A spatial statistic to determine appropriate field sampling size for linking image and field data

Proceedings of the 11th Australasian Remote Sensing and Photogrammetry Conference

Sampling and measurement methods for a study of childhood refractive error in a UK population

Background There is a paucity of data describing the prevalence of childhood refractive error in the United Kingdom. The Northern Ireland Childhood Errors of Refraction study, along with its sister study the Aston Eye Study, are the first population-based surveys of children using both random cluster sampling and cycloplegic autorefraction to quantify levels of refractive error in the United Kingdom. Methods Children aged 6–7 years and 12–13 years were recruited from a stratified random sample of primary and post-primary schools, representative of the population of Northern Ireland as a whole. Measurements included assessment of visual acuity, oculomotor balance, ocular biometry and cycloplegic binocular open-field autorefraction. Questionnaires were used to identify putative risk factors for refractive error. Results 399 (57%) of 6–7 years and 669 (60%) of 12–13 years participated. School participation rates did not vary statistically significantly with the size of the school, whether the school is urban or rural, or whether it is in a deprived/non-deprived area. The gender balance, ethnicity and type of schooling of participants are reflective of the Northern Ireland population. Conclusions The study design, sample size and methodology will ensure accurate measures of the prevalence of refractive errors in the target population and will facilitate comparisons with other population-based refractive data.

Quantifying the pathology of neurodegenerative disorders:Quantitative measurements, sampling strategies and data analysis

The use of quantitative methods has become increasingly important in the study of neurodegenerative disease. Disorders such as Alzheimer's disease (AD) are characterized by the formation of discrete, microscopic, pathological lesions which play an important role in pathological diagnosis. This article reviews the advantages and limitations of the different methods of quantifying the abundance of pathological lesions in histological sections, including estimates of density, frequency, coverage, and the use of semiquantitative scores. The major sampling methods by which these quantitative measures can be obtained from histological sections, including plot or quadrat sampling, transect sampling, and point-quarter sampling, are also described. In addition, the data analysis methods commonly used to analyse quantitative data in neuropathology, including analyses of variance (ANOVA) and principal components analysis (PCA), are discussed. These methods are illustrated with reference to particular problems in the pathological diagnosis of AD and dementia with Lewy bodies (DLB).

Tear film lipids:dynamic composition and clinical performance

Purpose: Meibomian-derived lipid secretions are well characterised but their subsequent fate in the ocular environment is less well understood. Phospholipids are thought to facilitate the interface between aqueous and lipid layers of the tear film and to be involved in ocular lubrication processes. We have extended our previous studies on phospholipid levels in the tear film to encompass the fate of polar and non-polar lipids in progressive accumulation and aging processes on both conventional and silicone-modified hydrogel lenses. This is an important aspect of the developing understanding of the role of lipids in the clinical performance of silicone hydrogels. Method: Several techniques were used to identify lipids in the tear film. Mass-spectrometric methods included Agilent 1100-based liquid chromatography coupled to mass spectrometry (LCMS) and Perkin Elmer gas chromatography mass spectrometry (GCMS). Thin layer chromatography (TLC) was used for separation of lipids on the basis of increasing solvent polarity. Routine assay of lipid extractions from patient-worn lenses was carried out using a Hewlett Packard 1090 liquid chromatograph coupled to both uv and Agilent 1100 fluorescence detection. A range of histological together with optical, and electron microscope techniques was used in deposit analysis. Results: Progressive lipid uptake was assessed in various ways, including: composition changes with wear time, differential lipid penetrate into the lens matrix and, particularly, the extent to which lipids become unextractable as a function of wear time. Solvent-based separation and HPLC gave consistent results indicating that the polarity of lipid classes decreased as follows: phospholipids/fatty acids > triglycerides > cholesterol/cholesteryl esters. Tear lipids were found to show autofluorescence—which underpinned the value of fluorescence microscopy and fluorescence detection coupled with HPLC separation. The most fluorescent lipids were found to be cholesteryl esters; histological techniques coupled with fluorescence microscopy indicated that white spots (’’jelly bumps’’) formed on silicone hydrogel lenses contain a high proportion of cholesteryl esters. Lipid profiles averaged for 30 symptomatic and 30 asymptomatic contact lens wearers were compiled. Peak classes were split into: cholesterol (C), cholesteryl esters (CE), glycerides (G), polar fatty acids/phospholipids (PL). The lipid ratio for ymptomatic/symptomatic was 0.6 ± 0.1 for all classes except one—the cholesterol ratio was 0.2 ± 0.05. Significantly the PL ratio was no different from that of any other class except cholesterol. Chromatography indicated that: lipid polarity decreased with depth of penetration and that lipid extractability decreased with wear time. Conclusions: Meibomian lipid composition differs from that in the tear film and on worn lenses. Although the same broad lipid classes were obtained by extraction from all lenses and all patients studied, quantities vary with wear and material. Lipid extractability diminishes with wear time regardless of the use of cleaning regimes. Dry eye symptoms in contact lens wear are frequently linked to lipid layer behaviour but seem to relate more to total lipid than to specific composition. Understanding the detail of lipid related processes is an important element of improving the clinical performance of materials and care solutions.

