I know . And bifocals weren 't invented until the mid-1700s .
我知道,而且双焦镜片是在1700年中才发明出来的。
She had plastic bifocals hanging on a chain over her heavy chest .
她沉重的胸前面挂着一架塑料的双光眼镜。
Nowadays , this type of glasses is known as bifocals .
现如今,这种眼镜被称为双光眼镜。
Nowadays , these glasses are known as bifocals .
如今,这些眼镜被称作双光眼镜。
Once the trufocal lenses are adjusted , the entire field of vision is in focus , unlike bifocals and progressive lenses , which keep only a limited area in sharp focus .