- 1
Bifocals are glasses with two different strengths in one lens. The upper part is for seeing far away — a street, a board, a person across a room. The lower part is for seeing close — a book, a phone, a menu. You do not swap glasses. You look through the top or the bottom. Older people often need them when the eyes can no longer do both jobs with one pair. You can usually see a line across the glass where the two parts meet; some people dislike that line and choose a smoother lens instead. The word is almost always plural: we say a pair of bifocals, not a , unless we mean one lens. Ordinary, slightly clinical, not slang.
雙光眼鏡（上半看遠、下半看近；和漸進鏡片不同，中間通常有一條分界）
組成bi- means two; focal comes from focus, the point where light comes together. So the name is two focuses in one pair of glasses. John Isaac Hawkins coined bifocals in 1824; he also invented trifocals. Benjamin Franklin had the idea earlier, but he called them double spectacles.
原始詞典資料1 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
bifocalsnoun
- 1
Spectacles that have corrective lenses of two different powers; used by people who need both distance and reading glasses.
- He unfolded a pair of bifocals and thrust them as far up the bridge of his nose as possible.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。