Progressive lenses and bifocals both correct refractive errors, but they differ in design and functionality. This overview will provide information on how to choose between the two styles of glasses during your next trip to the optical shop.
Progressive Lenses vs. Bifocals
People with a single corrective error, such as myopia (the inability to see objects clearly at a distance, also known as nearsightedness) or hyperopia (the inability to see objects clearly up close, also known as farsightedness) can benefit from glasses or contacts to correct their vision. However, whenever you combine multiple refractive errors, such as myopia and the development of presbyopia as you age, more advanced lenses are needed to see both near and far.
Bifocals and progressive lenses are two types of eyeglass lenses used to correct more than one type of refractive error. In general, bifocals offer distinct vision fields separated by a segmented line, whereas progressive lenses have seamless transitions for a less distracting visual experience.
Bifocals
Bifocal lenses contain two different magnification levels separated by a visible line.
- Distinct vision fields: Bifocals provide two types of vision correction, typically distance and near vision. The lower portion addresses issues with reading, while the top portion helps to see objects clearly at a distance.
- Visible segment lines: Unlike progressives, bifocals have visible segment lines that separate the different power zones on the lens.
- Limited zones: Bifocals offer just two vision zones, with the result that there is no smooth transition between the visual distances.
Types of Bifocal Lenses
- Flat-top bifocal lenses: Also known as straight-top bifocals or D-segmented bifocals, the bottom segment is in the shape of a flat-top “D” to assist with reading tasks.
- Round segmented bifocal lenses: Unlike traditional bifocals that have a distinct horizontal line separating near and distance vision areas, round segmented bifocals feature a rounded segment at the bottom of the lens to assist with close up tasks.
Progressive Lenses
Progressive lenses, or multifocal lenses, provide continuous vision correction without the lines seen in bifocals. The top of the lens helps you see objects at a distance, the middle of the lens allows you to focus on intermediate objects, and the bottom of the lens helps you see objects up close.
- Seamless transition: Progressive lenses provide a seamless transition between near, intermediate, and distance without visible lines.
- Eliminates vision jump: Progressive lenses solve the issue of “image jump” seen with bifocal lenses by smoothing out transitioning powers, preventing image distortion.
- Advanced technology: Progressive lenses use cutting-edge technology to provide a broader clear vision area, improving comfort and functionality.
- Wider zone of clear vision: Progressive lenses provide clear vision across a wider range of distances compared to bifocals, including intermediate distances that are used for computer work.
Types of Progressive Lenses
- Standard progressive lenses: These lenses are designed based on standard parameters for field of view and where it is located in the lens. Typically they require larger frames and require more adjustment from the wearer to find the optimum viewing area.
- Premium progressive lenses: These lenses offer a wider viewing area with smoother transition than standard progressive lenses. They can be customized based on an individual’s eye anatomy, prescription, and frame. This offers less distortion and allows for smaller frames.
- Short corridor progressive lenses: These lenses are made for smaller frames and provide quicker access to the reading area compared to traditional progressive lenses.
- Computer progressive lenses: These lenses prioritize the intermediate viewing zone, which helps tasks such as viewing a computer.
What Lenses Should You Choose?
It can be difficult to choose between progressive lenses and bifocals. Ultimately, it comes down to your personal preference and what suits your needs.
While some individuals may find bifocal lines intrusive in their field of vision, others are unaffected by them. Progressive lenses have smaller focused areas compared to bifocals, as the transition zones require additional space. However, progressive lenses can introduce more distortion than alternative lens types, potentially posing challenges for certain wearers.
Progressive lenses are ideal for people who need vision correction at all distances. Bifocals, on the other hand, work well for people with myopia who develop the need for assistance seeing images up close as they age.
Bifocals are typically more affordable since progressive lenses use advanced technology.
Factors to Consider When Buying Progressives
Corridor length (the vertical area on the lens where the power changes gradually from distance to near vision) is important to know when buying progressive lenses. Variances in corridor length affect the size and width of the different focal zones within the lens.
In simpler terms, when the part of the lens for reading and computer use is taller, the area where your vision shifts smoothly from far away to up close (the corridor) is longer. On the other hand, if that reading part is shorter, the corridor in the lens may also be shorter.
Additionally, a lens with a shorter transition area (corridor) might work well for reading up close but could feel limited when you need to see things at in between distances, like a computer screen.
Regular progressive lenses usually need about 22mm of frame depth beneath the center of the lens to make sure the transition area in the lens works well. This helps line up your eyes with the right parts of the lens for clear vision at different distances.
To ensure comfortable vision with progressive lenses, it is recommended to have a minimum lens height of 28mm. Larger lenses offer better coverage for prescriptions, enhancing the experience. Aim for 32mm or more for optimal results when choosing frame sizes for progressive lenses.
