The CLAO journal : official publication of the Contact Lens Association of Ophthalmologists, Inc最新文献

Purpose: The purpose of this paper is to review the literature concerning the methods used to evaluate contact lens care solutions against Acanthamoeba. Acanthamoeba keratitis is a potential threat, with 85% of the cases being reported in contact lens wearers.

Methods: Several studies from the published literature that evaluated contact lens disinfectants were reviewed. The variables included test organism, strain and morphology, growth conditions, inoculum preparation, inoculation method, test solutions and concentration, contact time, neutralization, recovery, quantitation method, and viability determination of survivors. The methods used to test Acanthamoeba against the disinfectants were compared and contrasted.

Results: After a thorough review of methods used to test Acanthamoeba, it was found that there is great variability in the methods used to evaluate contact lens disinfectants. The majority of the studies used A.castellanii and A.polyphaga cysts grown axenically in PYG medium containing cations at about 30 degrees C and the inoculum contained about 1.0 x 10(5) cells/mL. Inactivation media or centrifugation of cells was used to neutralize test samples. Quantitation was performed in most studies and viability was checked in all studies. The disinfectants tested most often were PHMB, hydrogen peroxide, thimerosal, and chlorhexidine.

Conclusions: After reviewing the studies presented here it can be concluded that an effective method for testing Acanthamoeba against contact lens disinfectants would include A.castellanii or A.polyphaga grown axenically in PYG containing cations and a concentration of organisms high enough to adequately measure kill, a neutralization step, recovery and quantitation of organisms followed by a viability check of survivors.

Purpose: To describe the clinical and optical problems encountered in contact lens fitting following refractive surgery for high myopia.

Methods: Following refractive surgery for high myopia (greater than -10.00 D) we corrected residual refractive errors with contact lenses in the four eyes of two patients. The first patient had undergone bilateral laser in situ keratomileusis (LASIK),with two subsequent LASIK retreatments in the left eye. Ten months later she was fit with rigid gas permeable (RGP) lenses in both eyes. The second patient had undergone a clear lens extraction in the right eye and radial keratotomy followed by photorefractive keratectomy(PRK) in the left eye. She was fit with toric soft lenses six years postoperatively.

Results: Final visual acuity obtained with contact lenses was 20/25-20/20 in all eyes. The first patient required significant minus lens power compensation. Furthermore, the RGP lens in the left eye was slightly decentered due to corneal irregularity induced by LASIK. The second patient had regular corneal surfaces and was successfully fit with daily wear toric soft lenses despite the 2.75 D of residual astigmatism in the left eye.

Conclusions: Following refractive surgery for high myopia a proportion of patients will remain undercorrected. In these patients the alterations in corneal architecture that ensue make contact lens fitting more challenging. Patients with regular astigmatism may be fitted successfully with toric soft lenses. Patients with corneal irregularities should be fit with RGP lenses.

Purpose: Assessment of the characteristics of the myopic patient population applying for refractive surgery in order to determine the potential market for myopic refractive surgery.

Methods: Records of consecutive patients who responded to an advertisement for refractive surgery to correct myopia were evaluated retrospectively with regards to patient demographics and the amount and distribution of the refractive error. Data were compared to that available from population-based statistics for distribution of myopia in the general population. For statistical analysis, one sample Student's t-test and two tailed Student's t-test were utilized.

