a biconcave lens的用法和样例：
- a biconcave lens.
- Red blood cell with a biconcave disc shape is to provide a large surface area to volume ratio to facilitate the diffusion of gases. (NOT to carry more oxygen.
- A close- up lens is ideal for taking close- up picture.
- In this operation the surgeons implant a new lens (in the eye).
- There is a vein of melancholy in his character.