Aisling Mann

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 fall and rise of tear albumin levels:a multifactorial phenomenon

Albumin in tears is used as a diagnostic marker of ocular insult and inflammation, but whether its presence in tears is responsive or part of an adaptive reaction remains unresolved. A review of the literature on tear albumin concentration emphasizes that variables such as collection method, stimulus, assay technique, and disease state influence the quoted values to different extents. Influence of assay technique is negligible in comparison to variation in sampling conditions. Ocular disease increases albumin concentrations but not in a specific manner. The literature review also highlighted that little systematic research has been carried out on the daily cycle of tear albumin levels. In order to remedy this shortcoming, we investigated variations in tear albumin concentration during the waking day. The concentration of albumin in 400 tear samples collected from 13 subjects was assessed at 2-hourly intervals throughout the waking day. Highest daytime albumin concentrations were obtained within 10 minutes of waking, with a mean concentration of >50 ± 22 μg/ml. Albumin levels were at their lowest, but most consistent, 2-6 hours post-waking. This pattern was followed by a progressive increase in albumin concentration during the latter part of the day. Although individual subject-to-subject concentration differences were observed, this distinctive pattern of diurnal variation was found in all subjects. The results presented suggest a regulated, not random, pattern of variation within the period of study.

The detection of kinin activity in contact lens wear.

Many factors can be, and have been, attributed to the appearance of complications in lens wear, but the greatest is associated with deposition. Reduced acuity, irritation and inflammatory responses are often referred to as adverse reactions arising as a result of deposition. In this study, particular attention was paid to the potential role of adsorbed proteins in activating, mediating and/or stimulating a host immune response, i.e., the hypothesis that the adsorption of certain proteins from the tears and ocular surfaces may actively affect successful lens wear. In particular, the purpose of this study was to investigate the presence of a group of proteins previously undiscovered in the ocular environment. The intention was to target a family of proteins/glycoproteins that have become prominent recently in a variety of inflammatory responses and disorders at many other mucosal associated sites around the body, e.g. in nasal rhinitis and in joint inflammation. The protein cascade in question is the kinin family of inflammatory mediators. The aim was to investigate their presence in the ocular environment, specifically in relation to contact lens wear, and consequently assess the implications of their discovery. High molecular weight kininogen (HMWK), with its central role in kinin responses, was investigated initially as the marker of kinin activity, with subsequent members examined thereafter.

The application of counter immunoelectrophoresis (CIE) in ocular protein studies. Part II:kinin activity in the lens wearing eye

The kinin family are a group of bioactive peptides that are closely involved in the modulation of vascular inflammation and local injury. We have demonstrated here, for the first time, a link between kinin activity and contact lens wear. Protein extracts from daily and extended wear etafilcon A, Group IV, Acuvue lenses (Vistakon), were analysed by counter immunoelectrophoresis. In this way, kinin activity associated with contact lens wear was detected. High molecular weight kininogen was used as the marker protein. In contrast, no kinin activity was detected in the non-lens wearing normal eye.

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.

Sulphonated biomaterials as glycosaminoglycan mimics in wound healing

This chapter considers the available evidence and underlying physicochemical principles that support the proposition that a biomimetic wound dressing based on glycosaminoglycan models offers a potential means of influencing wound bioactivity. Available evidence showing advantages in wound healing for experimental proteoglycanbased dressing materials is described, together with an overview of the bioactive role of sulphated macromolecules. This leads to an assessment of the analogies between the sulphonate group and the sulphate group and an explanation of their unique water binding behaviour. The available information suggests the desirability of an integrated physicochemical, biochemical and biological approach to the design and synthesis of new wound healing biomaterials.

The application of counter immunoelectrophoresis (CIE) in ocular protein studies. Part I: time dependent deposition patterns of immunoregulatory proteins on anionic hydrogel contact lenses.

This paper focuses on the effects of wear regime on the deposition pattern of important immunoregulatory proteins on FDA Group IV etafilcon-A lenses. Specifically, the aim was to assess the extent to which the daily disposable wear modality produces a different deposition of proteins from the conventional daily wear regime which is coupled with cleaning and disinfection. Counter immunoelectrophoresis (CIE) was employed to detect individual proteins in lens extracts from individual patients and focused on the analysis of five proteins, IgA, IgG, lactoferrin, albumin and kininogen. Deposition was monitored as a function of time; significantly lower deposition was detected on the daily disposable lenses.

Immunoblotting and Tear Sampling Techniques for the Study of Contact Lens-Induced Variations in Tear Protein Profiles

The role of extracellular nucleotides as signaling molecules is well established in a number of biological systems. Their function in the regulation of ion1, 2 and fluid3 transport has been investigated in the pigmented rabbit conjunctiva where active Cl− secretion has been implicated as the driving force for fluid secretion.3 These agonists interact with two classes of receptors located on the cell membrane: P2X ligand-gated ion channels and P2Y G-protein-coupled receptors.4 Receptor mapping techniques have revealed the presence of P2Y type receptors in ocular epithelial cells.5

Physicochemical properties of hydrogels for use in ophthalmology

This chapter deals with the physicochemical aspects of structure-property relationships in synthetic hydrogels, with particular reference to their application in optometry and ophthalmology. It demonstrates the ways in which the amount of water contained in the hydrogel network can be manipulated by changes in copolymer composition and illustrates the advantages and limitations imposed by use of water as a means of influencing surface, transport and mechanical properties of the gel. The chapter then illustrates how this basic understanding has formed a platform for the development of synthetic interpenetrating networks and macroporous materials, and of hybrids of natural and synthetic hydrogels. The behaviour of these more complex systems is not so centrally dominated by the equilibrium water content as is the case with homogeneous synthetic hydrogels, thus providing advantageous ways of extending the properties and applications of these interesting materials.

Ocular biotribology and the contact lens: Surface interactions and ocular response

Biotribology is essentially the study of friction, lubrication and wear in biological systems. The area has been widely studied in relation to the behaviour of synovial joints and the design and behaviour of hip joint prostheses, but only in the last decade have serious studies been extended to the eye. In the ocular environment - as distinct from articular joints - wear is not a major factor. Both lubrication and friction are extremely important, however; this is particularly the case in the presence of the contact lens, which is a medical device important not only in vision correction but also as a therapeutic bandage for the compromised cornea. This chapter describes the difficulty in replicating experimental conditions that accurately reflect the complex nature of the ocular environment together with the factors such as load and rate of travel of the eyelid, which is the principal moving surface in the eye. Results obtained across a range of laboratories are compared.