Aim: The aim of this study was to establish normal values for Schirmer tear test (version 2) and tear break up time (TBUT) in a South African young adult Black population. Method: Following ethical approval by the biomedical research and ethics committee, KwaZulu-Natal, participants were recruited from the city of Durban in South Africa via personal invitations, poster advertisements and University of KwaZulu-Natal optometry clinic clients. McMonnies questionnaire for dry eye diagnosis was administered and those who failed were excluded from the main study. Two hundred (100 males and 100 females) participants who met the inclusion criteria were included in the study. Following a slit lamp examination of the eye, the Schirmer test was administered and the following day, the TBUT was measured. A re-test version of the two procedures were conducted one week after, at about the same time of the day for each subject. Results: The participants were aged 18-30 years, mean = 20.77 ± 2.29 years. The mean Schirmer test values for all participants (N = 200; 400 eyes) was 15.96 ± 6.86mm. The values for the males and females (200 eyes each) were 16.34 ± 6.93mm and 15.58 ± 6.81mm respectively. The mean TBUT (400 eyes) was 7.18 ± 1.89 secs. The mean values for the males and females (200 eyes each) were 6.90 ± 1.88 secs and 7.32 ± 1.67 secs respectively. A strong positive correlation (r = 0.895) and (r = 0.914) respectively was found between the right and left eyes in the two tests. Conclusion: Generally, the mean values found in this study for the Schirmer test are similar to those that have been reported in the literature. However, values for TBUT differ from the values that have been previously reported, being higher in some instances and lower in others. These findings have implications for dry eye diagnosis and also contact lens practice in South Africa. / Thesis (M.Optom.)-University of KwaZulu-Natal, Westville, 2012.

