A single vision lens and a distance lens are often confused. These terms describe two distinct concepts in optics: one refers to the physical design of the lens, and the other to the functional requirement of the wearer. Understanding this distinction is necessary to select the correct corrective eyewear and accurately interpret an eye prescription.
What Defines a Single Vision Lens
A single vision lens contains only one uniform optical power across its entire surface. This means the lens has a consistent focal length, making it capable of correcting vision for only one specific viewing distance. This lens design is the most common and simplest type prescribed by eye care professionals.
This uniformity contrasts directly with multifocal lenses, such as bifocals or progressives, which incorporate multiple distinct powers in different zones. The single vision design corrects specific refractive errors, including myopia (nearsightedness), hyperopia (farsightedness), or astigmatism.
Understanding the Three Zones of Vision Correction
Vision correction requirements are categorized into three primary functional zones, based on the distance of the object being viewed from the eye. These zones describe the actual focus requirement, not the type of lens used to meet it.
Distance Vision
The Distance Vision zone is for objects far away, typically considered anything beyond arm’s length, and is the focus area used for activities like driving or watching television.
Intermediate Vision
The Intermediate Vision zone addresses objects at arm’s length, which is crucial for tasks like working on a desktop computer, viewing a car’s dashboard, or looking at items on a grocery shelf. This mid-range focus is a significant demand in modern life.
Near Vision
The Near Vision zone is for objects held close to the eye, generally within 12 to 16 inches, which includes reading a book, using a smartphone, or performing intricate close-up work.
The need for correction in these zones is determined by the natural mechanics of the eye and any existing refractive errors. When an eye exam determines a prescription, the power required for each functional zone is measured separately. This functional requirement dictates where the focus point of the correction needs to be.
Why Single Vision is Not Always Distance Vision
The core distinction is that “single vision” is a lens design type, while “distance vision” is a functional requirement. A single vision lens delivers one power, which can be prescribed to correct any of the three functional zones.
For example, a person with myopia (nearsightedness) who needs correction for driving will receive a single vision lens ground to correct their Distance Vision.
However, a person with presbyopia, an age-related condition that impairs near focus, might receive a single vision lens ground specifically for their Near Vision requirement. These are commonly known as reading glasses and contain a uniform power meant only for close-up tasks.
Similarly, a dedicated pair of computer glasses can be made with a single vision lens ground to correct only the Intermediate Vision zone. While a distance lens is almost always a single vision lens, the reverse is not true; a single vision lens may also be a near or intermediate lens.