When the normal eye looks at a distance, without adjustment, the curvature of the crystal surface remains constant and the object is focused on the retina just enough to form a clear image. When looking close, the ciliary muscle contracts and the lens bulges forward through its inherent elasticity, allowing near objects to be focused on the retina for imaging. At the same time, eye assembly and pupil narrowing occur, ensuring the clarity of near vision. Therefore, through the regulation function of the eye, the eye can see far and near very clearly. As the eye ages, the lens gradually becomes solid and loses its original elasticity, so the regulating power gradually decreases. In addition, the strength of the ciliary muscle decreases, which is also a factor in reducing the power of accommodation. As a result of the weakening of the accommodation power, the clarity of the near object becomes less and less, and the near point gradually recedes. At the beginning, there is no inconvenience, but when the distance to the near point has exceeded the habitual distance for study or work, one will feel difficulty in seeing near, the nearness cannot last, stronger lighting is needed for reading, and even visual fatigue symptoms such as eye swelling and headache will appear. With the increase of age, around 40-45 years old, the power of adjustment gradually decreases, making it difficult to do near work. This physiological weakening of adjustment power due to age is called presbyopia, which is what we usually call presbyopia. Many people think that people with myopia will not spend their eyes, in fact, this statement is incorrect, in life we often see some myopic elderly people, when reading take off myopic glasses, and sometimes have to then move the book properly to the near or far, it is because they are nearsighted on the basis of the occurrence of different degrees of blurred eyes.