Contact lenses exist that correct both near and distance vision, fulfilling the core function of a bifocal lens. These specialized lenses address presbyopia, a common age-related condition that typically begins after age 40. Presbyopia occurs when the natural lens inside the eye becomes less flexible, making it difficult to focus on close objects. These lenses integrate multiple prescriptions into a single contact lens, allowing the wearer to see clearly at varying distances without needing reading glasses.
The contact lenses that correct for this condition are most often referred to as multifocal lenses in the eye care community. While the term “bifocal” is widely understood, it technically describes a lens with just two distinct power zones: one for distance and one for near vision. Multifocal is the more encompassing term, as modern designs frequently incorporate a gradual transition or multiple zones, including intermediate vision, much like progressive eyeglasses.
Clarifying the Terminology
While the function is similar to bifocal eyeglasses, the technology in contact lenses has largely evolved past a simple two-power division. A true bifocal contact lens features two separate and distinct optical powers within the lens, typically with a sharp boundary between the distance and near zones. This design can sometimes cause an abrupt jump in image clarity when the eye moves between the different fields of view. The modern multifocal design functions more like progressive lenses in glasses, offering a smooth, blended transition between far, intermediate, and near vision.
Understanding the Design
The two main design strategies used are Simultaneous Vision and Alternating Vision. Simultaneous vision designs are the most common and work by presenting both the near and distance prescriptions in front of the pupil at the same time.
Simultaneous Vision
Within the simultaneous vision category, two primary lens geometries exist: concentric ring and aspheric designs. Concentric lenses feature a bullseye pattern, alternating rings of distance and near power around the center of the lens. Aspheric designs blend the different powers across the lens surface with no distinct lines, similar to a progressive spectacle lens. In both simultaneous designs, the brain learns to filter out the slightly blurred image from the power zone not needed, focusing only on the clearest image.
Alternating Vision
A less common design is the Alternating Vision or translating lens, which functions more like traditional bifocal glasses. These lenses are made of a rigid gas permeable (RGP) material and are designed to physically move or “translate” on the eye. When the wearer looks down to read, the lower eyelid catches the bottom edge of the lens, pushing the lens up so the pupil centers over the near-vision segment. This design provides a crisp view at both near and far distances, but requires precise fitting and consistent lens positioning.
Practical Considerations for Wearers
Adopting multifocal contact lenses requires a specialized fitting process that is more involved than a standard single-vision lens fitting. The eye care professional must select a lens design and power combination that balances the patient’s needs for distance, intermediate, and near vision, often requiring trial lenses and multiple appointments. Achieving the best outcome usually involves a compromise, as optimizing one distance may slightly reduce sharpness at another.
A period of neuro-adaptation, or adjustment, is necessary for the brain to learn how to process the simultaneous images presented by the lenses. It usually takes a wearer between one to two weeks for their brain to fully adjust to the new way of seeing. During this initial phase, some individuals may experience minor side effects, such as slight blurriness, halos, and glare, particularly when driving at night.
Consistent wear is important during the adaptation period to allow the brain to fully integrate the new visual input. Open communication with the eye care professional is also important to fine-tune the prescription. If initial blurriness or discomfort persists beyond the typical adjustment window, a change in lens design or power may be necessary to achieve satisfactory vision.