A contact lens, or simply contact, is a thin lens placed directly on the surface of the eye. Contact lenses are considered medical devices and can be worn to correct vision, or for cosmetic or therapeutic reasons.

Contact lenses can be classified into three types by their materials, soft lenses, rigid lenses and hybrid type lenses which consist of a rigid center and a soft “skirt”. Classified by their functions, contact lenses can be classified into corrective contact lenses, cosmetic contact lenses, therapeutic scleral lenses and therapeutic soft lenses.

Normally our eyes need breathe and the oxygen is mainly from the air. If the oxygen permeability of the contact lens is insufficient, the corneas may be deficient in oxygen. As a result, the eyes may feel uncomfortable and even worse, eye disease may be caused for long term use of such contact lenses. Therefore, the oxygen permeability shall be the most important factor that we should consider when selecting contact lenses. For the manufacturers of contact lenses, they should monitor the quality of their products by testing the oxygen transmission rate.

This article provides a test method of oxygen permeability of contact lens for your reference. The test specimen we used are rigid contact lenses provided by one manufacturer. The testing instrument we used is Labthink’s OX2/231 Oxygen Transmission Rate Tester.

Figure 1. Contact Lenses with Different Colors

Figure 2. OX2/231 Oxygen Transmission Rate Tester

In the tests, the pre-conditioned specimen is mounted between the upper and lower chambers at ambient atmospheric pressure. One chamber contains oxygen and the other chamber is slowly purged by a stream of nitrogen. Due to the concentration difference between the two chambers, oxygen molecules permeate through the specimen into the nitrogen side and are taken to the coulometric sensor where proportional electrical signals are generated. The oxygen transmission rate is then obtained by analyzing and calculating the signals. For package samples, high purity nitrogen flows inside the package, and oxygen flows outside.

The tests shall be performed according to the following procedures.

(1)   Take the contact lens out of the physiological saline. Place the contact lens on the surface of lower test chamber. Make sure the contact lens is free of creases or folds. Then close the upper test chamber and make the O-ring with vacuum grease contact the surface of the contact lens so that the contact lens is sealed between the upper and lower test chamber.

(2)   Set test temperature 35℃ and test humidity 95%RH. Set test mode and other test parameters. Then click Start Test to start the tests.

(3)   The tests will be automatically completed. The test results will be calculated and displayed automatically after the tests.

With the test results, the manufacturer can adjust the manufacturing technique to improve the oxygen permeability of their contact lenses by changing the material, thickness or water content.

For more details about OX2/231 Oxygen Transmission Rate Tester, please visit www.labthink.com

About Labthink Instruments Co., Ltd:

Labthink Instruments Co., Ltd is one leading supplier of packaging testing instruments, which is headquartered in Jinan, China and operated in Boston, U.S.A.