Presbyopia is the gradual reduction in the amount that the eye can change its focus up close. The changes are the result of the continued growth of the biological lens inside the eye, and are a normal part of ageing. Presbyopia usually becomes noticeable between the ages of 40 and 50 as an inability to focus on near objects. People in this age group often find that they have to hold things further away to see them clearly. Presbyopia can be corrected by an optical prescription specifically designed for close work. This can be provided in many forms, including reading glasses, bifocals, trifocals and progressive lenses (multifocals).