Contact lens success is primarily driven by comfort of the lens in eye. Over the years, many modifications have been made to the lens surface and bulk material to improve comfort of the lens, however 50% of contact lens wearers still report dry eye symptoms while wearing their lenses. Wettability of the lens material plays a large role in lens comfort, primarily due to its influence in tear film stability. In vitro wettability of contact lenses has typically been assessed by measuring the water contact angle on the lens surface. Currently there are three techniques to measure the in vitro wettability of contact lenses, the sessile drop technique, captive bubble technique, and the Wilhelmy balance method. To date, there is much published on assessing wettability using the sessile drop and captive bubble technique, however there is no data published looking at the in vitro wettability of hydrogel contact lenses measured by the Wilhelmy balance method. Accumulation and deposition of tear components on the lens surface can also affect lens performance, by altering the wettability of the lens surface and causing lens spoilage. The majority of in vitro studies looking at deposition of tear components on the lens surface dope the lenses in tear solutions for a set period of time. None of these studies have investigated the impact of exposing the lenses to tear solutions, then exposing them to the air and then back into the tear solution, which mimics the process during blinking. In Chapter 2, an evaluation of the influence of lens preparation on the wettability of contact lenses measured by the sessile drop technique was conducted. The wettability of 6 silicone hydrogel and one conventional lens material was assessed. Lenses were blot dried on either a microfiber cloth or lens paper for different drying periods and contact angles were measured using the sessile drop technique. There were large variations in results using the microfiber cloth after all drying periods, but there was little variation in results after lenses were blot dried on lens paper for approximately 20 seconds. Thus, it was determined that for future contact angle analysis using the sessile drop technique that lenses should be blot dried for roughly 20 seconds on lens paper. This method was used consistently for the rest of the experiments in which the sessile drop technique was used to measure contact angles. The remainder of Chapter 2 compared the contact angles of different lens materials measured by the sessile drop technique and Wilhelmy balance method. The wettability of five different silicone hydrogel lens materials was assessed directly out-of-blister and after a 48 hour soak in saline. There were significant differences in contact angles for the lens materials between the two techniques. There were also significant differences in contact angles directly out-of-blister and after the 48 hour soak. Results from this study suggested that different methods of measuring wettability can produce different results and that blister pack solutions can alter the wettability of lens materials. Chapter 3 measured the physical properties of blister pack solutions of silicone hydrogel lenses. The pH, osmolality, surface tension, and viscosity of the blister solutions for 9 silicone hydrogel lenses, 2 conventional lenses, and 2 saline solutions were measured. The osmolality of the blister solutions followed a trend, in that blister solutions manufactured by the same company had the same osmolality. Products produced by Johnson & Johnson had the highest osmolality. Blister solutions that contained additional wetting agents had higher viscosities compared to blister solutions without added wetting agents. The main conclusion from this study was that adding wetting agents to blister solutions could alter the physical properties of the blister solutions. The purpose of Chapter 4 was to measure the physical properties of the blister pack solutions of daily disposable lenses and to evaluate the wettability of the lens materials and substantivity of the blister solutions, using a method in which lenses were cycled through 5 minute soaks in saline to mimic blinking. Five daily disposable lens materials were evaluated, one of which was shipped in a blister solution with added surfactants and wetting agents. The wettability of the lenses was assessed using the sessile drop technique and Wilhelmy balance method. The lens with the modified blister solution had a lower surface tension and higher viscosity compared to all the other blister solutions. The same trend in osmolalties as those reported in Chapter 3, were found with blister solutions made by the same manufacturer having the same osmolality. The wettability varied across lens materials. Overall, the lens material with the added components to the blister solution had the lowest contact angle. Chapter 5 investigated the deposition of tear components onto the surface of conventional and silicone hydrogel lens materials and looked at the impact of this on changes in wettability. Three lens materials used in Chapter 4 were exposed to a saline solution, lysozyme solution, and a complex tear solution for 5 minutes, 1 hour, 4 hours, and 8 hours. The wettability was assessed after each time point using the sessile drop and Wilhelmy balance methods. There was little to no deposition on the lens materials that had the highest in vitro CAs in Chapter 4, exemplified by no change in wettability after being soaked in the lysozyme and complex tear solutions. There was deposition on the lens materials with the lowest CAs in Chapter 4, exemplified by a significant increase in wettability after being soaked in the lysozyme and complex tear solutions. Results indicate that there is some deposition onto one lens material, as shown by the change in wettability of the lens surface. These results were further used to validate a method used in Chapter 6. The experiment conducted in Chapter 6 was similar to the experiment in Chapter 5, except that the lenses were not soaked in the three solutions but rather exposed to the solutions in a “model blink cell”. The model blink cell moves lenses in and out of solution at a set time interval, in an attempt to mimic blinking. The interval was set so the lenses would be placed for 1 second in solution and 5 seconds exposed to the air. The same lens materials used in Chapter 5 were used in for this experiment. The lenses were exposed to a saline solution, lysozyme solution and complex tear solution for 5 minutes, 1 hour, 4 hours, and 8 hours. Much like in Chapter 5, deposition on the lens materials was determined by a change in the lens wettability. There were differences in the results of this chapter and that of Chapter 5, with deposition occurring on two of the lens materials rather than just one. This result indicates that the drying of the lens surface for 5 seconds out of solution has an effect on the deposition of tear components on certain lens materials. Thus, the model blink cell may be a useful tool for future deposition studies. Overall this thesis demonstrated that preparation of the lens material can cause variation in contact angles. Different methods of measuring in vitro wettability of contact lenses can produce different results and thus the method used to assess wettability should always be stated. The physical properties of blister pack solutions can change with added wetting agents and surfactants, and components from blister solutions can alter the initial wettability of contact lenses. In vitro deposition of proteins onto the lens surface can vary with techniques, and finally, deposition of tear components onto the surface of contact lenses can alter the lens wettability.

