The very most accurate biological watch in the human body, is the state of presbyopia, that occurs around the age of 45 (40-50). The lens of the eye is no longer as elastic as it was in young age, and loses the ability to focus on near objects.
A +lens is needed, most often reading glasses to prescription or ready-to-wear reading glasses. From this day on, the person is doomed to wear a pair of reading glasses to be able to read anything that is small and positioned close to the person,
– a condition that only gets worse the older one gets and the dimmer the light is.