Presbyopia is an aging eye. All parts of our body may lose their function with aging. The representative aging diseases in the field of ophthalmology are cataract and macular degeneration. Presbyopia is also a natural aging phenomenon that people has difficulty in focusing on near subject. There is a structure called lens in our eye and the function of lens is a refraction of lignt. Lens helps us focusing an object that we want to see with changing its thickness. When we try to focus on near subjects, ciliary muscle contracts to release the lens zonule and the lens becomes thicker. When we try to see far subjects, ciliary muscle relaxes and lens becomes thinner. These changes of lens thickness occurs very fast in young people, but with aging, the speed of changing the thickness of lens becomes slow. Finally, aged people can't change the lens thickness and can't focus on near subject without the help of near glasses and so on. In this case, we call it presbyopia.