Kiichi Ueda

Effects of ionic and surfactant agents on the antimicrobial activity of polyhexamethylene biguanide.

Objectives: Polyhexamethylene biguanide (PHMB) exhibits broad-spectrum antimicrobial activity and is included in multipurpose solutions for contact lenses as a disinfectant. Both cationic and hydrophobic features of PHMB are believed to support its association with microbial cell membranes through electrostatic and hydrophobic interactions. We now evaluated the effects of ionic and surfactant agents on the antimicrobial activity of PHMB. Methods: The antimicrobial activity of PHMB (1 ppm) against various bacteria and fungi was measured with the stand-alone procedure (ISO 14729, 2001). The effect of NaCl as an ionic isotonic agent on such an activity was determined in comparison with that of propylene glycol as a nonionic isotonic agent. The effect of the nonionic surfactant Poloxamer 407 (Px407) was similarly examined in the absence or presence of NaCl. Results: The antimicrobial activity of PHMB increased with time, being especially pronounced after 60 min. This activity was inhibited by NaCl in a concentration-dependent manner but was not affected by propylene glycol. Poloxamer 407 (4%) alone slightly increased the activity of PHMB toward Staphylococcus aureus and fungi. Although Px407 prevented the inhibitory effect of NaCl on PHMB activity against bacteria, it enhanced that observed with Candida albicans. Conclusions: The antimicrobial activity of PHMB was inhibited by adjustment of osmolality with the ionic agent NaCl but not by that with the nonionic agent propylene glycol. The surfactant Px407 exhibited complex effects on PHMB activity in the presence of NaCl. These findings indicate that the electrostatic interaction with the cell membrane is a dominant factor in the antimicrobial activity of PHMB.

Reversibility of effects of orthokeratology on visual acuity, refractive error, corneal topography, and contrast sensitivity.

Objectives. To investigate the changes in corneal shape and optical performance during and after discontinuation of overnight orthokeratology for correction of myopia. Methods. Both eyes of 15 subjects were fitted with overnight reverse-geometry orthokeratology lenses, which were then worn for >4 hr overnight for 52 weeks. Subjects were free of ocular disease and had a corrected visual acuity of ≥1.0. Refractive correction, uncorrected visual acuity, corneal topography, and contrast sensitivity (at 4 spatial frequencies) were measured under photopic conditions. Results. Refractive error (spherical equivalent) and contrast sensitivity were decreased, whereas uncorrected visual acuity, the surface asymmetry index, and the surface regularity index were increased, 1 week after the onset of overnight orthokeratology and remained so during the 52 weeks of treatment. These parameters had largely returned to baseline values by 8 weeks after treatment discontinuation. Conclusions. Overnight orthokeratology improved uncorrected visual acuity and reduced refractive error but increased corneal irregularity and impaired contrast sensitivity. However, these changes in visual function and corneal shape were reversed after discontinuation of orthokeratology lens wear.

Effects of tonicity-adjusting and surfactant agents on the antimicrobial activity of alexidine.

Objectives: Alexidine is a bis-biguanide disinfectant with two cationic active sites and hydrophobic ethylhexyl end groups, both of which are believed to support its association with microbial cell membranes through electrostatic and hydrophobic interactions. We evaluated the effects of tonicity-adjusting and surfactant agents on the antimicrobial activity of alexidine to assess its suitability as a disinfectant in multipurpose solutions for contact lenses. Methods: The antimicrobial activity of alexidine (4.5 ppm) against various bacteria and fungi was measured with the stand-alone procedure (ISO 14729, 2001). The effect of NaCl as an ionic tonicity-adjusting agent on such activity was determined in comparison with that of propylene glycol as a nonionic tonicity-adjusting agent. The effect of the nonionic surfactant Poloxamer 407 (Px407) was similarly examined in the absence or presence of NaCl. Results: Alexidine showed robust antimicrobial activity, with no organisms surviving after 1 hr. Antifungal activity was inhibited by NaCl in a concentration-dependent manner, whereas neither antibacterial nor antifungal activity was affected by propylene glycol. The activity of alexidine was not affected by Px407 (4%) alone but was attenuated by the combination of NaCl and Px407 with all microorganisms tested. Conclusions: The antifungal activity of alexidine was inhibited by adjustment of osmolality with the ionic agent NaCl but not by that with the nonionic agent propylene glycol. The surfactant Px407 reduced antimicrobial activity only in the presence of NaCl. These findings indicate that electrostatic and hydrophobic interactions with the microbial cell membrane are a key factor in the antimicrobial activity of alexidine.

Contrast visual acuity with bifocal contact lenses.

