I want to know the answer to the following question:
What property of thorium oxide has caused it to no longer be used in eyeglasses?
All the background I'm provided with is that "Thorium oxide gives glass a high refractive index and low dispersion and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eyeglasses.[citation needed]". Is that enough to answer the question?