Novel tear film supplements:a potential application for synthetic protein-phospholipid complexes

Purpose: Surfactant proteins A, B, C and D complex with (phospho)lipids to produce surfactants which provide low interfacial tensions. It is likely that similar complexation occurs in the tear film and contributes to its low surface tension. Synthetic protein-phospholipid complexes, with styrene maleic anhydrides (SMAs) as the protein analogue, have been shown to have similarly low surface tensions. This study investigates the potential of modified SMAs and/or SMA-phospholipid complexes, which form under physiological conditions, to supplement natural tear film surfactants. Method: SMAs were modified to provide structural variants which can form complexes under varying conditions. Infrared spectroscopy and Nuclear Magnetic Resonance were used to confirm SMA structure. Interfacial behaviour of the SMA and SMA-phospholipid complexes was studied using Langmuir trough, du Nûoy ring and pulsating bubblemethods. Factors which affect SMA-phospholipid complex formation, such as temperature and pH, were also investigated. Results: Structural manipulation of SMAs allows control over complex formation, including under physiological conditions (e.g. partial SMAesterfication allowed complexation with dimyristoylphosphatidylcholine, at pH7). The low surface tensions of the SMAs (42mN/m for static (du Nûoy ring) and 34mN/m for dynamic (Langmuir) techniques) demonstrate their surface activity at the air-aqueous interface. SMA-phospholipid complexes provide even lower surface tensions (~2 mN/m), approaching that of lung surfactant, as measured by the pulsating bubblemethod. Conclusions: Design of the molecular architecture of SMAs allows control over their surfactant properties. These SMAs could be used as novel tear films supplements, either alone to complex with native tear film phospholipids or delivered as synthetic protein-phospholipid complexes.

Effect of a liposomal spray on the pre-ocular tear film

Purpose: With the potential to address evaporative dry eye, a novel spray has been developed in which phospholipid liposomes are delivered to the tear film via the surface of the closed eyelid. This study evaluated the short-term effects of liposomal spray application on the lipid and stability characteristics of the pre-ocular tear film in normal eyes. Methods: Twenty-two subjects (12M, 10F) aged 35.1 ± 7.1 years participated in this prospective, randomised, double-masked investigation in which the liposomal spray was applied to one eye, and an equal volume of saline spray (control) applied to the contralateral eye. Lipid layer grade (LLG), non-invasive tear film stability (NIBUT) and tear meniscus height (TMH) were evaluated at baseline, and at 30, 60, 90 and 135 minutes post-application. Subjective reports of comfort were also compared. Results: Treated and control eyes were not significantly different at baseline (p>0.05). Post-application, LLG increased significantly, at 30 and 60 minutes, only in the treated eyes (p=0.005). NIBUT also increased significantly in the treated eyes only (p<0.001), at 30, 60 and 90 minutes. TMH did not alter significantly (p>0.05). Comfort improved relative to baseline in 46% of treated and 18% of control eyes, respectively, at 30 minutes post-application. Of those expressing a preference in comfort between the eyes, 68% preferred the liposomal spray. Conclusions: Consistent with subjective reports of improved comfort, statistically and clinically significant improvements in lipid layer thickness and tear film stability are observed in normal eyes for at least an hour after a single application of a phospholipid liposomal spray.

The tear film and contact lens wear

Contact lenses have become a popular method of vision correction for millions of people globally. As with all devices designed for use within the body, interactions occur between the implanted material and the surrounding biological fluid. A common complaint of lens wearers is that they often experience symptoms of dry eye whilst wearing lenses. This sensation is often heightened towards the end of the day. Through the course of this study, various analytical techniques have been utilised including one dimensional electrophoresis and Western Blotting to study the protein profiles of tear samples. By studying the tears of non-contact lens wearers, it was possible to analyse what could be considered normal, healthy, individuals. A clinical study was also undertaken which followed a population of individuals from the neophyte stage to one whereby they were accustomed lens wearers. Tears were monitored at regular intervals throughout the course of this study and worn contact lenses were also analysed for proteins that had been deposited both on and within the lens. Contact lenses disrupt the tear film in a physical manner by their very presence. They are also thought to cause the normal protein profile to deviate from what would be considered normal. The tear film deposits proteins and lipids onto and within the lens. The lens may therefore be depriving the tear film of certain necessary components. The ultimate aim of this thesis was to discover how, and to what extent, lenses affected tear proteins and if there were any proteins in the tear fluid that had the potential to be used as biochemical markers. Should this be achievable it may be possible to identify those individuals who were more likely to become intolerant lens wearers. This study followed the changes taking place to the tear film as an effect of wearing contact lenses. Twenty-eight patients wore two different types of silicone hydrogel lenses in both a daily wear and a continuous wear regime. The tear protein profiles of the lens-wearers were compared with a control group of non-lens wearing individuals. The considerable amount of data that was generated enabled the clearly observable changes to the four main tear proteins to be monitored.