Results: Two hundred fifty seven patients (140 women and 117 men) responded to an advertisement for refractive surgery during the six month period between January and June 1998. Mean spherical equivalent (SEQ) of the patient population was -4.59+/-2.54 D (min;-0.25 D, max;-15.75 D) right eye (OD) and -4.62+/-2.82 D (min;-0.25 D, max;-15.25 D) left eye (OS). Among the patients who had myopia with an astigmatism of at most 1.00 D (n=165), the distribution of refractive error was statistically significantly different from that obtained from population-based statistics, such that, although most of the myopic population (40%) had an SEQ of -1.00 to -2.25 D, the majority of our patients (54.8%) who applied for myopic refractive surgery had an SEQ of -2.50 to -5.00 D. Another striking difference was that, although patients with an SEQ more than -6.00 D were a minority(2%) in the population study, in our study group, they comprised 16.7% of the patients seeking refractive correction. The difference between the SEQ of the right and left eyes ranged from 0.00 D to 13.0 D (mean, 0.89+/-1.5 D), 47.1 % having a difference of at most +/-0.5 D between the two eyes. The mean cylindrical error in the patient population was 0.69+/-0.93 D (min: 0, max: -4.5) OD and 0.69+/-0.96 D (min: 0, max: -4.5) OS. There were no statistically significant differences between the distribution of SEQ or cylindrical refractive error between males and females.

Conclusion: Although a population-based study reported that most of the myopic population (40%) had an SEQ of -1.00 to -2.25 D, the majority of our patients (54.8%) who applied for myopic refractive surgery had an SEQ of -2.50 to -5.00 D. On the other hand, while patients with an SEQ of -6.00 D and more constituted only about 2% of the general population, they accounted for 16.7% of our study population. Therefore, the refractive characteristics of the patient population applying for myopic refractive surgery may not necessarily parallel that of general population-based statistics. In order to establish a more effective refractive surgery practice, it is feasible to perform local studies and reevaluate the requirements of your practice accordingly.

Purpose: We conducted a cross-sectional survey to determine the prevalence, socio-demographic patterns, and characteristics of contact lens use in an electoral community in Singapore.

Methods: One thousand eight hundred fifteen persons aged between 12-55 years from 768 households were surveyed using a standardized pre-tested questionnaire.

Results: The percentage of contact lens wearers in the survey populations was 9.0%. Forty-two percent of surveyed individuals were myopes, 21.8% of whom wore contact lenses. Contact lens wearers tended to be young Chinese females with higher level education and incomes. Most wore monthly disposable or daily wear soft contact lenses. Convenience and cosmesis were the main reasons cited for contact lens wear. Optometrists, who prescribed the bulk of contact lenses, were also the most influential in determining consumers' choice of lenses.

Conclusion: Information gathered in this population-based survey may be used to facilitate national eye-care planning and provide a baseline for comparison with rates of lens wear found in other countries and in future surveys.

Purpose: To investigate the efficacy of a new large permanent wear soft contact lens in the management of leaking blebs following trabeculectomy.

Methods: Twenty-four patients with leakage from a trabeculectomy bleb, both fornix based and limbal based, with and without mitomycin adjuvant, were treated with a 78% water content soft contact lens of 17.5 mm diameter, fit according to each patient's keratometry readings.

Results: The leakage from a conjunctival trabeculectomy bleb was successfully treated in 22 out of 24 patients.

Conclusions: The 17.5 mm 78% water content permanent wear soft contact lens is a preferred method of management of leaking blebs when specifically tailored to the patient's corneal curvature.

Purpose: To assess the chronic effects of rigid gas-permeable (RGP) contact lenses on corneal swelling and glucose-lactate metabolism in the rabbit cornea during 1 month of continuous extended wear and to establish the relationship between these effects and the oxygen transmissibility (Dk/L) of the test lens polymer.

Methods: Four RGP lenses of varying Dk/L were tested in 8 rabbits per test group (left eyes served as controls). After 7 days and 1 month extended wear, the concentrations of lactate and glucose in the corneal epithelium, stroma and aqueous humor were determined by enzyme assay; and epithelial and stromal ATP concentrations were separately measured by bioluminescence techniques. Corneal thickness was measured at a standard morning time by ultrasonic pachymetry before and after 1, 7, 15 days and 1 month extended wear.