Purpose. To compare the quality of vision of a bifocal rigid gas-permeable contact lens versus a bifocal soft contact lens in subjects with presbyopia. Methods. Sixteen healthy presbyopic subjects with no ocular disease but experienced with contact lens wear were enrolled in the study. Subjects randomly wore both types of bifocal lenses for 30 minutes with a washout period of 30 minutes each in a crossover manner. The primary outcome measure was the difference in contrast visual acuity. Distance and near contrast visual acuities with the two bifocal lens types were measured in different lighting environments and at multiple contrast levels. After the measurement, subjects were asked to rate their subjective vision by using the four categories with both lens types throughout the study. At the end of the study, subjects were also asked which of the two lens types they preferred. Results. Under photopic conditions, distance and near visual acuities decreased at the 25% and 10% contrast levels, respectively, in subjects wearing bifocal soft contact lenses (P<0.05). Under scotopic conditions, distance visual acuity decreased at the 5% contrast level with the bifocal rigid gas-permeable contact lenses (P<0.05). For subjective responses of clarity, there were no differences between lens types for distance vision (P>0.05), but bifocal rigid gas-permeable lenses were clearer than bifocal soft contact lenses for near vision (P<0.05). Conclusions. Bifocal rigid gas-permeable contact lenses showed better visual performance than bifocal soft contact lenses did.

Retrospective analysis of vision correction and lens tolerance in keratoconus patients prescribed a contact lens with dual aspherical curves.

Objectives: To determine whether Aphex KC, a newly designed rigid gas-permeable (RGP) contact lens with dual aspherical base curves, improves visual acuity and lens wear time in patients with keratoconus. Methods: We performed a retrospective analysis of a noncomparative case series of 29 eyes of 24 patients with keratoconus who were intolerant of spherical RGP contact lenses and were fitted with Aphex KC at Yamaguchi University Hospital. Visual acuity and lens wear time were recorded as primary outcome measures at follow-up visits. Six patients with a follow-up period of <1 year were excluded from data analysis. At the last follow-up visit, 86.2% of eyes (25 eyes of 20 patients) continued to wear Aphex KC. Results: Mean uncorrected visual acuity was 1.4 LogMAR (20/500 in Snellen notation) for the 29 eyes enrolled in the study. Mean best-corrected visual acuity was 0.1 LogMAR (20/25) with Aphex KC and 0.7 LogMAR (20/111) with glasses (P < 0.001). A total of 19 eyes (65.5%) had a best-corrected visual acuity of 0.2 LogMAR (20/29) or better with Aphex KC. The mean ± SD wear time was 12.6 ± 3.2 hr/day with Aphex KC and 0.4 ± 0.7 hr/day with a previously prescribed spherical RGP contact lens (P = 1 × 10−12). The numbers of eyes wearing Aphex KC or the previously prescribed RGP contact lens for >12 hr/day were 26 and 0, respectively (P = 1 × 10−12). No serious complications of Aphex KC wear were observed. Conclusions: Fitting of an Aphex KC lens improved visual acuity and increased lens wear time in keratoconus patients who were intolerant of a spherical RGP contact lens. Aphex KC thus provides a viable alternative for management of such patients.

The important points in the use of multipurpose solution and the possibility of a novel contact lens care system containing povidone iodine

Purpose: This study was aimed at clarifying the important points in the use of multipurpose solution(MPS) and to evaluate the disinfection efficacy of a Povidoneiodine(PVP-I) disinfecting system against clinical isolates. Method: Eighty-six MPS bottles, contact lens (CL) cases, seventy-three lenses and usage information of each sample were collected from asymptomatic SCL wearers. Viable bacterial numbers in these samples and bacterial species were determined and then contamination rates and associated risk factors were analysed. Furthermore, disinfection efficacywas evaluated for 6MPS(5 PHMB,1 PQ-1), 2 hydrogen peroxide(1 step) and a PVP-I(1 step) available in Japan against planktonic or biofilm forms of four bacterial strains thatweremost commonly isolated fromcare products used by seven patients who were suspected CL-related microbial keratitis. Results: Of the samples tested, 2% of solution, 26% of CL cases, 14% of stored solution in CL cases and 12% of lenses were contaminated with ocular pathogenic microorganisms. The most often contaminants were S.marcescens, P.fluorescens, Alcaligenes species, and coagulase-negative Staphylococci. Contamination rate of CL case was significantly high in the cases that MPS was used for over 1 month(p<0.05) or CL case was used for over 2 months(p<0.01). Meanwhile, all MPS did not show sufficient efficacy against planktonic Alcaligenes or biofilm forms of other tested bacteria, even after an exposure timeof 24 and8hours respectively. On the contrary, the PVP-I and hydrogen peroxide system demonstrated high efficacy regardless of bacteria species and forms. Conclusions: These results demonstrate that MPS and CL case might be contaminated by environmental bacteria. Based on this study, we highly recommend using up MPS for less than 1 month after opening, replacing CL case when a new MPS is opened and using more effective disinfectant solution, such as PVP-I.