Contact lens success is primarily driven by comfort of the lens in eye. Over the years, many modifications have been made to the lens surface and bulk material to improve comfort of the lens, however 50% of contact lens wearers still report dry eye symptoms while wearing their lenses. Wettability of the lens material plays a large role in lens comfort, primarily due to its influence in tear film stability. In vitro wettability of contact lenses has typically been assessed by measuring the water contact angle on the lens surface. Currently there are three techniques to measure the in vitro wettability of contact lenses, the sessile drop technique, captive bubble technique, and the Wilhelmy balance method. To date, there is much published on assessing wettability using the sessile drop and captive bubble technique, however there is no data published looking at the in vitro wettability of hydrogel contact lenses measured by the Wilhelmy balance method. Accumulation and deposition of tear components on the lens surface can also affect lens performance, by altering the wettability of the lens surface and causing lens spoilage. The majority of in vitro studies looking at deposition of tear components on the lens surface dope the lenses in tear solutions for a set period of time. None of these studies have investigated the impact of exposing the lenses to tear solutions, then exposing them to the air and then back into the tear solution, which mimics the process during blinking. In Chapter 2, an evaluation of the influence of lens preparation on the wettability of contact lenses measured by the sessile drop technique was conducted. The wettability of 6 silicone hydrogel and one conventional lens material was assessed. Lenses were blot dried on either a microfiber cloth or lens paper for different drying periods and contact angles were measured using the sessile drop technique. There were large variations in results using the microfiber cloth after all drying periods, but there was little variation in results after lenses were blot dried on lens paper for approximately 20 seconds. Thus, it was determined that for future contact angle analysis using the sessile drop technique that lenses should be blot dried for roughly 20 seconds on lens paper. This method was used consistently for the rest of the experiments in which the sessile drop technique was used to measure contact angles. The remainder of Chapter 2 compared the contact angles of different lens materials measured by the sessile drop technique and Wilhelmy balance method. The wettability of five different silicone hydrogel lens materials was assessed directly out-of-blister and after a 48 hour soak in saline. There were significant differences in contact angles for the lens materials between the two techniques. There were also significant differences in contact angles directly out-of-blister and after the 48 hour soak. Results from this study suggested that different methods of measuring wettability can produce different results and that blister pack solutions can alter the wettability of lens materials. Chapter 3 measured the physical properties of blister pack solutions of silicone hydrogel lenses. The pH, osmolality, surface tension, and viscosity of the blister solutions for 9 silicone hydrogel lenses, 2 conventional lenses, and 2 saline solutions were measured. The osmolality of the blister solutions followed a trend, in that blister solutions manufactured by the same company had the same osmolality. Products produced by Johnson & Johnson had the highest osmolality. Blister solutions that contained additional wetting agents had higher viscosities compared to blister solutions without added wetting agents. The main conclusion from this study was that adding wetting agents to blister solutions could alter the physical properties of the blister solutions. The purpose of Chapter 4 was to measure the physical properties of the blister pack solutions of daily disposable lenses and to evaluate the wettability of the lens materials and substantivity of the blister solutions, using a method in which lenses were cycled through 5 minute soaks in saline to mimic blinking. Five daily disposable lens materials were evaluated, one of which was shipped in a blister solution with added surfactants and wetting agents. The wettability of the lenses was assessed using the sessile drop technique and Wilhelmy balance method. The lens with the modified blister solution had a lower surface tension and higher viscosity compared to all the other blister solutions. The same trend in osmolalties as those reported in Chapter 3, were found with blister solutions made by the same manufacturer having the same osmolality. The wettability varied across lens materials. Overall, the lens material with the added components to the blister solution had the lowest contact angle. Chapter 5 investigated the deposition of tear components onto the surface of conventional and silicone hydrogel lens materials and looked at the impact of this on changes in wettability. Three lens materials used in Chapter 4 were exposed to a saline solution, lysozyme solution, and a complex tear solution for 5 minutes, 1 hour, 4 hours, and 8 hours. The wettability was assessed after each time point using the sessile drop and Wilhelmy balance methods. There was little to no deposition on the lens materials that had the highest in vitro CAs in Chapter 4, exemplified by no change in wettability after being soaked in the lysozyme and complex tear solutions. There was deposition on the lens materials with the lowest CAs in Chapter 4, exemplified by a significant increase in wettability after being soaked in the lysozyme and complex tear solutions. Results indicate that there is some deposition onto one lens material, as shown by the change in wettability of the lens surface. These results were further used to validate a method used in Chapter 6. The experiment conducted in Chapter 6 was similar to the experiment in Chapter 5, except that the lenses were not soaked in the three solutions but rather exposed to the solutions in a “model blink cell”. The model blink cell moves lenses in and out of solution at a set time interval, in an attempt to mimic blinking. The interval was set so the lenses would be placed for 1 second in solution and 5 seconds exposed to the air. The same lens materials used in Chapter 5 were used in for this experiment. The lenses were exposed to a saline solution, lysozyme solution and complex tear solution for 5 minutes, 1 hour, 4 hours, and 8 hours. Much like in Chapter 5, deposition on the lens materials was determined by a change in the lens wettability. There were differences in the results of this chapter and that of Chapter 5, with deposition occurring on two of the lens materials rather than just one. This result indicates that the drying of the lens surface for 5 seconds out of solution has an effect on the deposition of tear components on certain lens materials. Thus, the model blink cell may be a useful tool for future deposition studies. Overall this thesis demonstrated that preparation of the lens material can cause variation in contact angles. Different methods of measuring in vitro wettability of contact lenses can produce different results and thus the method used to assess wettability should always be stated. The physical properties of blister pack solutions can change with added wetting agents and surfactants, and components from blister solutions can alter the initial wettability of contact lenses. In vitro deposition of proteins onto the lens surface can vary with techniques, and finally, deposition of tear components onto the surface of contact lenses can alter the lens wettability.

