In multifocal lenses, what does the term 'addition' refer to?

In multifocal lenses, the term 'addition' specifically refers to the difference in power between the reading segment and the distance segment of the lens. This power change is necessary to allow the wearer to see clearly at different distances, primarily for near vision tasks. The addition is typically indicated in diopters and supplements the distance power to create an effective near vision power.

For example, if a patient has a distance prescription of +2.00D and the addition is +2.00D, the power for the reading portion of the lens would be +4.00D. Understanding this concept is crucial for optometric technicians, as it directly impacts how multifocal lenses are prescribed and fitted for patients, ensuring they can comfortably transition between viewing distances.

Other answer options do not accurately capture the meaning of 'addition' in this context. The total power of the lens, the distance between the lens surfaces, and weight distribution do not pertain to the specific adaptation of multifocal lenses to accommodate various visual tasks. Thus, recognizing the role of addition in facilitating proper vision correction is vital for effective lens fitting and patient care.