Introduction to oxygen permeability test of contact lenses

Since the contact lens is directly attached to the surface of the cornea of ​​the human eye, the wearer pays particular attention to the choice of the lens material in selecting the contact lens. Due to the influence of advertising, many wearers often pursue one-sided lenses with high water content when purchasing contact lenses. The higher the water content, the better the lens quality. In fact, the oxygen permeability of the lens is an important indicator of the contact lens. The various discomforts of wearing contact lenses and the length of wearing time depend on the oxygen transmission of the lens, and the high water content and ultra-thin of the lens are now promoted. In order to improve the oxygen permeability of the lens.

For the detection of oxygen permeability of contact lenses , ISO has developed test standards for oxygen permeability testing of contact lenses: ISO 9913-2 is suitable for rigid lens materials and non -hydrogel flexible contact lenses ( rigid non-hydrogel flexible contact lens) materials), test the amount of oxygen flow (oxygen flux) --j, oxygen permeability (oxygen permeability) --Dk, oxygen permeability (oxygen transmissibility) --Dk / t, and sample thickness of 0. ( thickness) --t, general evaluation index lenses with oxygen permeability Dk values. The detection principle is shown in Figure 1. After the sample is loaded into the test chamber, the test chamber is divided into upper and lower parts. The upper chamber is filled with a test gas with a certain oxygen content. The carrier gas flows into the Coulomb sensor through the lower chamber. The pressure on both sides of the sample is equal, but the partial pressure of oxygen is different. Oxygen enters the carrier gas flow through the membrane under the concentration difference, and is sent to the Coulomb sensor. The Coulomb sensor accurately measures the amount of oxygen carried in the nitrogen flow, thereby calculating the material. Oxygen transmission rate. The oxygen permeability testing equipment needs to use the reference membrane for equipment calibration before the formal test, determine the calibration factor of the equipment, and use it in the calculation of the formal test. The standard ISO 9913-2 clearly states that the sample used for calibration is SRM 1470 , which is identical to the reference film used in the film test standard ASTM D 3985 .

 

Figure 1. Test schematic

Note: 1. Air source; 2. Carrier gas source; 3. Gas dryer; 4. Humidity regulator; 5. Temperature controller; 6. Coulomb sensor; 7. Voltage recording device

 

At present , the TOY-C2 Oxygen Permeator manufactured by Jinan Languang Electromechanical Technology Co., Ltd. ( labthink ) is excellent in meeting the oxygen permeability test of contact lenses. The instrument has an independent temperature control device to achieve 5 °C -95 °C. Temperature control. In addition, relying on the strong support of the Labthink Barrier Lab can provide more detailed testing and consulting services for contact lens companies.

The test process mainly has the following steps: purging the system zero point, introducing oxygen flow into the test upper chamber, the sensor output value is stable (determining that the penetration has reached equilibrium), and obtaining the test result. There are two main differences between the contact lens test and the soft package test: * is the sample clamping device is different, the sample shape and area difference is large; the second is the test environment is different, the standard film oxygen permeability test temperature It is 23 °C , and to test the contact lens, in order to simulate the actual use, choose a test temperature of 35 °C . Since the temperature change will significantly affect the results of the oxygen permeability test, the stability of the temperature during the test is very important, so the device has a certain temperature control function.

The oxygen permeability of the lens is an important indicator of the contact lens, and its level directly affects the comfort and even health of the wearer when wearing the lens. Based on the world-renowned barrier laboratory, Jinan Languang provides zui professional contact lens oxygen permeability testing instruments for the majority of contact lens manufacturers. It hopes to have extensive exchanges and cooperation with colleagues in the industry for the Chinese contact lens industry. The development of the development is a little bit weak.

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