An analysis of the performance of simple refractive null compensators was done. Two types of correctors were studied--the Dall compensator and the Offner compensator. A framework was built for determining whether these simple null tests are adequate for a wide range of aspheric surfaces. Variables involved in determining a surface to be null tested are f-number, conic constant, and focal length. Examples are given on how to determine the best null test for several aspheric surfaces. Also of concern in the design of a null compensator was simplicity. Two elements were the maximum used for both compensators and all compensator surfaces were spherical.

No description available.

No abstract available. / Thesis (Ph.D.)-University of Natal, 1995.

AIM: The primary purpose of this thesis was to evaluate the pattern of changes to accommodation and phoria when pre-presbyopic individuals perform near work for 20 minutes with +2D lenses. In addition, the thesis also investigates the effect of the accommodative vergence cross-link (AV/A) and age on binocular adaptation to addition lenses. METHODS: Accommodation was measured using the PowerRefractor (Multichannel Systems, Germany) and phoria was measured using the modified Thorington Technique. Twenty four pre-presbyopic and emmetropic individuals (11 adults and 13 children) participated in the study. All participants fixated a near target at a distance of 33 cm for 20 minutes with +2D (lens condition) and without (no lens condition) +2D addition lenses. Binocular and monocular changes in accommodation and near phoria were measured at the outset and at 3, 6, 9, 15 and 20 minute intervals. RESULTS: Effect of +2D lenses on accommodation and phoria: The emmetropic adult participants exhibited lag of accommodation under the no lens condition (binocular: 0.51 ?? 0.12D; monocular: 0.64 ?? 0.15D) that were eliminated (under monocular viewing) and reversed (exceeded demand by 0.51 ?? 0.11 D under binocular viewing condition) with the addition of +2D lenses. The near phoria showed a significant increase towards exophoria by 6 ?? 0.56 ???D upon introduction of +2D lenses. Sustained near viewing with +2 D lenses resulted in significant reduction of the binocular focus alone (not monocular focus) after 3 minutes of binocular viewing (magnitude of reduction: 0.24D; P<0.01). The exophoria also showed a concomitant reduction after 3 minutes of fixation at the near task (Magnitude of reduction: 3.6 ?? 0.6 ???D; P<0.001). The magnitude and rate of vergence adaptation, determined using an exponential function, was found to be 4.6 ?? 0.21 ???D and 2.12 minutes respectively for the emmetropic adult participants. Effect of age on vergence adaptation: A pattern of significant reduction in phoria and binocular focus similar to the adult participants was observed in young children. Analysis of the vergence adaptation curves in the two age groups did not show any significant difference in both the magnitude as well as the rate of phoria adaptation within the age range tested (Magnitude of adaptation - Adults: 4.65 ???D; Children: 4.51 ???D; P > 0.05; Time constants -Adults: 2.12 minutes: Children: 1.53 minutes, P > 0.05). Effect of AV/A ratio on vergence adaptation: The stimulus (St-AV/A) and the response AV/A (R-AV/A) ratios were determined and the participants were divided into two groups (low and high AV/A ratio) under both the conditions. The result indicated that, under both testing conditions (stimulus and response AV/A), the individuals