Valerie Franklin

An in Vivo Comparison of the Kinetics of Protein and Lipid Deposition on Group Ii and Group Iv Frequent-replacement Contact Lenses

Purpose. To investigate the degree and rate of deposition of protein and lipid on FDA group II and group IV contact lens materials over a period of up to 28 days of wear. Methods. Twenty-two subjects wore a group IV lens (Acuvue) and a group II lens (Soflens 66) in a randomized, cross-over study. The lenses were randomly worn for periods between 1 and 28 days and then collected for laboratory-based deposition analysis. Results. The group II lenses revealed an increased degree of lipoidal spoilage (p < 0.0001) and the group IV lenses exhibited increased protein spoilage (p < 0.0001). Surface protein for both materials reached a maximum after 1 day and did not increase over the 4-week wearing period (p = NS). Total protein for group IV lenses reached a maximum between 1 and 7 days and then reached a plateau, with no further increase occurring (p = NS), whereas total protein accumulation on the group II lens continued to increase across all time periods (p < 0.05). Lipid deposition on the group IV lens was maximal after 1 day and increased no further (p = NS), whereas lipid deposition on the group II material monotonously increased and progressively built-up over the 4 weeks of wear (p < 0.0001). Conclusions. The kinetics of contact lens deposition is mediated by the chemical structure of the contact lens material under consideration. Protein deposition occurs rapidly with group IV materials before reaching a maximum, whereas N-vinyl pyrrolidone-containing group II materials progressively accumulate protein and lipid deposits, with no plateau occurring.

The osteo-odonto-keratoprosthesis (OOKP).

The osteo-odonto-keratoprosthesis (OOKP), although described over 40 years ago, remains the keratoprosthesis of choice for end-stage corneal blindness not amenable to penetrating keratoplasty. It is particularly resilient to a hostile environment such as the dry keratinized eye resulting from severe Stevens-Johnson syndrome, ocular cicatricial pemphigoid, trachoma, and chemical injury. Its rigid optical cylinder gives excellent image resolution and quality. The desirable properties of the theoretical ideal keratoprosthesis is described. The indications, contraindications, and patient assessment (eye, tooth, buccal mucosa, psychology) for OOKP surgery are described. The surgical and anaesthetic techniques are described. Follow-up is life-long in order to detect and treat complications, which include oral, oculoplastic, glaucoma, vitreo-retinal complications and extrusion of the device. Resorption of the osteo-odonto-lamina is responsible for extrusion, and this is more pronounced in tooth allografts. Regular imaging with spiral-CT or electron beam tomography can help detect bone and dentine loss. The optical cylinder design is discussed. Preliminary work towards the development of a synthetic OOKP analogue is described. Finally, we describe how to set up an OOKP national referral center.

CLEANING EFFICACY OF SINGLE-PURPOSE SURFACTANT CLEANERS AND MULTI-PURPOSE SOLUTIONS*

The initial stages of contact lens spoilation are rapid with respect to the deposition of tear components, in particular, lipids and proteins. In addition, extrinsic factors such as care solutions, cosmetics, skin lipids, drugs and tobacco smoke may all play an important part in the spoilation process. Care systems have different effects on this spoilation. Assessment of the relative cleaning efficacies of the single purpose and multipurpose cleaners which are now available in the UK (e.g. ReNu, Optifree, Complete), is of importance in understanding progressive contact lens-tear interactions. This paper furthers our understanding of the efficacies of these solutions in removing the deposition of tear components from the contact lens.

Patient-Dependent and Material-Dependent Factors in Contact Lens Deposition Processes

The interaction of polymers with the tears is conveniently studied by observing the nature of the contact lens surface contamination produced during wear. In developing analytical techniques capable of distinguishing between anterior and posterior surface deposition and between the different chemical species involved, the potential is established to use the lens as a probe for differences in patient-to-patient and eye-to-eye tear chemistry. In the broader context, the eye is an ideal body site to study the interactions between a complex biochemical system and an implantation material, both because of the ease of access and the fact that materials can be worn for a set period of time under known conditions before removal for analysis.

A model for the preliminary biological screening of potential keratoprosthetic biomaterials

A series of in vitro screening assays for the preliminary selection of biomaterials for use in the fabrication of artificial corneas (keratoprostheses) (KPros) have been investigated. These screening assays assessed the initial binding of inflammatory and cell adhesive proteins, activation of inflammatory proteins, adhesion of keratocytes, epithelial cells and macrophages and the production of inflammatory cytokines by keratocytes contacting biomaterials. Central optic biomaterials were selected on the basis of low-inflammatory and cell adhesion potential. Peripheral skirt materials were selected on the basis of low-inflammatory potential but good cell adhesion to anchor the implant within the host cornea. Green fluorescent protein (GFP) gene transfer was used in a novel context to investigate cell invasion in the absence of external staining techniques. Confocal laser scanning microscopy and scanning electron microscopy were used to investigate GFP positive keratocyte invasion of porous materials. The results of in vitro assays were compared to a corneal organ culture system in which the biomaterials were assessed within a stromal environment. A range of polyurethane-based interpenetrating polymers with a range of water contents were screened. All materials showed low-inflammatory potential. A reduction in biomaterial water content induced an increase in complement C3 and fibronectin binding and in cell adhesion to materials, whilst differences in co-monomer formulation had little impact. The screening methods used in the current study provide a suitable preliminary assessment regime for the in vitro evaluation of potential KPro materials.

