Shows Otr
The oxygen permeability, OTR Contact Lens Materials
Abstract: oxygen permeability, OTR contact lens, which has a direct influence on the leisure user, is an important index of contact lenses. This article discusses the importance, influence factors and test method of oxygen permeability contact lenses
Keywords: contact lenses, oxygen permeability, moisture content and oxygen permeability tests
Speaking of lenses, the most common is the idea of 'contact' effect. Contact lenses correct vision directly attached to the surface of the cornea of the eye to change diopters. So have a lot of unique advantages in comparison with glasses frame. For example, applying any compression bridge of the nose and ears, and is especially applicable to some special professions, such as actor and athlete. In reality, the role of contact lenses are not limited to the the correction of nearsightedness, farsightedness and astigmatism. They have other functions as the treatment of color blindness and some absorption by ophthalmocace medicine.
1. Material Requirements Contact Lens
Carriers of particular importance to the selection of the lens material, because it adheres directly to the cornea of the eye. With the influence of advertisers, users of many lenses to go high moisture content in the selection of lenses contact. In their eyes, the higher the moisture content, the higher the quality of the lens. In fact, finding a higher moisture content is very wrong in the selection of lenses contact. Users also must have the volume of tear secretion, working and living in mind. In fact, the oxygen permeability of lenses is the index more important. The inconvenience and time of use depends primarily on the permeability of the lens of oxygen. Moreover, higher moisture content and fine that advertise now are to improve the oxygen permeability of the lens.
The oxygen deficit, which is caused by the inability of the cornea of the eye to get oxygen, is the most common problem of contact lens use. Originally, it breathes the cornea by obtaining oxygen directly from air. When adhering to the lens surface of the eyeball, can still transmit oxygen through lenses, but the rate of transmission is reduced obviously. New vessels caused by the cornea, oxygen deficit appear as red herons and increase the chance of eye infection. For this reason, contact lenses oxygen permeability higher should be selected. Oxygen permeability of lenses is related to the moisture content of the lens and lens thickness since oxygen is passed by water. However, the key factor influencing whether the effect is use contact lenses match the cornea of the eye.
2. Permeability test oxygen
As mentioned above, the oxygen permeability of contact lenses has a direct influence on user comfort and will an effect on sales. For this reason, the oxygen permeability test draws particular attention to lens manufacturers.
ISO issued special rules test to test oxygen permeability of contact lenses: ISO 9913-1 Optics and optical instruments, contact lenses-Part 1: Determination of oxygen The permeability and transmissibility with the method of fats and ISO 9913-2 Optics and optical instruments, contact lenses-Part 2: Determination of permeability oxygen transmissibility of the coulometric method. Home testing and test instruments in ISO 9913-2 is similar to that used in the method of coulometric test oxygen permeability of a flexible material. Many manufacturers of contact lenses have been authorizing Labthink to test the oxygen permeability of materials lenses and are ideal test results.
ISO 9913-2 is not suitable for rigid and hydrogel contact lens materials flexible. The indices of the tests are the flow of oxygen-j,-DK oxygen permeability, oxygen transmissibility Dk / t and the sample thick-T. In general, DK is used to evaluate the permeability index contact lenses. Test principle is illustrated in Fig. 1: sheet placed in the test chamber for dividing the chamber at the top and bottom. The landfill gas testing in the upper chamber with the oxygen content at a fixed rate. The carrier gas flows into the sensor coulometric of the House, by maintaining an equal pressure between the two sides of the sample. However, the partial pressure of oxygen is different. Under the function of the partial pressure of oxygen in the carrier gas passes through the film and will be in the coulometric sensor where the amount of oxygen in the nitrogen gas can be calculated accurately oxygen transmissibility and then the material can be calculated. Instrument oxygen permeability should be calibrated with a reference film before the test to determine the factor calibration to be used in the calibration. It is regulated by ISO 9913 that calibration sample SRM 1470 is the same as that used in standard ASTM D 3985 for testing film.
Testing process includes the following steps: purge system, oxygen gas diverge in the upper house, the sensor output becomes stable (judging whether the transmission reaches equilibrium), and obtain the test result. There are two main differences between evidence of contact lenses and flexible package testing: one is the model lamp, an exemplary and area, but the second difference is the test environment. The test temperature of film permeability oxygen is 23?. To simulate practical service condition, temperature of the contact lens fitting is 35?. As the temperature fluctuation is an obvious influence on the results of oxygen permeability tests, the stability of the test temperature is of great importance. Therefore, it is better than the instruments have the temperature control function and Labthink TOY-C2 oxygen permeability Tester.
3. Influence of lens competence in the oxygen permeability
If contact lenses are suitable mainly depends on the perfection of suitability. A pair of contact lenses must coincide with good cornea of the eye perfectly. There is a tear layer between lens and cornea of the eye, and is in constant flux. Tears to carry oxygen to off the cornea and waste substances. Thus, the lenses will not change the normal physiological condition, eyes and not damage the cornea of eye. If the lens does not adapt well to the cornea of the eye, including ultra-thin lenses of high moisture content adheres closely to the cornea with the result that oxygen flow can only rely on the moisture content and thickness of the lens. Of course, the high oxygen permeability is always positive, no matter what the type of ability is.
4. Conclusion
Oxygen permeability of contact lenses, which has a direct influence on the use amenities is an important index. For this reason, manufacturers of contact lenses are different doing their best to improve the oxygen permeability of contact lenses. Currently, marketing of PGP has obviously influenced the market share of traditional flexible contact lenses. The exceptional merit is highly permeable RGP oxygen, which makes no oxygen deficiency in the cornea of the eye. With RGP, complications caused by flexible contact lenses can be avoided. Hence, RGP has known and encouraged by most experts.
For more information please contact Shirley via trade2@labthink.cn Wu, skype: Shirley labthink, MSN: shirleywu_labthink@hotmail.com.
About the Author
The Twifties Show – OTR – On the Road to Mt. Hood, Oregon