How long should I change my prescription?

[rimless eyeglasses]

I have bought my prescription glasses for two years. And it still can work. But my wife told me that I should change a new one. She said prescription eyeglasses can not wear for a long time. Why? I think I could see clear by my prescription glasses. Why should I change? And how long should I change my prescription? If I still wear my old prescription. Can it hurt myself???