He gave the boy’s ear a painful tweak.

他用力拧一下那男孩的耳朵。

This causes it to polymerise and then change shape, which means the ophthalmologist can tweak the lens to alter its power.

这束光使人工晶体上的光敏物质，改变形状，这意味着眼科学家能够调节这些晶状体来改变它的功效。