An alternative to the Drop Ball Test for the measurement of ophthalmic glass fracture resistance.

The Drop Ball Test (DBT) has some distinct disadvantages both as a standard measurement for ophthalmic lens fracture resistance and as a research tool. The Static Test (ST) was devised to allow a load and enzrgy analysis of the DBT and enable more rapid and accurate testing of large ophthalmic lens samples. It was found that over 50% of the energy generated in the DBT is absorbed by the lens mount instead of the test lens. This means that the standard DBT height of 50 inches is more an indication of DBT components than lens fracture resistance. Static testing of non-tempered, heat tempered and chemically tempered lenses correlated well with former DBT studies. The ST, however, allowed lens fracture resistance to be represented in pounds-load, a value better understood practically and mathematically.