User: How did humans cope with poor eyesight in the Middle Ages? Did all hunters and knights thus have 20/20 vision?
Assistant: The human eye evolved over many generations to enable excellent visual acuity in the range of wavelengths perceived as visible light.  However, less than a thousand years ago, minimal advancement had been made in the treatment of poor vision.  Although eyeglasses were invented in the 13th century, they were not widely available until the 17th century.  Furthermore, recommended treatments for poor vision during the Middle Ages were largely ineffective and even harmful, such as the application of blood or hot irons to the eye.  Thus many people with reduced visual acuity were unable to perform the activities of daily life and work, and often became destitute or dependent on charity.  The advent of eyeglasses in the 17th century greatly improved the ability of many people to perform useful work and be self-sufficient, although many types of vision impairment still require more advanced treatments.