Presbyopia is the natural decline in the eye’s ability to focus on close objects, typically starting in the early to mid-40s as the lens stiffens. Holding reading material farther away is a common sign that near-vision correction is needed. Modern contact lens technology offers solutions that allow people to maintain clear vision at all distances without relying on reading glasses. Contact lenses are available that incorporate multiple prescriptions to address this age-related focusing challenge.
Bifocal Versus Multifocal Lenses
The terms “bifocal” and “multifocal” describe different optical designs, though they are often used interchangeably. A true bifocal contact lens contains two distinct power zones: one for distance vision and a separate one for near vision. This design mirrors traditional bifocal eyeglasses by having only two focal points.
Multifocal lenses function more like progressive eyeglasses, providing a gradual transition in power between distance, intermediate, and near vision. This progressive design means the lens contains a range of powers rather than just two segments. Most advanced lenses available today are technically multifocal in nature.
Optical Design Mechanisms
Multifocal contact lenses use sophisticated designs to ensure clear vision at varying distances. These designs fall into two primary categories: simultaneous vision and alternating vision systems.
Simultaneous vision lenses are the most common type. They are designed so that both the near and distance prescriptions are positioned in front of the pupil simultaneously. The brain then learns to preferentially select the clear image and ignore the blurred one, depending on the object being viewed.
Concentric and Aspheric Designs
Simultaneous designs utilize either a concentric or an aspheric structure. Concentric lenses feature alternating rings of distance and near power, often with the distance or near correction located centrally. Aspheric designs blend the different powers across the lens surface, creating a smooth, progressive change similar to a gradient. These blended zones ensure a continuous range of focus, including intermediate vision, without any visible lines on the lens.
The alternating, or translating, vision system is most often found in rigid gas permeable (RGP) lenses. This design is segmented, much like traditional bifocal glasses, with a distinct distance zone on the top and a near zone on the bottom. When the eye looks down to read, the lower eyelid engages the bottom edge of the lens, causing it to shift or “translate” upwards. This movement places the near-vision segment directly over the pupil for close-up tasks.
Alternative Vision Correction Options
While multifocal lenses offer a comprehensive solution, they do not provide perfect vision for every individual, and other options exist for presbyopia correction. One popular alternative is monovision, which uses standard single-vision contact lenses. In this fitting, the dominant eye is corrected for distance vision, while the non-dominant eye is corrected for near vision. The brain adapts to use the clearer image from each eye, offering a functional compromise. This approach can result in some reduction of depth perception and may not be suitable for tasks requiring acute binocular vision.
A variation called modified monovision pairs a single-vision lens for distance in one eye with a multifocal lens in the other eye to enhance intermediate and near performance. Another simple option is to wear distance-only contact lenses and rely on over-the-counter reading glasses for close-up work.
Finding the optimal solution for presbyopia requires professional guidance. An eye care specialist must consider factors like pupil size, tear film quality, and lifestyle needs when recommending a lens design. Due to the intricate nature of multifocal correction, a fitting process involving trial lenses and multiple adjustments is necessary to achieve the best visual outcome.