PubMed · 1027819
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M D Sarver. 1976. The visual Rx.. https://pubmed.ncbi.nlm.nih.gov/1027819/
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BACKGROUND: International Organization for Standardization (ISO) document ISO 9913-1 details procedures for oxygen permeability coefficient (Dk) measurement of hydrogel contact lens materials up to 100 barrer. A draft ISO document 9913-2 describing the coulometric technique states that the recommended procedures are suitable for nonhydrogel materials. New generation hydrogel lens materials exceed 100 barrer, which is outside the scope of both documents. METHODS: A range of rigid gas-permeable materials from Dr. W. Benjamin's standard repository was used as a baseline to assess the accuracy of the polarographic and the coulometric methods. We also measured the permeability of a new generation hydrogel, lotrafilcon A, to explore the suitability of the polarographic and coulometric techniques for high-Dk hydrogel lenses. We modified equipment for both methods that incorporate several improvements including front surface masking to eliminate "edge effect." RESULTS: The coulometric technique provided results similar to those previously reported for the standard rigid gas-permeable materials and yielded relative standard errors typically <10%. The polarographic technique provided results similar to the accepted values for the standard rigid gas-permeable materials Dk <70 barrer only after the edge effect correction algorithm was applied. The polarographic results showed poor precision and significant, systematic differences from accepted values for the rigid gas-permeables with Dk > 70 barrer. CONCLUSIONS: The coulometric method is preferable for the measurement of contact lens materials with permeability >70 barrer. The coulometric method was successfully modified to include hydrogels.
The clinical effects of a patient-operated system of microwave disinfection for soft contact lenses were assessed in a prospective pilot trial involving 103 patients who were drawn from five optometric practices. Fifty-six subjects used the test system for 1 month, and 13 subjects continued use for a total of 3 months. Both test and control subjects were examined for clinical signs using slitlamp tests. After 1 month, the incidence of all signs reported in the microwave group was not significantly greater than in the control group (p = 0.267), and the same was true after 3 months (p = 0.214). There was a significantly greater incidence of edema in the 1-month test group and of staining in the control group. UV spectroscopic examination of worn lenses from test subjects exhibiting significant signs did not show a higher level of deposition than on lenses worn by control subjects (p = 0.397).
Ten brands of hydrogel contact lenses were selected from five of the six British Approved Name lens classification groups to test in vitro the effects of repeated heat disinfection by means of microwave irradiation. Each lens type was tested over a number of cycles corresponding to its scheduled number of wearing days. The total diameter and back vertex power of all 80 test and 12 control lenses were measured at the end of their relevant cycling period. The back optic zone radius, center thickness, and water content were measured for 40 test and 8 control lenses. No clinically significant change was found in any of the 10 brands tested. Statistically significant changes were found in the back optic zone radius of the Frequency 55 group and water content of the Precision UV group. Some discoloration was noted in Ciba Visitint lenses.