosorbent assay (ELISA) and MMP-9 activity., Results: Eye-flush tears were collected significantly faster than basal tears in wounded eyes with higher rates for tear collection in unwounded control and wounded eyes. TPC was significantly lower in eye-flush tears compared to basal tears. The relative proportion of tear IgA normalized to TPC (% IgA of TPC) was not significantly different between basal and eye-flush tears. In unwounded control eyes, MMP-9 was slightly higher in eye-flush than in basal tears; activity of MMP-9 in both tear types was similar. In wounded eyes, eye-flush tears showed highest MMP-9 levels and activity on Day 1, which subsequently decreased to Day 7. MMP-9 activity in basal tears from wounded eyes did not display changes in expression., Conclusions: Eye-flush tears can be collected rapidly providing sufficient tear volume and TPC. This study also indicates that eye-flush tears may be more suitable than basal tears for the analysis of MMPs following corneal wounding., (© 2011 The Authors. Acta Ophthalmologica © 2011 Acta Ophthalmologica Scandinavica Foundation.)

Silicone hydrogel contact lenses, which have been a major advance in the field of vision correction, require surface modification or coatings for comfort and biocompatibility. While current coatings show adequate clinical performance, advanced coatings may improve the biocompatibility of contact lenses further by reducing biofouling and related adverse clinical events. Here, we have produced coatings on Lotrafilcon A contact lenses by deposition of a thin film of allylamine plasma polymer (ALAPP) as a reactive interlayer for the high density grafting of poly(ethylene oxide) dialdehyde (PEO(ALD)(2)), which had previously shown complete resistance to protein adsorption in vitro. The performance of these contact lenses was evaluated in a controlled clinical study over 6h using Focus Night and Day (also known as Air Optix Night & Day) contact lenses as control lenses. Surface modified lenses were characterised by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) before and after wear. Clinical data showed a high level of biocompatibility of the PEO coated lenses equivalent to control lenses. Surface analysis of worn contact lenses demonstrated that the high density PEO coating is effective in reducing biofouling in vivo compared to control lenses, however small amounts of protein deposits were still detected on all worn contact lenses. This study highlights that elimination of biofouling in vivo can be much more demanding than in vitro and discusses issues that are important for the analysis of worn contact lenses as well as the design of improved contact lenses., (Crown Copyright (c) 2010. Published by Elsevier Ltd. All rights reserved.)

For 30 years, contact lens research focused on the need for highly oxygen-permeable (Dk) soft lens materials. High Dk silicone hydrogel contact lenses, made available in 1999, met this need. The purpose of this review is to examine how silicone hydrogel lens wear affects the ocular surfaces and to highlight areas in which further research is needed to improve biocompatibility. Silicone hydrogel lenses have eliminated lens-induced hypoxia for the majority of wearers and have a less pronounced effect on corneal homeostasis compared to other lens types; however, mechanical interaction with ocular tissue and the effects on tear film structure and physiology are similar to that found with soft lens wear in general. Although the ocular health benefits of silicone hydrogel lenses have increased the length of time lenses can be worn overnight, the risk of infection is similar to that found with other soft lens types, and overnight wear remains a higher risk factor for infection than daily wear, regardless of lens material. Future contact lens research will focus on gaining a better understanding of the way in which contact lenses interact with the corneal surface, upper eyelid, and the tear film, and the lens-related factors contributing to infection and inflammatory responses.

Contact lenses made from materials of low-oxygen permeability (Dk) do not meet the oxygen requirements of the cornea for overnight wear. Long-term extended wear of these lenses results in chronic changes to all layers of the cornea, many of which are associated with hypoxia. High-Dk silicone hydrogel and gas permeable lenses are now available for 30-night continuous wear. The high-oxygen transmissibilities of these lenses have enabled the development of a successful continuous wear modality by eliminating the hypoxic effects of long-term wear. Presently, the focus is on improving lens performance by developing lenses that are more biocompatible, provide greater comfort, and maintain a stable tear film without inflammatory or mechanically induced adverse events.

Purpose: This study evaluated an improved perfluoropolyether polymer formulation designed for use as a corneal onlay to correct refractive error., Methods: Collagen I coated perfluoropolyether lenticules were implanted in feline corneas exposing a 6-mm diameter area of lenticule surface for epithelial growth. A parallel series of sham-wounded corneas were also studied. All corneas were monitored clinically for 4 or 8 weeks after surgery when animals were terminated and corneas used for histology with light and electron microscopy., Results: Postoperative epithelial growth began on days 1 and 2. Lenticule surfaces were fully epithelialized by days 5 to 11. Corneas remained clear, and the lenticules maintained epithelial cover until the designated time points. Histology of the implanted corneas showed that the lenticules were well tolerated by the cornea. Each lenticule was fully covered by a multilayered epithelium with microvilli, desmosomes, and a differentiated basal cell layer. Epithelial adhesive structures (basal lamina, hemidesmosomes, and anchoring fibrils) had assembled at the tissue-lenticule interface., Conclusions: Collagen coated perfluoropolyether lenticules implanted in the feline cornea supported the growth of a stable stratified squamous epithelium. These encouraging results are a step further in the development of a corneal onlay for correction of refractive error.