Oxygen-transmissibility considerations for a hard-soft contact-lens combination.

A combination formed by covering a soft contact lens on the cornea with either an oxygen-permeable or an impermeable hard lens offers some advantages over a soft lens or a hard lens alone. Several procedures can be used to fit such combinations to the eye. The amount of oxygen that is delivered to the cornea will depend strongly on the fit on the soft lens to the cornea and the fit of the hard lens to the soft lens; the amount of oxygen delivered by 4 different combinations is described here. The results show that the proper choice of lenses and fit will permit an adequate supply of oxygen to reach the cornea in daily wear.