Purpose To examine soft contact lens fitting characteristics using anterior segment imaging techniques and comfort. The specific aims of each chapter are as follows: Chapter 2: To calibrate the new ZEISS VisanteTM anterior segment optical coherence tomographer (OCT) using references with known physical thickness and refractive index equal to the human cornea and to compare the Visante measures to those from a previous generation OCT (Zeiss-Humphrey OCT II). Chapter 3: The first purpose of this study was to measure the repeatability of the Visante TM OCT in a normal sample. The second was to compare corneal thickness measured with the Visante TM OCT to the Zeiss-Humphrey OCT II (model II, Carl Zeiss Meditec, Jena Germany) adapted for anterior segment imaging and to the Orbscan II TM (Bausch and Lomb, Rochester New York). Chapter 4: Conjunctival displacement observed with the edges of the contact lens, when imaged may be real or may be an artefact of all OCT imagers. A continuous surface appears displaced when the refractive index of the leading medium changes at the edge of a contact lens. To examine this effect, edges of the contact lenses were imaged on a continuous surface using the UHR-OCT. Contact lens edges on the human conjunctival tissue were also imaged to see if the lens indentation on the conjunctival tissue is real or an artefact at the edge of the lens. Chapter 5: The main purpose of this study was to determine if we can predict end of the day discomfort and dryness using clinical predictive variables. The second purpose of the study was to determine if there was any relationship between lens fitting characteristics and clinical complications and especially to the superior cornea and conjunctiva with a dispensing clinical trial. Methods Chapter 2: Twenty two semi-rigid lenses of specified thicknesses were manufactured using a material with refractive index of 1.376. Central thickness of these lenses was measured using VisanteTM OCT and Zeiss-Humphrey OCT II (Zeiss, Germany). Two data sets consisting of nominal measures (with a standard pachymeter of the lenses and one obtained using a digital micrometer) were used as references. Regression equations between the physical and optical (OCT) measures were derived to calibrate the devices. Chapter 3: Fifteen healthy participants were recruited. At the Day 1 visit the epithelial and total corneal thickness, across the central 10mm of the horizontal meridian were measured using the OCT II and the Visante TM OCT. Only total corneal thickness across the central 10mm of the horizontal meridian was measured using the Orbscan II. The order of these measurements was randomized. These measurements were repeated on Day 2. Each individual measurement was repeated three times and averaged to give a single result. Chapter 4: (2-D) Images of the edges of marketed silicone hydrogel and hydrogel lenses with refractive indices (n) ranging from 1.41-1.51 were taken placing them concave side down on a continuous surface. Five images for each lens were taken using a UHR-OCT system, operating at 1060 nm with ~3.2um (axial) and 10μm (lateral) resolution at the rate of 75,000 A-scans/s. The displacement of the glass slide beneath the lens edge was measured using Image J. Chapter 5: Thirty participants (neophytes) were included in the study and the four lenses (Acuvue Advance 8.3, Acuvue Advance 8.7, Pure Vision 8.3, and Pure Vision 8.6) were randomly assigned for each eye. The lenses were worn for a period of two weeks on a daily wear basis for 8 to 10hrs per day. Lens performance was monitored over the 2week period. Assessment of subjective comfort was made using visual analogue scales. Total corneal and epithelium thickness was measured using the Visante OCT, the lens edge profiles of the contact lenses were observed using the ultra-high resolution OCT and the conjunctival epithelial thinning was measured using the RTVue OCT. Conjunctival blood velocity was measured at the baseline and 2 week visit using a high magnification camera. Results Chapter 2: Before calibration, repeated measures ANOVA showed that there were significant differences between the mean lens thicknesses from each of the measurement methods (p<0.05), where Visante measurements were significantly different from the other three (OCT II, MG and OP) methods (p<0.05). Visante thickness was significantly higher than the microgauge measures (453±37.6 µm compared to 445.1±38.2 µm) and the OCT II was significantly lower (424.5±36.1 µm both, p<0.05). After calibration using the regression equations between the physical and optical measurements, there were no differences between OCT II and Visante OCT (p<0.05). Chapter 3: Mean central corneal and epithelial thickness using the Visante™ OCT after calibration at the apex of the cornea was 536± 27 µm (range, 563-509 µm) and 55± 2.3 µm (range, 57.3-52.7 µm), respectively. The mean corneal and epithelial thickness using OCT II at the apex was 520±25µm and 56±4.9 µm, respectively. The mean of total corneal thickness measured with the Orbscan II was 609±29µm. Visante OCT was the most repeatable for test-retest at the apex, nasal and temporal quadrants of the cornea compared to OCT II and Orbscan II. COR’s of Visante OCT ranged from ±7.71µm to ±8.98µm for total corneal thickness and ± 8.72 µm to ± 9.92 µm for epithelial thickness. CCC’s with Visante OCT were high for total corneal thickness for test-retest differences ranging from 0.97 to 0.99, CCC’s for epithelial thickness showed moderate concordance for both the instruments. Chapter 4: Results showed that artefactual displacement of the contact lens edge was observed when the lenses were imaged on the glass reference sphere, custom made rigid contact lenses (1.376) and on the conjunctival tissue. The displacement measured on the conjunctival tissue ranged from 7.0±0.86 µm for the Air Optix Night and Day to 17.4±0.22 µm for the Acuvue Advance contact lenses. The range of displacement with the soft lens edges imaged on the rigid contact lens was from 5.51±0.03 µm to 9.72±0.12 µm. Chapter 5: The lenses with the steepest sag (Acuvue Advance 8.3, Pure Vision 8.3) resulted not only with the tightest fit, but with compromise to the superior conjunctiva. This was especially seen with the Acuvue Advance lenses. The steeper lenses caused more total corneal swelling, superior epithelial thinning, mechanical compression of conjunctiva, conjunctival staining, bulbar hyperemia, conjunctival indentation and reduced blood flow at the lens edge. Not many associations were observed between baseline clinical and 2 weeks sensory variables. However, significant associations were observed when comparing the baseline clinical variables to end of the day sensory variables. Baseline clinical variables compared to 2 week clinical variables also showed significant correlations. Conclusions Chapter 2: Using reference lenses with refractive index of the cornea (1.376) allows rapid and simple calibration and cross calibration of instruments for measuring the corneal thickness. The Visante and OCT II do not produce measurements that are equal to physical references with refractive index equal to the human cornea. Chapter 3: There is good repeatability of corneal and epithelial thickness using each OCT for test-retest differences compared to the between instruments repeatability. Measurements of epithelial thickness are less repeatable compared to the total corneal thickness for the instruments used in the study. Chapter 4: When contact lenses are imaged in-situ using UHR-OCT the conjunctival tissue appeared displaced. This experiment indicates that this displacement is an artefact of all OCT imagers since a continuous surface (glass slide) was optically displaced indicating that the displacement that is observed is a function of the refractive index change and also the thickness of the contact lens edges. Chapter 5: Discomfort is a complex issue to resolve since it appears to be related to ocular factors such as the corneal and conjunctival topography and sagittal depth; to lens factors that is 1) how the sag depth of the lenses relate to the corneal/conjunctival shape and depth and therefore how well it moves on the eye. 2) Also with the lens material; whether they are high or low modulus, low or high water content, dehydration properties, wetting agents used and its resistance to deposits, lens edge profile and thickness and its interaction with the upper eyelid.

