Presbyopia is the common name, but the medical term is “presbyopia”. 1. An important reason why a normal person is able to see objects clearly in the distance or near is because of the “adjustment” of the eye itself. The result of the regulation is that regardless of the object’s distance, it can be just focused on the fundus of the eye, forming a clear image, just like a foolproof camera can always take a clear picture of distant and near objects. When the human body is seeing things, this “adjustment” effect is always going on, and is continuous (a bit like the characteristics of the continuous function of mathematics), but you do not easily notice. For young people who can drive a car, let’s use an analogy, just like when driving an automatic car, when you step on the gas pedal, the gears are also changing in sync with the change in speed to match the two. For healthy young people, this “adjustment” function is not a problem, so see far and near will not have problems. 2, presbyopia, is the above adjustment problems. The performance in can not freely look far and look at the near, especially look at the near, because, look at the near need to have a higher adjustment, but, they can not meet this “higher” need, equivalent to the car transmission failure, have to use external forces – presbyopic glasses. 3, the usual presbyopic glasses is with two pairs of, one pair to see far, one pair to see near with, the so-called see far means walking with, see near is reading newspapers, writing, etc. with. This is equivalent to a car without a gearbox, artificially set two fixed speed. 4, in reality, most people usually have two pairs of presbyopic glasses, so can you have three or more pairs? In theory, there is nothing wrong with it, let’s say, the general household kitchen utensils, two kitchen knives are enough, one cut meat, another cut vegetables, but, if equipped with a fruit knife or butter knife, is it possible? Of course you can, but it is too much trouble, neither commonly used, and there is no place to put. By the same token, an elderly person, go out with five pairs of glasses, how troublesome it is.