Results: After 7 days and 1 month extended wear, generalized decreases were found in aqueous humor lactate levels for all test lenses, while concomitant increased aqueous glucose concentrations were observed. Total epithelial lactate levels correlated inversely with decreasing Dk/L levels for lower oxygen transmissible lenses (R = 0.951, P = 0.0051); and remained unchanged after extended wear of the hyper-oxygen transmissible Dk/L 125 test lens. By contrast, stromal lactate levels consistently decreased at all time points measured forextended wear of all test lenses. As expected, both epithelial and stromal ATP concentrations simultaneously decreased in extended wear. Overnight corneal swelling values after 24 hours wear of Dk/L = 27, 43, 70 and 125 test lenses were increased by 9.8, 7.1, 5.5, and 5.2% while persistent (residual) stromal swelling after one month extended wear was 16.8, 10.1, 8.6, and 5.6% respectively, in excess of baseline values.

Conclusions: Chronic RGP contact-lens induced hypoxia is associated with altered glucose-lactate metabolism in the cornea and aqueous humor with excess production of increased levels of lactate in the epithelium for lower Dk/L test lenses, but decreased lactate concentration in the stroma and aqueous humor. Extended wear of the hyper-oxygen transmissible test lens (Dk/L = 125) however, produced no increase in epithelial lactate levels. Expected lens-induced decreases in epithelial and stromal ATP were not dependent on lens-oxygen transmissibility. Despite the persistence of lower than normal stromal levels of lactate during 1 month of extended wear for all test lenses, residual corneal swelling values remained consistently elevated above baseline values. Taken together, these data establish that increased stromal lactate accumulation cannot account for persistent stromal edema in chronic extended wear of RGP lenses; and that this effect appears to be independent of lens-oxygen transmissibility and may thus represent the prolonged mechanical effect of lens wear itself.

Purpose: To describe two cases of de novo development of corneal guttae and Fuchs' dystrophy in donor tissue following penetrating keratoplasty (PK) for unrelated conditions.

Methods: Two patients underwent PK for keratoconus and a disciform scar secondary to herpes simplex virus. They were followed clinically for a period of 16 and 11 years, respectively. Specular microscopy was used in one patient.

Results: Corneal guttae were first noted 10 years and 4 years following transplantation in the first and second patient, respectively. In both cases, the corneal guttae gradually increased in number, involving the central and temporal portions of the corneal graft There were no corneal guttae present in the host corneal rim or contralateral cornea of either patient.

Conclusions: These cases provide evidence to suggest that some corneas may be genetically predetermined to develop corneal guttae and Fuchs' dystrophy many years before any changes can be clinically detected.

Purpose: To present a case of anterior scarring in an epikeratophakia lenticule and its partially successful treatment with the excimer laser.

Methods: Excimer laser phototherapeutic keratectomy (PTK) was used to reduce corneal scarring in an epikeratophakia lenticule.

Results: Visual acuity improved after two sessions of PTK.

Conclusions: PTK is an alternative to epikeratophakia lenticule removal.

Purpose: To establish a novel and objective screening method for evaluating the cleaning efficacy of contact lens care solutions for removal of protein deposits on single rigid gas permeable (RGP) lenses.

Methods: New and unworn RGP lenses containing no nitrogen atoms were incubated in a standard tear protein test solution. Protein deposition on lenses was determined by X-ray photoelectron spectroscopy (XPS) before and after standardized cleaning with commercially available care solutions (daily cleaners A, B) and a wetting/soaking solution or with 0.1w/v% sodium dodecyl sulfate (SDS) as a control. Cleaning efficacy was calculated based on the percentage of nitrogen atoms present in the total elements of the measured XPS scan spectrum.

Results: Nitrogen atoms originating from residual protein deposits on RGP lenses after cleaning were determined by XPS. The cleaning efficacy of the wetting/soaking solution was lower (74%) than that of daily cleaners A and B (95%) or SDS (96%) controls.

Conclusions: XPS determination of residual protein deposits is a novel and direct evaluation method for determining the cleaning efficacy of RGP lens care solutions for single lenses.