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.

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.

[Survey of severe contact lens-associated microbial keratitis in Japan].

PURPOSE: To understand the current state of severe contact lens (CL)-associated microbial keratitis in Japan. METHOD: The survey was conducted by the Japan Contact Lens Society and the Japanese Association for Ocular Infection in 224 facilities from April 2007 to March 2009. Patients who were diagnosed with CL-associated microbial keratitis and hospitalized for treatment were enrolled. Clinical characteristics of the keratitis, microbiologic findings and the status of CL hygiene were studied. RESULTS: A total of 350 patients were investigated, with an average age of 28.0 (9-90) years. Acanthamoeba was identified in 85 (24.3%) corneal specimens and Pseudomonus aeruginosa in 70 (20.0%) cases. One hundred ninety six (56.0%) patients were frequent replacement soft CL users. Extended wearing of daily-use CLs was found in 77 (22.0%) patients. Only 67 cases maintained good CL hygiene by daily rubbing-washing and the poor CL care situation was reviewed. CONCLUSION: The most frequently detected pathogenic microorganism was Acanthamoeba, followed by Pseudomonus aeruginosa. Our survey showed the importance of keeping good CL hygiene by proper lens care, and improvement of CL-related social regulations is urgently needed.

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 x 10). 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 x 10). 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.

Presence of Acanthamoeba and diversified bacterial flora in poorly maintained contact lens cases.

Acanthamoeba can cause visually destructive Acanthamoeba keratitis (AK) in contact lens (CL) users. The purpose of this study was to determine whether Acanthamoeba was present in the CL cases of CL wearers and to develop techniques to prevent the contaminations. To accomplish this, 512 CL case samples were collected from 305 healthy CL wearers. Using real-time PCR, Acanthamoeba DNA was detected in 19.1% of CL cases, however their presence was not directly associated with poor CL case care. Instead, the presence of Acanthamoeba DNA was associated with significant levels of many different bacterial species. When the CL cases underwent metagenomic analysis, the most abundant bacterial orders were Enterobacteriales followed by Burkholderiales, Pseudomonadales, and Flavobacteriales. The presence of Acanthamoeba was characterized by Propionibacterium acnes and Rothia aeria and was also associated with an increase in the α diversity. Collectively, Acanthamoeba contamination occurs when a diversified bacterial flora is present in CL cases. This can effectively be prevented by careful and thorough CL case care.

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 > or =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.

Evaluation of povidone-iodine as a disinfectant solution for contact lenses: antimicrobial activity and cytotoxicity for corneal epithelial cells.

Povidone-iodine (PVP-I) possesses broad-spectrum antimicrobial activity and is used clinically as a disinfectant. We evaluated the disinfectant properties and safety of PVP-I for use as a contact lens solution. The concentrations of PVP-I required to reduce the number of Staphylococcus aureus or Candida albicans by 3 log units were lower than were those of hydrogen peroxide, polyhexamethylene biguanide (PHMB), and benzalkonium chloride (BAK). The cytotoxicity of PVP-I for cultured human corneal epithelial (HCE) cells was less than that of the other three agents. The safety margin for PVP-I was thus greatest among the tested compounds. PVP-I appears suited for use as a contact lens disinfectant.

[Clinical interpretation of the subjective complaint of dryness in contact lens wearers].

PURPOSE: Patients wearing contact lenses who have the feeling of dryness without any objective symptoms of dry eye are sometimes seen in clinics. The purpose of this study was to determine if there was a difference in the clinical signs, personality, and mental condition between a group of contact-lens wearers with no symptoms and a group of contact-lens wearers with subjective symptoms of the feeling of dryness. SUBJECTS AND METHODS: Eighty-two patients who had no trouble with wearing soft contact lenses (SCL) were employed in this study. The patients were asked to fill out a questionnaire and Yatabe Guilford Personality test (Y-G test), and the height of tear meniscus and fluorescein staining were measured. RESULTS: Fifty-three patients (65%) complained of a feeling of dryness. There were no significant differences between the presence of the feeling of dryness and types of SCL, the height of tear meniscus, and the severity of fluorescein staining. On the other hand, there was a significant increase in the scores of positive, subjective, and impulsive personality trais on the Y-G test in the symptomatic group. CONCLUSION: For patients who have subjective symptoms of the feeling of dryness, careful observation of objective symptoms should be carried out, and their personality and mental condition should also be evaluated.

Bevel toric multicurve rigid gas-permeable lens for keratoconus.

PURPOSE: To evaluate the efficacy and safety of Twinbel bevel toric, a newly designed rigid gas-permeable (RGP) lens with a toric bevel curvature, for keratoconus. METHODS: A retrospective analysis of nine eyes of patients with keratoconus who had been wearing RGP contact lenses and were switched to Twinbel bevel toric at Yamaguchi University Hospital. Visual acuity and contrast sensitivity were measured under photopic conditions. Complaint symptoms were recorded as primary outcome measures at follow-up visits. Efficacy and safety were evaluated at 12 weeks after the switch to Twinbel bevel toric or later. RESULTS: Five eyes (55.6 %) showed an improvement in visual acuity with Twinbel bevel toric compared with the previous lens, whereas four eyes (44.4 %) maintained the same visual acuity as before. The mean best corrected visual acuity ± SD with Twinbel bevel toric was 0.01 ± 0.40 logMAR, significantly better (P = 0.044, paired Student's t test) than that (0.23 ± 0.51 logMAR) with the previous lens. Contrast sensitivity and subjective complaint scores did not differ significantly between Twinbel bevel toric and the previous lens. No serious complications of Twinbel bevel toric wear were observed. CONCLUSIONS: Fitting of Twinbel bevel toric improved visual acuity in eyes affected by keratoconus, thus providing a viable alternative for management of such eyes.

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.