with higher AV/A ratios demonstrated greater magnitudes of vergence adaptation than those individuals with lower ratios (Magnitude of adaptation: Low St-AV/A = 4.12 ???D; Low R-AV/A= 4.25???D; High St-AV/A = 4.88 ???D; High R-AV/A = 4.65???D; P<0.05) CONCLUSIONS: Introduction of near addition lenses initiated an increase in exophoria and convergence driven accommodation. Vergence adaptation occurred after 3 minutes of binocular viewing thus reducing exophoria and convergence driven accommodation. The magnitude and completeness of phoria adaptation were seen to depend on an individuals AV/A ratio with greater magnitude and incomplete adaptation observed in participants with higher AV/A ratios. Age, within the limits of the study did not appear to influence phoria adaptation with near addition lenses.

Microbial keratitis is the most serious, and only potentially blinding complication of contact lens wear. To further understand and reduce the risk of this disease, incidence rates and risk factors have been estimated in numerous studies. Since these studies were conducted, new lens types have been introduced designed to reduce the risk of infection. It was hypothesised that the issues of contact lens related hypoxia and poor lens hygiene could be addressed by the introduction of silicone hydrogel and daily disposable lenses respectively. This thesis describes the incidence of and risk factors for contact lens related microbial keratitis in Australia and New Zealand. The incidence of infection was determined by capturing all cases of contact lens related presumed microbial keratitis in a 12-month surveillance study, and by estimating the number of lens wearers using a population-based phone survey. Characteristics of the cases and controls were compared to estimate risk factors. In Australia, rates of infection with daily and overnight wear of hydrogel lenses were similar to previously published reports (1.9 [95%CI]:1.8-2.0] and 19.5 [95%CI:14.6-29.5] per 10,000 wearers respectively). Compared to the incidence of infection with hydrogel lenses, silicone hydrogel lenses had a higher rate in daily wear (11.9 [95%CI: 10.0-14.6]), and a similar rate in extended wear (19.5 [95%CI:14.6-29.5]). Daily disposable lenses had a similar rate of infection to daily wear of hydrogel lenses (2.0 [95%CI:1.7-2.4]), but appeared to reduce the incidence of severe or vision loss keratitis (0.5 [95%CI: 0.5-0.6] and 0.0 [95%CI: 0.0-0.0] respectively). Conducting the study in New Zealand confirmed the increase in incidence for overnight use of lenses, irrespective of lens type. Comparison of the incidence rates in New Zealand and Australia show that the rates in the two countries are comparable, bar an unexplained lower rate of infection for extended wear of soft hydrogel lenses in New Zealand. Risk factors for infection were overnight use of lenses, from occasional overnight to extended wear use, poor lens case hygiene, smoking, high socio-economic status and less than 6 months experience in current lens type. Amongst daily wearers, Internet or mail order purchasing of lenses was also associated with a higher risk of infection. This study is unique in terms of the study design and sample size, and the wide scope of risk factors considered. The determination of these incidence rates of infection and identification of risk factors is of extreme value to lens wearers and lens care practitioners around the world, particularly as the strongest and most prevalent risk factors are modifiable.