Purpose To study the impact of lactoferrin and lipids on the kinetic deposition and denaturation of lysozyme on contact lens materials. Methods The contact lenses investigated in this thesis included two silicone hydrogel lenses [AIR OPTIX AQUA; lotrafilcon B and ACUVUE OASYS; senofilcon A] and two conventional hydrogel lenses [ACUVUE 2; etafilcon A and PROCLEAR; omafilcon A]. All lenses were incubated in four solutions: a complex artificial tear solution (ATS); an ATS without lactoferrin; an ATS without lipids; and an ATS without lactoferrin and lipids. Following various time points, all lenses were prepared for lysozyme analysis using the methods below: • To quantify the kinetic uptake of lysozyme to different contact lens materials, I125-radiolabelled lysozyme was added to each incubation solution. Total lysozyme deposition was quantified using a gamma counter. • To study the activity of lysozyme deposited to contact lenses, a fluorescence-based lysozyme activity assay was compared to a turbidity assay. Potential interactions with lens materials and extraction solvents were evaluated. • To investigate the kinetic denaturation of lysozyme deposited to different contact lens materials, the fluorescence-based activity assay and the enzyme-linked immunosorbent assay were used. Results The presence of lactoferrin and lipids decreased lysozyme uptake to lotrafilcon B. Lysozyme deposition on senofilcon A was greater in the absence of lipids after day 21, however the opposite was seen with etafilcon A, where lysozyme uptake was lower without lipids in the ATS. Lactoferrin and/or lipids had no effect on lysozyme adsorption to omafilcon A. The fluorescence-based lysozyme activity assay demonstrated high sensitivity and a wide linear range of detection, which covers the amount of lysozyme typically extracted from contact lenses. Using this assay, lysozyme activity on both silicone hydrogel materials was lower in the presence of lipids in the ATS. In addition, lactoferrin had a protective effect on lysozyme activity for lysozyme sorbed to senofilcon A. Moreover, the presence of lactoferrin and/or lipids did not exhibit any effect on lysozyme denaturation with conventional hydrogel lenses. Conclusions The presence of lactoferrin and lipids in an artificial tear solution impacted lysozyme deposition and denaturation of lysozyme on various contact lenses. It is important for in vitro studies, when developing tear film models, to consider the effects of tear film components when investigating protein deposition and denaturation on contact lenses.

Contact Lens Acute Red Eye (CLARE) and Infiltrative Keratitis (IK) are inflammatory responses of the eye associated with extended wear of soft contact lenses. Bacterial colonization of contact lenses with Gram-negative bacteria such as Pseudomonas aeruginosa is an important risk factor for the development of these adverse responses. Strategies that control the bacterial colonization of contact lenses may help prevent the occurrence of adverse responses. This thesis aimed to develop an animal model of CLARE/IK to test this hypothesis and to test the effectiveness of contact lenses containing antimicrobial compounds, namely silver and furanone compounds, in controlling corneal inflammation caused by Pseudomonas aeruginosa. A guinea pig model of contact lens wear was developed for the study and it was observed that the ocular responses to contact lens wear in the guinea pig were similar to those seen in human eyes wearing contact lenses. Also, three different models for CLARE/IK were developed and tested in the guinea pig eye. The pathological features of CLARE/IK in the guinea pig were virtually identical to those observed in human eyes. Bacterial contamination of contact lenses was confirmed to be a major risk factor for the development of CLARE/IK. Contact lenses containing nano-particles of silver demonstrated very good antibacterial activity against Pseudomonas aeruginosa in-vitro. The silver lenses were able to control the development of CLARE/IK responses in one of the models for CLARE/IK. Silver lenses might be most effective if used to prevent the establishment of a biofilm of bacteria on a lens such as might occur during storage in a contact lens case. Contact lenses were coated with different concentrations of the furanone compounds by physical adsorption and demonstrated good antibacterial activity at higher concentrations. However these concentrations were cytotoxic in-vitro and lower concentrations of furanones did not possess adequate antibacterial activity to control CLARE/IK responses in-vivo. This thesis has successfully demonstrated that guinea pigs can be used to test the effects of extended wear of contact lenses and developed models to test the pathogenesis of adverse responses such as CLARE/IK. The CLARE/IK models developed could be used to further our understanding of the pathogenesis of these inflammatory conditions and explore the activity of other antimicrobials.

Thesis (M.S.)--New England College of Optometry, 2009. / Includes bibliographical references (p. 94-96).

