Progressive Lenses Differences

Progressive lenses are multi-focal lenses that replace traditional bifocal or trifocal lined lenses. Progressive lenses use blended focal fields for optimum vision correction without the distraction of lines across the lens. Progressive lenses differ in the lens material, clarity, and field of view. Progressive lenses can be combined with technologies, such as adaptive coatings that change color in sunlight.

Materials

• The most common materials for progressive lenses are glass, regular plastic, high-index plastic and polycarbonate. Glass lenses are heavy with some prescriptions. Common plastic weighs less than glass, but can scratch easily. High-index plastic is used for very thin lenses where excess weight is an issue. Polycarbonate is both impact and scratch resistant, but has less optical clarity than the other materials.

Viewing Corridor

• Progressive lenses contain a viewing corridor down the center of each lens. The corridor is ground for the customer's prescription, then the prescriptions are blended to remove the lines seen in regular bifocal or trifocal lenses. The width of the optimum viewing corridor is a major difference in lens price. A wider viewing corridor provides less distortion at the edges. A common effect of progressive lenses, called "swimming," is also reduced by widening the viewing corridor. All progressive lenses have distortion in the outer viewing areas of the lens. Wearers should turn their head and look through the optimum viewing corridor to prevent distortion, rather than relying on peripheral vision.

Lens Size

• Early progressive lenses were larger than conventional lenses due to the technology at the time for blending prescriptions. Smaller lenses are now made using digital lens processing. Digital processing creates a more precise viewing area and optimizes the viewing corridor for smaller frames. A larger lens will result in a larger viewing area; customers having problems adapting to progressive lenses should try larger lens sizes.

Advantages of Progressive Lenses Over Standard Lenses

• Progressive lenses permit a "no-line" design for multi-focal lenses. Wearers do not have to carry multiple pairs of glasses for distance viewing and reading. "Image jump," a common problem with lined bifocals, is eliminated. Sun-darkening lenses or clip-on sunglasses may eliminate the need for a separate sunglasses prescription.