Varifocal glasses, also known as progressive lenses, are a solution for presbyopia, an age-related condition that makes focusing on close objects difficult. These lenses consolidate multiple vision corrections into a single lens. They provide clear vision for all distances—far, intermediate, and near—by utilizing a gradient of lens power, eliminating the need to constantly switch eyewear for different tasks.
The Progressive Design of Varifocal Lenses
Varifocal lenses rely on a graduated surface that alters the optical power across the lens, mimicking the natural way the eye focuses. The lens surface is divided into three primary viewing zones to accommodate different activities.
The top portion of the lens is dedicated to distance viewing, used for activities like driving. As the gaze moves downward, the lens power gradually changes through the intermediate zone. This middle section is calibrated for tasks within arm’s length, such as working on a computer or viewing a car’s dashboard.
The prescription continues to increase in power into the bottom portion of the lens, which is the near viewing or reading zone. This area contains the full power needed for close-up tasks like reading. The transition between these zones occurs along the progressive corridor, where the lens power smoothly increases without any visible lines on the lens surface.
This smooth, continuous change in power contrasts with the abrupt change of a step. However, compressing multiple prescriptions onto a single curved surface necessitates a trade-off. This design results in areas of peripheral distortion, sometimes described as the “swim effect,” on the outer edges of the lens.
Looking through these distorted side areas can cause objects to appear warped or blurry. Higher-quality varifocals are designed to minimize this distortion, pushing the blurry zones further toward the edges and widening the central corridor of clear vision. Users must learn to utilize the central corridor for clear vision and avoid looking through the periphery by turning the head instead of just the eyes.
Varifocals vs. Bifocals and Single Vision
Varifocal lenses offer an advantage over both single vision and bifocal lenses by providing a full spectrum of focus. Single vision lenses contain only one power, meaning a person with presbyopia would require separate pairs for distance and reading. This necessitates constantly swapping glasses throughout the day.
Bifocal lenses combine two different powers—distance and near—into one lens, eliminating the need to switch pairs. The key difference is the presence of a visible line separating the two distinct power segments. This line represents an abrupt jump in magnification, which can be visually jarring.
Bifocals lack the intermediate viewing zone that varifocals provide for arm’s length tasks like computer work. The wearer must choose between distance and near, with nothing in between, which poorly suits modern activities involving frequent intermediate focus. Varifocals offer the third power zone, allowing for a natural shift in focus across all distances without a distracting line or image jump.
Understanding the Adjustment Period
Switching to varifocal lenses requires a period of adaptation for the visual system. The brain and eyes must learn how to navigate the progressive corridor to find the correct focal point for different distances. This learning curve varies widely, ranging from a few days to about two weeks, though some people may take up to a month to feel comfortable.
During this initial phase, it is common to experience symptoms such as a slight wavy or “swimming” sensation when moving the head, mild dizziness, or difficulty judging depth perception. These feelings are primarily caused by the brain processing the peripheral distortion inherent in the lens design. Activities requiring precise depth judgment, like navigating stairs, may feel challenging at first.
A successful adjustment depends heavily on consistent use, and wearing the new varifocals immediately and continuously is highly recommended. It is important to resist the temptation to switch back to old glasses, as this confuses the brain and slows the adaptation process. A simple but effective technique is to turn the head to look directly at an object, ensuring the gaze passes through the clear central corridor, rather than just moving the eyes.
To find the near vision sweet spot, hold reading material and tilt the chin up or down until the text comes into sharp focus through the bottom section of the lens. This consistent practice helps the brain map the power zones onto the visual field. If adjustment difficulties persist beyond a few weeks, consult an eye care professional to verify the fit and prescription.