Ophthalmic glass

Claim 1

A LITHIA-FREE OPHTHALMIC GLASS WHICH COMPRISES 33% TO 55% SIO2, 1% TO 7% B2O3, 2% TO 15% ZRO2, 5% TO 15% OF AN ALKALI METAL OXIDE SELECTED FROM THE GROUP CONSISTING OF NA20 AND MIXTURES OF NA2O AND K2O, AND AT LEAST TWO BIVALENT METAL OXIDES IN THE INDICATED PROPORTIONS SELECTED FROM THE GROUP CONSISTING OF UP TO 28% BAO, UP TO 15% PHO, 3% TO 15% CAO, 3% TO 15% ZNO, 3% TO 15% SRO, 3% TO 15% CDO, AND 3% TO 30% OF A MIXTURE OF A PLURALITY OF CAO, ZNO, SRO, AND CDO, THE MAXIUM PROPORTION OF ANY SUCH OXIDE IN SAID MIXTURE BEING 15%, THE SELECTED BIVALENT METAL OXIDES INCLUDING AN OXIDE SELECTED FROM THE GROUP CONSISTING OF CAO, ZNO, SRO, CDO, AND A MIXTURE OF A PLURALITY OF SUCH FOUR OXIDES IN THE ABOVE-INDICATED PROPORTION, THE TOTAL PERCENTAGE OF THE BIVALENT METAL OXIDES BEING BETWEEN 15% AND 50%, THE SOFTENING POINT BEING BELOW 750*C., THE REFRACTIVE INDEX (ND) BEING BETWEEN 1.57 AND 1.70, AND THE THERMAL EXPANSION COEFFICIENT BEING BETWEEN 70X10**-7 AND 97X10**-7 CM. PER CM. PER *C BETWEEN 0* AND 300*C.