Tear protein interaction with hydrogel contact lenses

The design and synthesis of biomaterials covers a growing number of biomedical applications. The use of biomaterials in biological environment is associated with a number of problems, the most important of which is biocompatabUity. If the implanted biomaterial is not compatible with the environment, it will be rejected by the biological site. This may be manifested in many ways depending on the environment in which it is used. Adsorption of proteins takes place almost instantaneously when a biomaterial comes into contact with most biological fluids. The eye is a unique body site for the study of protein interactions with biomaterials, because of its ease of access and deceptive complexity of the tears. The use of contact lenses for either vision correction and cosmetic reasons or as a route for the controlled drug delivery, has significantly increased in recent years. It is relatively easy to introduce a contact lens Into the tear fluid and remove after a few minutes without surgery or trauma to the patient. A range of analytical techniques were used and developed to measure the proteins absorbed to some existing commercial contact lens materials and also to novel hydrogels synthesised within the research group. Analysis of the identity and quantity of proteins absorbed to biomaterials revealed the importance of many factors on the absorption process. The effect of biomaterial structure, protein nature in terms of size. shape and charge and pH of the environment on the absorption process were examined in order to determine the relative up-take of tear proteins. This study showed that both lysozyme and lactoferrin penetrate the lens matrix of ionic materials. Measurement of the mobility and activity of the protein deposited into the surface and within the matrix of ionic lens materials demonstrated that the mobility is pH dependent and, within the experimental errors, the biological activity of lysozyme remained unchanged after adsorption and desorption. The study on the effect of different monomers copolymerised with hydroxyethyl methacrylate (HEMA) on the protein up-take showed that monomers producing a positive charge on the copolymer can reduce the spoilation with lysozyme. The studies were extended to real cases in order to compare the patient dependent factors. The in-vivo studies showed that the spoilation is patient dependent as well as other factors. Studies on the extrinsic factors such as dye used in colour lenses showed that the addition of colourant affects protein absorption and, in one case, its effect is beneficial to the wearer as it reduces the quantity of the protein absorbed.

Tear and skin phospholipids:analysis and hydrogel analogues

This thesis is concerned with the analysis of phospholipids in the tear film and with the synthesis of phospholipids analogous to hydrogels. The work consists of two areas. The first area is the study of the phospholipids in the tear film, their nature and fate. The use of liquid chromatography mass spectrometry determined that the concentration of phospholipids in the tear film was less than previously thought. The analysis of the tear film phospholipids continued with thin layer chromatography. This showed the presence of diacylglycerides (DAGs) in the tear film at relatively high concentrations. The activity of an enzyme, phospholipase C, was found in the tear film. It was hypothesised that the low concentration of phospholipids and high concentrations of DAG in the tear film was due to the action of this enzyme. The second area of study was the synthesis of phospholipids analogous materials for use in ocular and dermal applications for use in ocular and dermal applications.For ocular applications the synthesis involved the use of the monomer N,N-dimethyl-N-(2-acryloylethyl)-N-(3-sulfopropyl) ammonium betaine (SPDA) in combination with 2-hdyroxyethyl methacrylate (HEMA). Charge-balanced membranes were also synthesised using potentially anionic monomers in conjunction with cationic monomers in stoichiometrically equivalent ratios also with HEMA as a commoner. Membranes of SPDA copolymers and charge-balanced copolymers proved to have some properties suitable for ocular applications. The dermal materials consisted of one family of partially hydrated hydrogels synthesised from SPDA in combination with ionic monomers: sodium 2-(acrylamido)-2-methyl propane sulfonate and acrylic acid-bis(3-sulfopropyl)-ester, potassium salt. A second family of partially hydrated hydrogels was synthesised from N-vinyl pyrrolidone in combination with the same ionic monomers. Both of the partially hydrated hydrogels synthesised proved to have some properties suitable for use as adhesives for the skin.

Some analytical aspects of sampling plans

This thesis reports on the results of the analyses of certain aspects of sampling inspection plans. The investigation has been confined to attributes (as distinct from variables) plans and in this respect.the analyses have been concerned with two main aspects of single and double plans. These are:- (i) the Average Outgoing Quality Limit (AOQL) of the plan. (ii) the Average Sample Number (ASN) of the plan. In the former connection the investigation has been concerned with the evaluation of the AOQL analytically and the determination of the fraction defective of the incoming material to give the AOQL. The analyses have been applied to both single and double sampling plans, In the latter connection the investigation has been concerned with the evaluation of the maximum ASN analytically and the determination of the fraction defective of the incoming material to give the maximum value of ASN. The analyses have been confined only to double sampling plans because in the case of single sampling the ASN is constant and is equal to n, the sample size.

Coherence imaging by use of a Newton rings sampling function

We show that, with suitable optics in the arm of a Michelson interferometer, orthogonal galvo-scanning mirrors build a sampling function in the form of Newton rings when the two interferometer arms are matched. Using a low-coherence source, one can obtain transversal depth-resolved images. A fast display procedure using a storage oscilloscope was devised based on this method.