The terms “single vision” and “distance” are often confused when people review their eyeglass prescriptions. They are not interchangeable, but they are closely related in optics. Single vision describes the physical design of the lens, meaning it holds only one optical power across its entire surface. Distance, conversely, refers to the specific focal area the lens is designed to correct. While single vision lenses are most commonly prescribed for distance correction, they are distinct concepts.
Defining Single Vision Lenses
A single vision lens is characterized by having a uniform power from edge to edge. This means the lens provides the exact same degree of refractive correction regardless of where the wearer looks through it. This design contrasts with multifocal lenses, such as bifocals or progressives, which contain multiple prescriptions. The lens addresses a single refractive error, such as myopia (nearsightedness), hyperopia (farsightedness), or astigmatism. This lens type is the most widely prescribed due to its simplicity and suitability for correcting a singular vision issue.
Understanding Focal Areas
Vision correction is categorized into three primary viewing zones, defined by the object’s distance from the eye. These zones determine the required power of any lens. The first zone is distance vision, which covers anything beyond 20 feet, such as driving or viewing scenery. The next zone is intermediate vision, covering objects at arm’s length, typically between 20 inches and 5 feet, essential for computer work. Finally, near vision is the closest zone, necessary for reading or viewing a smartphone, usually requiring focus at 12 to 16 inches.
Single Vision: A Lens Applied to Any Focal Area
The confusion exists because a single vision lens can be manufactured to correct vision for any of the three focal areas. Single vision describes the how—one power throughout the lens—while distance, intermediate, or near describes the what—the specific prescription power needed for that range. A nearsighted person typically uses a single vision lens to correct their primary need, which is distance vision. However, single vision lenses can also be made specifically for reading (“readers”), applying a uniform plus power to correct only near vision. They can also be optimized for the intermediate range, such as for computer use. Distance is simply one of the three potential uses for a single vision lens, not a synonym for the lens type itself.