As I know that it is not bad for the eyes if you wear OTC reading glasses properly. They can be understand as already made reading glasses. Although you are not require offer prescription, you shall know your power of your eyes so as to choose properly OTC reading glasses for vision aids. And they are the same as prescription to some extent. If you choose properly OTC reading glasses, they won't cause many damages about your eyes.
Ready-made reading glasses are one-size-fits-all. They have the same power in each eye. Most commonly, we do not have the same prescription in both eyes for best clarity.However,they are great for a back up when travelling, or kept in the glove box of the car. They are great in the garage or hobby workshop where a good pair may get ruined by grease and dirt. They are better economically if you lose your glasses every second week!They are cheap and cheerful for what they can do. But they are best used only for very short periods to avoid eyestrain and headaches.