Adding bifocal power to existing single-vision lenses is generally not possible due to the fundamental way ophthalmic lenses are manufactured. Bifocals have two distinct optical powers: one for distance vision and a segment, typically in the lower portion, with added power for near vision tasks like reading. This near-vision segment, often called the “add power,” is a physically integrated part of the lens structure, not a coating or simple add-on. Since the lens material is permanently altered during initial production, you cannot chemically or physically modify a finished single-vision lens to introduce a new focal point without compromising its optical quality.
The Manufacturing Process of Multifocal Lenses
Bifocal power is incorporated into the lens from the beginning of the manufacturing process. In plastic lenses, the required curvature for the near-vision segment is achieved using a specialized mold into which the lens material is poured or cast. This creates a lens blank with the near segment’s curve already integrated, resulting in the visible dividing line on traditional bifocals.
For glass bifocals, the process involves fusing a smaller segment of glass with a different refractive index onto the main lens blank. This segment is melted and ground together with the main lens. The difference in the light-bending ability of the two glass materials creates the added magnifying power. Single-vision lenses are made to have a uniform power across the entire surface, and once the material is hardened, surfaced, and coated, its optical properties are fixed.
Attempting to grind, etch, or mold a new prescription segment into a finished lens would destroy the precise curvature and smoothness required for clear vision. Protective coatings, such as scratch resistance or anti-reflective layers, would also be compromised by any physical modification. The manufacturing complexity ensures the exact power accuracy and segment integration needed for a functional bifocal, which cannot be retroactively applied to a completed lens.
Practical Options for Existing Eyewear
The most common solution for gaining bifocal correction while keeping your current frames is to replace the existing single-vision lenses with new multifocal lenses. An optical professional can remove the old lenses and have new bifocal or progressive lenses cut to fit the exact shape and size of your current frame. This allows you to retain a favorite or expensive frame while updating your vision correction to include the required reading power.
A temporary alternative is to use stick-on bifocal segments. These are small, pliable, half-moon shaped lenses made of a polymer material that adhere to the inside surface of your existing single-vision lenses using only water. They create a small area of added magnification for close-up tasks, effectively converting any glasses, including sunglasses or safety glasses, into instant bifocals.
The stick-on segments are removable, reusable, and can be easily trimmed with scissors to fit the lens shape, making them a low-cost, quick-fix solution. These temporary lenses offer lower optical quality and precision compared to a custom-made, integrated bifocal. For those needing only slight reading magnification, another simple option is to use a separate pair of dedicated reading glasses. This allows you to wear your current distance glasses and switch between the two pairs as needed for near work.