M.Phil. (Optometry) / Please refer to full text to view abstract

Single Point Diamond Turning (SPDT) is a technology widely applied for the fabrication of contact lenses. One of the limiting factors in polymer machining is wear of the diamond tool due to electrostatic discharge resulting in poor surface quality of the machined products. The research work presented in this dissertation highlights the electrostatic properties of contact lenses during machining operations and the effects these properties have on the surface quality of the work piece materials. Two contact lens samples were experimented on, Definitive 74 (Silicone Hydrogel) and Tyro 97 (Rigid Gas Permeable). The electrostatic surface potentials (ESPs) were measured during turning operations using an electrostatic voltmeter and the surface roughness measurements were taken using a surface profilometer. Response Surface Methodology (RSM) techniques were employed to create predictive models for both surface roughness and ESPs with respect to the cutting speed, feed rate and depth of cut. Predictive surface roughness models were successfully generated for both materials and the cutting speed and feed rate were identified as the parameters with most effect on surface roughness. In addition, an electrostatic model was successfully generated for the Definitive 74 contact lens material which cited the cutting speed and feed rate as the most effective parameters on the material’s electrostatic behaviour. However, no relationship was evident between the machining parameters and electrostatic behaviour of Tyro 97.

No description available.

No description available.

The pursuit of optimizing soft contact lens performance has been extensive, given that approximately over 140 million contact lens wearers globally seek the convenience and visual acuity they offer. However, a persistent challenge is the prevalence of ocular dryness and discomfort experienced by almost half of these wearers, particularly towards the end of the day. The occurrence of these symptoms is primarily attributed to diminished compatibility between the contact lens and the ocular surface leading to contact lens discontinuation. A promising method to improve overall contact lens properties is to incorporate novel monomers with unique functionalities during the initial manufacturing stage. Monomers bearing ionic functional groups have been extensively explored to improve bulk and surface properties of biomaterials. The incorporation of cationic and zwitterionic monomers in the fabrication of hydrogel materials has shown to have anti-fouling and anti-bacterial properties and improved surface wetting. In this work, a series of novel materials using cationic and zwitterionic monomers were prepared and their impact on bulk and surface properties of contact lens materials were assessed. Furthermore, the impact of a novel hydrophilic silicone-based monomer bearing zwitterionic phosphocholine was investigated for water-based extraction, physiochemical and structural stability in candidate contact lens materials. In Chapter 2, a library of eleven positively charged (cationic) and electrically neutral with both positive and negative charges (zwitterionic) functional methacrylate ester monomers was produced through the reaction of 2-(dimethylamino) ethyl methacrylate (DMAEMA) with different alkyl halides. The Menshutkin reaction was carried out with a high level of success, resulting in moderate to high yields of the desired monomers. The monomers were purified and characterized using analytical techniques, including 1H-NMR (proton nuclear magnetic resonance), 13C-NMR (carbon-13 nuclear magnetic resonance), LCMS (liquid chromatography-mass spectrometry), and XRD (X-ray diffraction). Six monomers were chosen based on controlled end group hydrophilicity and chain length to investigate the relationship between chemical structure and overall performance in hydrogel and silicone hydrogel systems. In Chapters 3 and 4, model hydrogel and silicone hydrogel systems via UV free-radical polymerization at increasing input concentrations (10 and 20 wt%) were manufactured using the monomers and HEMA (hydrogel) or HEMA + SIGMA (silicone hydrogel). The novel materials demonstrated an increase in bulk equilibrium water content, reduced contact angle and nonspecific lysozyme and albumin adsorption, while maintaining optical transparency at higher than 90%. In vitro studies demonstrated the ionically charged hydrogel materials did not show any toxicity to human corneal epithelial cells. In Chapter 5, a super hydrophilic silicone-based SIGMAPC monomer was synthesized using the siloxane functional monomer (SIGMA) as the main building block. The introduction of the novel hydrophilic SIGMAPC monomer led to significant improvements in the silicone materials. The hydrogels showed increased water content and reduced water contact angles, indicating their superior hydrophilicity. Moreover, the rate of dehydration was decreased, and the nonspecific deposition of lysozyme and albumin was minimized. Importantly, the optical transparency of the hydrogel silicone remained above 90%. Based on these findings, it can be concluded that the siloxane-based monomer bearing a zwitterionic phosphocholine has great potential for applications in contact lenses, given its desirable properties and biocompatibility. Furthermore, in Chapter 6, 31P-NMR and weight extraction analysis showed model contact lens materials made with SIGMAPC were effectively extracted in aqueous media at elevated temperature. Candidate materials showed good dimensional and optical stability pre- and post-thermal sterilization and over 6-month storage period. / Thesis / Doctor of Philosophy (PhD)