AIMS 1. To establish the patient demographics, risk factors, causative organisms, levels of antibiotic resistance, clinical presentations and treatment patterns of keratitis at a tertiary referral hospital in Australia. 2. To establish any change in these factors over 5 years. 3. Establish the factors associated with poor outcomes. METHODS: A retrospective audit of all patients who had a corneal culture in 5 years was conducted. Patients' clinical information was gathered from medical records and smear, culture and antibiotic resistance results were gathered from the local microbiology database. Associations between risk factors for keratitis and patient variables were analysed statistically. Outcome of a patient's episode of keratitis was classified as poor using final criteria. Trends over time in variables were analysed using linear regression. RESULTS: Two hundred and fifty-three (253) corneal cultures of 231 patients were included. Sixty percent (60%) of patients were male and there was a bimodal distribution in the age of presentation. Common risk factors for keratitis were contact lens wear (22%), ocular surface disease (18%), ocular trauma (16%) and prior ocular surgery (11 %). Corneal cultures were positive in 65% of cases and Pseudomonas aeruginosa (27%), coagulase-negative staphylococci (13%), Staphylococcus aureus (12%) and fungi (7%) were recovered. There was significant variation in the monthly recovery of P. aeruginosa (p=0.04) and fungi (p=0.02) which were more frequent in summer months, while Streptococcus pneumonia (p=0.04) was more common in winter months. Antibiotic resistance of cultured bacteria to cephalothin increased significantly (2% to 12%; p=0.02). Final vision of 6/12 or better was found in 48% (100) of cases while a poor outcome was seen in 28% (58) of cases. Multivariate analysis showed that the relative risk of a patient having a poor outcome was 4.3x (confidence interval [Cl] 2.0 to 9.5) if they had severe keratitis, 4.1 x (Cl 1.8 to 9.5) if they had keratitis related to ocular surface disease and 3.8x (Cl 1.8 to 8.3) if they were over 50 years old. CONCLUSIONS 1. In this series the most common risk factor for keratitis was contact lens wear and the most commonly isolated organism was P. aeruginosa which had seasonal variation in rate of recovery. 2. Keratitis related to contact lens wear became more frequent while keratitis related to prior ocular surgery became less frequent. 3. A poor outcome is more likely in patients with severe keratitis, keratitis related to prior ocular surface disease or older age.

Microbial keratitis is the most serious, and only potentially blinding complication of contact lens wear. To further understand and reduce the risk of this disease, incidence rates and risk factors have been estimated in numerous studies. Since these studies were conducted, new lens types have been introduced designed to reduce the risk of infection. It was hypothesised that the issues of contact lens related hypoxia and poor lens hygiene could be addressed by the introduction of silicone hydrogel and daily disposable lenses respectively. This thesis describes the incidence of and risk factors for contact lens related microbial keratitis in Australia and New Zealand. The incidence of infection was determined by capturing all cases of contact lens related presumed microbial keratitis in a 12-month surveillance study, and by estimating the number of lens wearers using a population-based phone survey. Characteristics of the cases and controls were compared to estimate risk factors. In Australia, rates of infection with daily and overnight wear of hydrogel lenses were similar to previously published reports (1.9 [95%CI]:1.8-2.0] and 19.5 [95%CI:14.6-29.5] per 10,000 wearers respectively). Compared to the incidence of infection with hydrogel lenses, silicone hydrogel lenses had a higher rate in daily wear (11.9 [95%CI: 10.0-14.6]), and a similar rate in extended wear (19.5 [95%CI:14.6-29.5]). Daily disposable lenses had a similar rate of infection to daily wear of hydrogel lenses (2.0 [95%CI:1.7-2.4]), but appeared to reduce the incidence of severe or vision loss keratitis (0.5 [95%CI: 0.5-0.6] and 0.0 [95%CI: 0.0-0.0] respectively). Conducting the study in New Zealand confirmed the increase in incidence for overnight use of lenses, irrespective of lens type. Comparison of the incidence rates in New Zealand and Australia show that the rates in the two countries are comparable, bar an unexplained lower rate of infection for extended wear of soft hydrogel lenses in New Zealand. Risk factors for infection were overnight use of lenses, from occasional overnight to extended wear use, poor lens case hygiene, smoking, high socio-economic status and less than 6 months experience in current lens type. Amongst daily wearers, Internet or mail order purchasing of lenses was also associated with a higher risk of infection. This study is unique in terms of the study design and sample size, and the wide scope of risk factors considered. The determination of these incidence rates of infection and identification of risk factors is of extreme value to lens wearers and lens care practitioners around the world, particularly as the strongest and most prevalent risk factors are modifiable.

Thesis (Ph.D.)--Tufts University, 1992. / Submitted to the Dept. of Electrical Engineering and Electro-Optics Technology Center. Adviser: Robert Gonsalves. Includes bibliographical references (leaves 195-206). Access restricted to members of the Tufts University community. Also available via the World Wide Web;