Studies in the ocular compatibility of hydrogels (IV): observations on the role of calcium in deposit formation

Abstract Studies of the morphology and chemical composition of surface-located white inorganic films are described,together with the results of artificially raising the concentration of calcium ions absorbed within the lenses on the nature of the resultant spoilation. This type of white film is structurally heterogeneous and is composed of discrete crystals of calcium phosphate-carbonate overlaid by a lipid-rich organic layer, which is not chemically bound to the deposited inorganic layer, but shows elevated cholesterol ester levels consistent with an enhanced lid involvement with the rugous surface film. Elevated calcium levels within the lens matrix were found not to accelerate the rate of formation of conventional ‘white spot’ deposition.

Vitronectin Adsorption in Contact Lens Surfaces During Wear

There has been growing interest in recent years in the factors associated with inflammatory response in the eye. The possibility that different types of synthetic materials may enhance or modulate their response is now being given serious consideration. This has focused greater attention on tear biochemistry and the biochemical changes that result from the interaction of synthetic materials with the ocular environment. One such change involves vitronectin, now well established as an inflammatory marker in various body sites, having an important pro-active role in modulating the conversion of plasminogen to plasmin.1,2 The activation of plasminogen into plasmin is accepted as the most important mechanism of extracellular proteolysis and is consequently involved in localized inflammatory response and tissue repair.

Extrinsic factors in soft contact lens spoilation

T HE term contact lens spoliation is a broad, rather vague, expression that covers a wide variety of relatively complex chemicals and biochemical processes. It is possible to separate them into various categories. We could, for example, use any or all of the subdivisions listed in Table 1. One of the interesting (and sometimes daunting) features of spoilation by factors extrinsic to the eye (category IIA) is that it includes examples from each of the other categories IB-IG and IIB-IIG.

Controlled synthesis and processing of a poly(L-lactide-co-ε-caprolactone) copolymer for biomedical use as an absorbable monofilament surgical suture

Poly (L-lactide-co-ε-caprolactone) 75:25 % mol, P(LL-co-CL), was synthesized via bulk ring-opening polymerisation (ROP) using a novel tin (II) alkoxide initiator, [Sn (Oct)]2DEG, at 130°C for 48 hrs. The effectiveness of this initiator was compared withthe well-known conventional tin (II) octoateinitiator, Sn (Oct)2. The P(LL-co-CL) copolymersobtained were characterized using a combination of analytical technique including: nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), thermogravimetry (TG) and gel permeation chromatography (GPC). The P(LL-co-CL) was melt-spun into monofilament fibres of uniform diameter and smooth surface appearance. Modification of the matrix morphology was then built into the as-spun fibresvia a series of controlled off-line annealing and hot-drawing steps.

The potential influence of Schirmer strip variables on dry eye disease characterisation, and on tear collection and analysis

PURPOSE The use of the Schirmer strips (SS) as a tool in the characterisation of dry eye disease, depends upon the quantitative assessment of tear production and constituents. The aim of this study was to ascertain the extent to which the properties of commercially available SS can vary and the way in which this baseline information may relate to their comparability in clinical use. METHODS Five SS were analysed: Clement Clarke®, TearFlo®, Bio Schirmer®, Omni Schirmer® and JingMing®. Various aspects of their physical appearance and physicochemical behaviour were measured, including size, weight, and thickness together with surface morphology (assessed by SEM) and aqueous uptake and release behaviour (including the influence of each strip on protein retention and eluent osmolarity). RESULTS All physical parameters varied between the strips studied for example the Clement Clark was the largest, thickest, and heaviest strip assessed in this study. SEM images showed that each of the SS had unique surface morphologies. Statistically significant differences among the strips were found for uptake (p=0.001) and release volume (p=0.014). Clement Clarke absorbed the highest volume over a fixed time period (23.8±1.6μl) and Omni the lowest (19.3±0.5μl). Clement Clarke showing the highest eluent osmolarity value (5.0±0.0mOsm/L) and TearFlo the lowest (2.8±0.4mOsm/L). CONCLUSION The five strips investigated in this study indicate that there is no standardisation of commercial strips, despite the fact that the need for standardisation was recognised over fifty years ago. This study provides useful baseline information relating to SS comparability in clinical use.