|Author:||Chan, Ka Yin|
|Title:||Surface pigments on cosmetic contact lenses and implications on safe contact lens wear|
|Advisors:||Cho, Pauline (SO)|
Contact lenses -- Care and hygiene.
Hong Kong Polytechnic University -- Dissertations
|Department:||School of Optometry|
|Pages:||xx, 205 pages : illustrations|
|Abstract:||Background: The use of cosmetic contact lenses (CCL) has become increasingly popular especially in Asian countries such as Korea, Taiwan,Singapore and China.The public can easily purchase CCL online, at cabinet stores, flea markets, department stores, and accessories stores. CCL not prescribed and dispensed from optometric practices are just commodities to the salespersons who have no proper training in contact lens care and handling.Lack of training poses a threat to wearers who are not provided with any eye examination, aftercare services, or advice on proper lens usage and care. The quality of these CCL is also an issue as there is a lack of information on the manufacturer, the pigments used, manufacturing process, and the colour printing process. With huge demand for CCL in the market and lack of regulations of the sale of CCL, there is a need to review the safety of CCL. To date, research on CCL is scarce. This is probably due to the relatively low popularity of CCL, particularly in Caucasian countries. It was not until recent years that CCL regained attention due to increasing popularity in Asian countries and reports of microbial keratitis cases related to CCL. There was therefore a need to investigate the characteristics of CCL, particularly surface pigment CCL, and their implications on safe CCL wear. Objectives: The objectives of this PhD study were to: 1. develop a method to determine the location and permanency of pigments on CCL 2.investigate the effect of surface pigments of CCL on microbial adherence 3. investigate cytotoxic effect of surface pigment of CCL on porcine corneal epithelial cells using the new porcine eye model(PEM) 4.investigate the effect of surface pigments of CCL on protein deposition Methods: Experiment 1: The permanency of pigments of five brands of CCL was tested using a cotton bud rub-off test.Each lens was removed from its blister pack and placed on the cleaned surface of an electronic scale to allow monitoring of the force applied when each lens was rubbed to ensure consistency of force applied (applied force between 110 230g) for all lenses.Any pigment coming off the lens surface was determined by examining the tip of the cotton bud for pigment transfer after every rub. The procedures were repeated on both front and back surface. Experiment 2: Fifteen brands of new CCL (five lenses of each brand) were challenged with Pseudomonas aeruginosa ATCC 9027. Three brands of lenses and their clear counterparts were also challenged with Staphylococcus aureus ATCC 6538 and Serratia marcescens ATCC 13880.Lenses were incubated in bacterial suspension immediately after they were removed from the blister packs or storage vials. After 24 hours,the lenses were removed aseptically and rinsed gently with phosphate buffered saline to remove loosely attached micro-organisms and the viable organisms adhered to the lenses were enumerated using an automated colony counter after plating. Experiment 3: In order to test the cytotoxic effects of CCL in an ex vivo model,improvements were needed to the existing porcine eye model. These modifications were required because the current model only allows two porcine eyes set up each time and there was no strict control of the surrounding temperature or humidity. A total of 57 porcine eyes were used and they were mounted on four test PEM with blinking and lacrimation simulation. The nictitating membrane of the porcine eyes was held by a movable arm connecting to a motor to simulate blinking. An infusion wing was set right above the cornea so that Dulbecco's phosphate buffered saline (DPBS) could be applied to the superior limbal region regularly to simulate lacrimation. Viability of the corneal epithelial cells was assessed with 0.4% trypan blue solutions three hours after the commencement of the experiment. Two controls were set up: control A was to assess cell viability immediately without any treatment and control B was to assess cell viability on PEM without blinking and lacrimation simulation after three hours.Back surface pigment CCL and the clear contact lens clear counterparts were pre-soaked in different multipurpose solutions (MPS) and hydrogen peroxide system for 24 hours. The CCL were then placed on the porcine eyes on PEM with blinking and lacrimation simulation. Cell viability was assessed after three hours of experiment using Annexin V-FITC/7-AAD kit. Experiment 4: Ten young adults aged 18-35 years old were recruited. Subjects were required to wear the contact lenses (two brands of CCL and one clear contact lenses of the same lens material) for eight to ten hours. At the end of a day's wear, the subjects returned to the clinic and the contact lenses were removed and collected for protein quantification.|
Results: Experiment 1: Only one brand of CCLs was found to have no pigment coming off after repeated rubs with a wetted cotton bud. The other CCL all had pigment transferred to the cotton bud after two rubs (Range: 1-7).Experiment 2:Surface pigment CCL showed significantly higher amounts of microbial colonization than their clear counterparts for all bacterial species tested (p<0.028). No significant differences in the amount of microbial adherence were observed between the sandwich design CCL lenses and their clear counterparts for all strains of micro-organisms (p>0.402).Experiment 3: No significant difference was found in the number of dead cells between the four test PEMs in both central (p=0.53) and peripheral cornea (p=0.19). There were significantly more dead cells (central and periphery) in the test PEMs compared to control A (p<0.01) but significantly less when compared to control B (p<0.01). The results showed that all MPS showed no significant difference in the percentages of healthy cells between the CCL and clear contact lenses (p>0.05). The number of early necrotic,late necrotic and apoptotic cells between CCL and clear contact lenses in all tested solutions were also not significantly different (p>0.05). Experiment 4: The results showed no significant differences in protein deposition between sandwich CCL (Median: 583 [Range: 362 - 980]) or surface pigment CCL (Median: 600 [Range: 483 - 892]) and clear contact lens (Median: 639 [Range: 347 - 731]). Conclusions:The rub-off test provided an indirect and simple method to determine the pigment location of CCL. Our study showed that CCL with pigments printed on the surface resulted in significantly higher bacterial adhesion.However,using the improved PEM showed that the cytotoxic effects of leachates from surface pigments CCL were not significantly different compared to those of clear contact lenses after three hours of exposure.Protein deposition on CCL, either sandwiched or surface pigments, after one day of lens wear, was also not different from those on clear contact lenses worn by the same subject.
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