Bifocal Lenses: Pros, Cons, and Who Is a Candidate?

Bifocal lenses enable the eyeglass wearer to see clearly for both long-range sight and for up-close vision. People in their 40s are prime candidates for bifocals, particularly if they do not need help with their medium-range vision.

What Are Bifocal Lenses?

A bifocal lens corrects two refractive errors simultaneously (farsightedness and nearsightedness) by incorporating two different optic zones. With most prescriptions, the top zone provides distance focusing power, while the bottom lets you see close-up objects clearly.

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Who Is a Candidate for Bifocals?

Because bifocal lenses support two focusing distances, eye doctors recommend them for people with myopia (nearsightedness) and presbyopia (age-related farsightedness).

Many people experience a loss of the ability to focus on close-up objects in their early 40s. Poor near vision is a problem for people who have jobs that involve a lot of close-up work, such as reading or working at a computer.

Bifocal lenses could provide both the crisp near vision you need for close-up work and sufficient distance vision for driving. Myopic children can also benefit from bifocal lenses.

Types of Bifocals

When you compare various types of bifocal lenses, you may notice differences in shape or geometry of the lower, near-vision segments. Some notable design variations include:

• Flat top: The shape of the lower segment of the lens resembles a half-moon (also called the D-segment).
• Round segment: The lens has a round-shaped near-vision segment.
• Ribbon segment: The lower zone that you can look through for close-up work is narrow and rectangular.
• Executive: Also known as the Franklin style, or E style, the entire half of the executive bifocal lens provides near-vision.

Benefits

Left untreated, presbyopia can compromise your vision and take away your ability to work, read, drive or lead a more independent life. Treating the disorder with bifocal lenses provides various vision benefits, including:

• You get near-vision correction for reading or similar close-up activities.
• If you wear prescription distance-vision glasses, bifocals provide the same treatment to maintain your ability to see clear images from a distance, such as street signs.
• Correcting nearsightedness with bifocals may reduce eye strain because of reading.
• Wearing bifocal glasses may slow the progression of myopia by protecting the eye’s focusing muscles from excess stress.

How Are They Fitted?

Besides providing the correct lens power, bifocals should have a proper facial height so that the line separating the upper and lower focusing zones can do its job. A best-fit height ensures that your bifocal lenses address most of the vision needs accompanying your lifestyle and everyday routine.  

In a typical fitting session for a new pair of bifocal lenses, your eye doctor or optometrist may ask you to sit and put on the glasses. Maintain your natural body and head posture and place the glasses straight and in your most comfortable position.

The doctor will mark the fitting height starting at the top of your lower eyelid. When you stand and look at an object more than 20 feet away with your glasses on, you should be looking above the drawn fitting height.

When you look down, such as to read a book, you should be looking below the line.

Occupational Bifocals

Some professions require clear vision at different ranges of focus, which can change frequently. Occupational bifocals are designed with such applications in mind.

These bifocals solve vision requirements for a specific task, sport, or hobby. For example, car mechanics can wear the “Double-D” bifocal lenses for perfect near and intermediate vision when working from under a vehicle.

The inverted flat-top segment of the lens allows the lenses to provide wearers clear vision when they look up during close-up tasks. A flat-top section at the bottom of the lens would also provide near vision, with the middle zone supporting better distant vision.   

Anti-Reflective and Photochromic Bifocals

As with any type of prescription lenses, bifocals with specific treatments can provide extra eye protection besides treating presbyopia. Protective coatings include:

• Anti-glare protection: An anti-reflective coating protects you from eye strain by minimizing glare. Bifocal lenses with the protective layer provide clearer vision, including in dim light, making them ideal for night driving.
• Photochromic bifocals: These lenses provide sunlight protection with a tint that automatically gets darker or clearer based on ambient light. However, their “dynamic tint” may not function well in enclosed environments that don’t get the sun’s light rays, such as inside your car.   

Alternatives to Bifocals

Among the common alternatives to bifocal lenses that you may wear to correct presbyopia are:

• Monovision reading glasses: These lenses only provide near vision and are ideal for presbyopic patients with good distance vision.
• Trifocal lenses: Consider getting these multifocal lenses for clear vision at three focusing ranges: distance, intermediate, and close-up.
• Progressive lenses: These can be bifocal or trifocal, but they provide a smooth transition from distance to near vision and vice versa.

FAQs

What are bifocal lenses used for?

Bifocal lenses generally correct presbyopia or farsightedness that develops with aging. Wearing them enables you to see clear images of both near and distant objects.

Which is better: bifocal or progressive lenses?

Generally, both types of lenses function the same way in presbyopia treatment. However, the noticeable separation of focusing zones in bifocals can impact the visual experience. With progressive lenses, you get an inconspicuous transition of focusing distances. Implementing the seamless visual transitions comes with a compromise: less space for the focal areas on the lenses.

About 10 percent people cannot use progressive lenses because of their comparatively higher-distortion levels.

What are the disadvantages of bifocal lenses?

Some issues associated with bifocals include:

• Tendency of images to jump (shift location) during distance-vision to near-vision transition
• Image displacement (inconsistencies in distance between an image when you look through the distance segment of the lens vs. the near-vision segment)
• Bifocals do not usually provide intermediate vision in people with presbyopia

References

1. Presbyopia. (November 20, 2021). Mayo Clinic.

2. Guide to Bifocals and Multifocals. (June 1, 2020). Optometrists Network.

3. Fitting Height Considerations. (October 2011). 20/20 Mag.

4. Bifocal and Multifocal Contact Lenses for Presbyopia and Myopia Control. (March 27, 2020). Journal of Ophthalmology.

5. How to Choose Eyeglasses for Vision Correction. (February 25, 2020). American Academy of Ophthalmology.

6. Bifocal Add: Image Jump and Image Displacement. American Academy of Ophthalmology.