A contact lens design using a particular material will require the measurement of Oxygen Permeation. Materials with higher permeation rates together with thinner lenses will perform better, providing greater comfort during use. However, simply choosing the material with the highest permeation rate and making the lens thin is not an easy option. The lens shape and thickness varies with the prescription. A focal length of -3.00 Dioptres has been chosen as the standard for Oxygen Permeation measurement. The thickness in the central region of the lens is used because this covers the most critical area of the cornea.
The highest permeability materials are difficult to manufacture into thin lenses, resulting in a range of designs. The aim is to provide the highest Oxygen permeation rate to maximise corneal oxygenation which directly corresponds to comfort and visual performance. The latest silicone Hydrogels do not have their oxygen permeability governed by water content alone, but also by their constituent siloxane groups. Contact lenses containing these products are some of the highest performing currently available, with very high oxygen transmission rates and the highest levels of comfort.
The international standard, ISO 18369-4:2006 describes the measurement of permeability transmission for finished lenses rather than a material sample. This oxygen transmission value is subsequently converted into the permeability value by measuring the lens thickness.
The Systech Illinois 8001 Permeation Analyser can be utilised for both the development of new contact lens material and also for certifying the finished products to the ISO standard.