In a prescription, a plus lens is primarily used for which condition?

A plus lens is primarily used to correct hyperopia, also known as farsightedness. In hyperopia, the light entering the eye is focused behind the retina, which can cause difficulty seeing nearby objects clearly. A plus lens helps to converge the light rays before they enter the eye, allowing them to focus correctly on the retina. This correction enhances the patient's ability to see objects up close.

While presbyopia may also be corrected using bifocal or multifocal lenses that include a plus lens for near vision, the primary condition specifically associated with the use of only a plus lens is hyperopia. Myopia, on the other hand, is typically corrected with minus lenses, which diverge the light rays to extend their focal point forward, directly onto the retina. Astigmatism is managed through cylindrical lenses, which adjust the light entering the eye differently along different axes. Thus, in the context of the question, the application of plus lenses is most directly associated with the treatment of hyperopia.