| Abstract: oxygen permeability, OTR of contact lens, | | | | ISO 9913-2 is suitable for rigid and non-hydrogel |
| which has a direct influence on wearer amenity, is an | | | | flexible contact lens materials. The testing indexes are |
| important index of contact lens. This article deals with | | | | oxygen flux-j, oxygen permeability -Dk, oxygen |
| the importance, influencing factors and testing method | | | | transmissibility-Dk/t and specimen thickness-t. Generally, |
| of oxygen permeability of contact lens | | | | Dk is used to evaluate the permeability index of |
| Keywords: contact lens, oxygen permeability, | | | | contact lenses. Testing principle is illustrated as fig. 1: put |
| moisture content and oxygen permeability testing | | | | specimen into testing chamber to divide the chamber |
| | | | | into upper and lower parts. Fill testing gas into upper |
| Speaking of contact lenses, the most common thing | | | | chamber with the oxygen content at a fixed rate. |
| we thought of is their 'contact' effect. Contact lenses | | | | Carrier gas flows into coulometric sensor from lower |
| correct vision by directly adhering to the surface of | | | | chamber, by which an equal pressure between two |
| eye cornea to change diopter. Therefore, they | | | | sides of the specimen is maintained. However, oxygen |
| possess a lot of unique merits comparing with frame | | | | partial pressure is different. Under the function of partial |
| glasses. For example, it applies no compression to | | | | pressure, oxygen will transmits into carrier gas through |
| nose bridge and ears, and is especially applicable to | | | | film and will be carried into coulometric sensor, where |
| some special professions such as actor and athlete. | | | | oxygen quantity in nitrogen gas can be calculated |
| Actually, the functions of contact lenses are not limit to | | | | accurately and then oxygen transmissibility of the |
| the correction of shortsightedness, farsightedness and | | | | material can be calculated. Oxygen permeability |
| astigmatism. They have other functions such as | | | | instrument should be calibrated with reference film |
| treating color blindness and some ophthalmocace by | | | | before testing to determine the calibration factor, which |
| medication absorption. | | | | will be used in calibration. It is regulated in standard ISO |
| | | | | 9913 that calibration specimen SRM 1470 is the same |
| 1. Material Requirements of Contact Lens | | | | as that used in standard ASTM D 3985 for film testing. |
| Wearers attach particular importance to the | | | | Testing process includes the following steps: purge |
| selection of lens material because it adheres directly to | | | | system, diverge oxygen gas into upper chamber, |
| eye cornea. With the influence of advertisement, many | | | | sensor output becomes stable (judging whether |
| wearers go in for lenses of high moisture content in | | | | transmitting achieves equilibrium), and obtain testing |
| selecting contact lenses. In their eyes, the higher the | | | | result. There are mainly two differences between |
| moisture content, the better the lens quality. In fact, the | | | | testing of contact lenses and flexible package testing: |
| pursuit of higher moisture content is very wrong in | | | | one is the specimen fixture, specimen shape and area; |
| contact lens selection. Wearers should also take | | | | the second difference is testing environment. Testing |
| secretory volume of tears, working and living | | | | temperature of film oxygen permeability is 23?. To |
| environment into account. Actually, oxygen permeability | | | | simulate practical service condition, testing temperature |
| of lenses is the most important index. The discomforts | | | | of contact lenses is 35?. Since temperature fluctuation |
| and wearing time mainly depends on lens oxygen | | | | has an obvious influence on testing results of oxygen |
| permeability. Moreover, higher moisture content and | | | | permeability, the stability of testing temperature is of |
| ultra thin that are advertised now are to improve lens | | | | great significance. Therefore, it is better that the |
| oxygen permeability. | | | | instruments possess function of temperature |
| Oxygen deficit, which is caused by inability of eye | | | | controlling, just as Labthink TOY-C2 Oxygen |
| cornea to obtain oxygen, is the most common trouble | | | | Permeability Tester. |
| of wearing contact lenses. Originally, cornea breathes | | | | |
| by obtaining oxygen from air directly. When contact | | | | 3. Influence of Lenses Suitability on Oxygen |
| lens adheres to eyeball surface, oxygen can still | | | | Permeability |
| transmits through lenses, but the transmitting rate | | | | Whether contact lenses are suitable mainly depends |
| reduces obviously. Newly increased vessel caused by | | | | on the perfection of suitability. A pair of good contact |
| cornea oxygen deficit will appear as red heron and will | | | | lenses should match with eye cornea perfectly. There |
| increase the opportunity of infection of eyes. For that | | | | is a layer of tear existing between contact lens and |
| reason, contact lenses of higher oxygen permeability | | | | eye cornea, and is constantly flowing. The tears bring |
| should be selected. Oxygen permeability of lenses is | | | | oxygen to cornea and take off waste substance. In |
| related with lens moisture content and lens thickness | | | | this way, contact lenses will not change the normal |
| because oxygen is transmitted by water. However, | | | | physiological condition of eyes and will not impair eye |
| the crucial factor that influences wearing effect is | | | | cornea. If the contact lens doesn't match well with eye |
| whether contact lenses match eye cornea. | | | | cornea, even ultra thin lenses of high moisture content |
| | | | | will adhere closely to the cornea with the result that |
| 2. Oxygen Permeability Testing | | | | the flowing of oxygen can only rely on moisture |
| As mentioned above, oxygen permeability of | | | | content and thickness of the lens. Of course, high |
| contact lenses has a direct influence on wearer | | | | oxygen permeability is always favorable, no matter |
| comforts and will in turn affect the sales. That is why | | | | what the kind of suitability is. |
| oxygen permeability testing attracts particular attention | | | | |
| of lens manufacturers. | | | | 4. Conclusion |
| ISO issued special testing standards for the oxygen | | | | Oxygen permeability of contact lens, which has a |
| permeability testing of contact lenses: ISO 9913-1 | | | | direct influence on wearing comforts, is an important |
| Optics and Optical Instruments-Contact Lenses-Part 1: | | | | index. That is why manufacturers of various contact |
| Determination of Oxygen Permeability and | | | | lenses are trying their best to improve oxygen |
| Transmissibility with the FATT Method and ISO 9913-2 | | | | permeability of contact lenses. At present, the |
| Optics and Optical Instruments -Contact Lenses-Part2: | | | | marketing of PGP has obviously influenced market |
| Determination of Oxygen Permeability and | | | | share of traditional flexible contact lenses. The |
| Transmissibility by the Coulometric Method. Testing | | | | outstanding merit of RGP is high oxygen permeability, |
| principal and testing instruments in ISO 9913-2 is very | | | | which makes no oxygen deficit of eye cornea. With |
| similar to that used in coulometric method in oxygen | | | | RGP, many complications caused by flexible contact |
| permeability testing of flexible material. Many | | | | lenses can be avoided. Therefore, RGP has become |
| manufacturers of contact lens have been authorizing | | | | known and encouraged by most experts. |
| Labthink to test the oxygen permeability of lens | | | | Further information please feel free to contact |
| materials and have got ideal testing results. | | | | Shirley Wu via trade2@labthink. |