Soft Lenses

Soft Lenses are, as the name suggests, a soft plastic gel material called a hydrogel. They become soft due to the hydrophilic or "water-loving" property of the plastics used. The first materials were just 38% water content, but were still revolutionary in their day because they were much more comfortable than other lenses available at the time.

Oxygen is transported through the material in the water within the material.

As materials developed, more water was included in the lenses and at one stage 85% water content materials were being produced. However these were simply too fragile, so these higher water content lenses had to be made thicker in order to make them durable. This meant that the oxygen had further to travel and resulted in no extra benefit in terms of oxygen transmission. Also these high water content lenses were difficult to keep clean and so in time the industry settled upon 50-60% water content as being the optimum for the majority of uses. Some 38% lenses are still used, as are some 70% materials in special cases.

The 50-60% ceiling on water content effectively limited the maximum amount of oxygen that a soft lens could transmit. Soft lenses are very comfortable and so patients can be misled into thinking that their lenses were doing no harm, yet the cornea underneath the lens was being starved of oxygen. This has been the major problem with soft lens wear over the years, with practitioners constantly warning against overwear, and patients ignoring the warnings because of the intrinsic comfort of the lenses.

This led to the search for materials that could transmit the necessary levels of oxygen to sustain the cornea during the longer periods of wear that patients were demanding.