Bifocals Lenses yog cov tsom iav tsom iav uas muaj ob qhov chaw kho thiab feem ntau yog siv rau kev kho presbyopia. Qhov chaw uas bifocals kho qhov pom kev deb yog hu ua thaj chaw pom kev deb, thiab thaj chaw uas kho qhov ze ntawm qhov pom kev yog hu ua ze thaj chaw pom kev thiab thaj chaw nyeem ntawv. Feem ntau, thaj chaw deb yog qhov loj dua, yog li nws tseem hu ua lub ntsiab daim, thiab thaj chaw ze yog me dua, hu ua sub slice.