Oxygen transmissibility within the optic zone of soft toric lenses

Andrew Elder Smith and Tony Hough explain how new high-precision thickness measurement can help practitioners to better understand how oxygen delivery varies with power

Since the early 1980s there has been extensive discussion about how much oxygen gets through contact lenses to the cornea. With the introduction of silicone hydrogels this discussion has intensified, possibly due to increased funding from the major manufacturers to promote wider awareness of the clinical benefits of materials having enhanced permeability.1-4 Lens manufacturers quote oxygen transmissibility (Dk/t) values that appear to be more than adequate to meet the oxygen demand of the cornea in open eye conditions. However, the quoted values are universally based on the centre thickness of a -3.00D lens. One interesting and little-mentioned outcome of this is that the reference values published by manufacturers for the Dk/t of torics and spherical lenses are very similar as shown in Table 1.