Considerations

Rigid Lens Materials

Gas permeable lenses have been available for over thirty years. What was an exciting innovation in materials from the perspex lens that transmitted no oxygen, gradually became an obsession in chasing oxygen permeability to the dizzy heights that it has now achieved. What many ECPs have forgotten is that PMMA lenses, despite their lack of permeability, worked to a great extent.

Oxygen was and is now, delivered to the cornea via the tear pump mechanism. So do we really need materials with ≥ 100Dk? In some cases the answer is yes. In a soft lens where the cornea is entirely covered and therefore has a negligible tear exchange, we need to maintain approximately 35Dk to the cornea in daily wear. In some rigid designs such as the semi-scleral, this is also the case, as well as for the increasing demand for intra-limbal large diameter designs. However, a 60Dk material should be more than suitable for a standard diameter lens with good movement. This is particularly true if the lens is wettable and stable.

The higher Dk materials are ideal for the high-demand cornea, larger lens designs and higher prescriptions, but for most regular fits the 60Dk Optimum Comfort material should be the material of choice. Optimum Classic has a lower Dk, but the advantage of offering a higher refractive index, which will result in a thinner lens. Optimum Extra is recommended for larger lens designs and semi-sclerals, and Optimum Extreme when additional oxygen is required for overnight wear, as in ortho-k.

Soft Lenses

The traditional soft lens materials are increasingly being replaced by silicone hydrogels. This trend will continue as materials and availability improve, and most new fits will probably be best served with a silicone hydrogel material. In some markets, where costs or durability may be of concern, the traditional hydrogels may persist, but in the long term silicone hydrogel should be the material of choice for both new and existing patients coming through the practice for re-fitting.