The abbreviation NV-ADD on an eyeglass prescription stands for Near Vision Addition. This measurement provides the extra focusing power required for close-up tasks like reading or using a smartphone. It is necessary for people who need help seeing clearly at arm’s length or closer, a visual change that typically occurs as part of the natural aging process. Understanding this value helps demystify how a single pair of glasses can correct vision at multiple distances and restore comfortable near vision.
Defining the Near Vision Addition Power
The Near Vision Addition power, often labeled “ADD” on a prescription, is a specific amount of supplementary magnification for near tasks. This power is always a positive value, indicated with a plus sign, and is expressed in units called diopters (D). The measurement typically ranges between +0.75 D and +3.00 D, providing the necessary boost for reading at a comfortable distance.
This additional power is mathematically combined with the existing distance vision prescription to calculate the total power needed for the near-vision zone of the lens. For example, a distance prescription of -1.00 D and an ADD of +1.50 D results in a total reading power of +0.50 D. The ADD value is generally the same for both eyes, as the eye’s natural focusing ability diminishes equally. This fundamental number is used by lens manufacturers to create multifocal glasses.
Why Near Vision Addition Becomes Necessary
The physiological reason a person requires Near Vision Addition is presbyopia, an age-related condition. Presbyopia is the gradual loss of the eye’s ability to focus on close objects because the natural lens begins to harden and lose its elasticity over time.
The flexible lens is responsible for accommodation, where it changes shape to shift focus from far to near objects. As the lens stiffens, it cannot change its curvature sufficiently to focus light correctly onto the retina for close-up viewing. This condition commonly begins around age 40, and the required addition power gradually increases until the mid-60s. Symptoms include blurry near vision, eye strain, and the need to hold reading material farther away.
How Addition Power Shapes Different Lens Types
The NV-ADD measurement determines the required strength of the near-vision segment in multifocal lenses. Two primary lens designs utilize this addition power to restore clear near vision: bifocals and progressive addition lenses. Bifocal lenses feature two distinct zones of correction: the main upper portion for distance vision and a smaller, visible segment in the lower part for near vision. The ADD power is concentrated entirely within this distinct lower segment.
Progressive addition lenses (PALs) offer a more advanced solution by providing a seamless transition between distance, intermediate, and near vision without visible lines. In a progressive lens, the ADD power gradually increases as the eye moves down the lens, from the distance zone at the top, through the intermediate corridor, to the full near-vision power at the bottom. This continuous power change allows for clear vision at all distances, unlike bifocals which only offer two fixed focal points.
Adapting to Glasses with Near Vision Addition
Wearing glasses with Near Vision Addition, particularly progressive lenses, requires a period of adjustment as the brain learns to process the new visual information. The adjustment period typically ranges from a few days up to two weeks, though some people may take up to a month. Initial symptoms may include a feeling of “wobbliness,” slight peripheral distortion, or minor dizziness as the eyes and brain acclimate to the power gradient.
Successful adaptation requires learning new head and eye movement habits. To focus on near objects, wearers must look down through the lower portion of the lens. Instead of moving only the eyes from side to side, a person should turn their head toward the object of focus to look through the clearest part of the lens. Wearing the new glasses consistently, rather than switching back to old pairs, is the most effective way to shorten the adaptation time.