The oxygen transmission performance of contact lenses would directly influence feelings and experiences of consumers, and, correspondingly, the sales volume of contact lenses would be affected. The test for oxygen permeation performance of contact lens has become a main concern of the manufacturers.

1. Title
Oxygen Transmission Performance Testing for Contact Lenses
Abstract The oxygen transmission performance of contact lenses would directly influence feelings and experiences of
consumers, and, correspondingly, the sales volume of contact lenses would be affected. The test for oxygen
permeation performance of contact lens has become a main concern of the manufacturers.
Keywords contact lenses, oxygen transmission, oxygen transmission rate, OTR, equal pressure method film/package
oxygen permeability tester
Body It’s well-known that the oxygen transmission performance of contact lenses would directly influence the
feelings and experiences of the consumers, and the sales volume would be affected correspondingly.
Therefore, the test for oxygen permeation performance of contact lens has become a main concern of the
manufacturers. Hereafter, Labthink Instruments Co., Ltd. will make a brief introduction to oxygen
transmission performance testing of contact lenses, based on OX2/231 equal pressure method film/package
oxygen permeability tester.
Owing to the importance of oxygen transmission performance of contact lenses, ISO, International Standard
Organization, has formulated two relevant testing standards as follows: ISO 9913-1, Optics and optical
instruments—Contact lenses—Part 1: Determination of oxygen permeability and transmissibility with the
FATT method; and ISO 9913-2, Optics and optical instruments—Contact lenses—Part 2: Determination of
oxygen permeability and transmissibility by the coulometric method. The testing principle and instrument of
ISO 9913-2 are similar to those of coulometric method applied in oxygen transmission rate tests for flexible
packaging materials. The testing principle is as shown in Fig. 1.
Testing principle is explained hereafter: place the sample to be tested into the testing chamber, and the
chamber would be separated into two sections: upper chamber and lower chamber. Then, testing gas with a
certain oxygen concentration is purged into the upper chamber. Carrier gas flow, that is, nitrogen gas flow,
purges into the coulometric sensor through the lower chamber. Though the pressures of the upper chamber
and the lower chamber are the same, the pressures of oxygen differ in them. Thus, oxygen would, with the
help of concentration difference, permeate through the sample and into the carrier gas side. Then, oxygen
would be taken to the coulometric sensor. The sensor would precisely measure the oxygen quantity in the
carrier gas flow (that is, nitrogen gas flow), and calculate the oxygen transmission rate (OTR).
It can be concluded, from the above-mentioned principle, that oxygen transmission performance tests for
contact lenses and flexible packaging materials have the following steps in common: first, system zero is

2. achieved by purging. Second, oxygen gas flow is purged into the upper chamber. Third, the sensor output is
stable (to determine whether transmission equilibrium has been realized). Fourth, testing results can be
obtained.
Before testing, instruments should be calibrated with reference films, so as to confirm the correction factors.
Those factors would be used in formal tests. It’s stated clearly in ISO 9913-2 that the sample for calibration
is SRM 1470, which coincides with the reference film stipulated in ASTM D 3985, a standard for film
testing.
However, there are differences in the tests for contact lenses and flexible packaging materials. First, the
clamping structures are different. The shapes and sizes of the sample are quite different. Second, testing
environments are different. The standard temperature for film oxygen transmission testing is 23℃, and that
for contact lens is 35℃, so as to imitate actual temperature in usage. Meanwhile, temperature change would
influence the oxygen transmission testing results remarkably, and the stability of testing temperature has
become very important.
Labthink, based on her professional oxygen transmission rate tester for flexible packaging materials,
TOY-C2 equal pressure Film/Package Oxygen Permeability Tester, has specially designed and manufactured
the clamping accessories and temperature control device for oxygen transmission tests of contact lenses. The
special shape of the sample and the special need for testing temperature have been meet, so that the testing
demands for oxygen transmission performance of contact lens can be fully satisfied.
Besides oxygen transmission performance testing, other indexes has to be monitored, so as to confirm actual
usage and the working life of the contact lenses. For more information, please visit www.labthink.cn/en.
Labthink Instruments Co., Ltd. Labthink Instruments Co., Ltd. would like to have more communications
and co-operations with the industry.
Contact Yarina Gao
Marketing Department
Email: trade5@labthink.cn
Tel: 86-531-85062108
Labthink Instruments Co., Ltd
www.labthink.cn/en