Presbyopia is a condition in which the lens loses its flexibility, making it difficult to focus on close objects. Usually in their early 40s, people begin to experience blurred vision at near points, such as when reading or working at the computer. They may even develop headaches or eyestrain, or begin to feel fatigued. Presbyopia happens to everyone at some point in their life, even if they never had a vision problem before.

Presbyopia is caused by an age-related process, rather than the way light is refracted, or bent, by the eye. These age-related changes occur within the proteins in the lens, making the lens harder and less elastic with the years. Similar changes also take place in the muscle fibers surrounding the lens.

Glasses with bifocal lenses are the most common correction for presbyopia. At the John-Kenyon American Eye Institute, presbyopia can be treated with a procedure called PRELEXSM.