What power is added to multifocal lenses to assist with presbyopia?

In the context of multifocal lenses designed to assist with presbyopia, the term "ADD" refers to the additional power that is incorporated into the lenses to help individuals see clearly at near distances. Presbyopia is a common age-related condition that affects the eye's ability to focus on close objects. As we age, the natural lens of the eye becomes less flexible, leading to difficulties when trying to focus on nearby tasks.

The "ADD" power is typically indicated in diopters and is added to the base lens prescription to create the appropriate strength in the lower segment of bifocals or trifocals. This additional power allows light to be focused correctly on the retina for closer viewing tasks, such as reading or sewing, providing a clear vision field at that distance.

For multifocal lenses, this capability is central to their design, as they cater to the varying visual needs at different distances. This is in contrast to "sphere," which refers to the spherical power for nearsightedness or farsightedness, "cylinder," which is used to correct astigmatism, and "focus," which is a more general term that does not specifically apply to the adjustment needed for presbyopia. Thus, the addition of the "ADD