Progressive Lenses: A Comprehensive Guide for Progressive Glasses

Progressive lenses are multifocal lenses designed to provide clear vision at all distances in one pair of glasses. Unlike single-vision lenses – which have one constant prescription across the entire lens – progressives have a continuously changing power from top to bottom. The top of the lens is set for distance vision, the middle for intermediate (computer) viewing, and the bottom for near reading. Because they blend smoothly between powers with no visible line, progressives look like regular single-vision glasses. By contrast, traditional bifocals/trifocals have distinct segments and a visible line separating the distance and near zones.

Many wearers prefer progressives because they eliminate the need to switch between multiple pairs of glasses, offering a seamless, natural view of the world at far, intermediate, and near distances.

Key Differences:

• Single-Vision: one prescription (far OR near) across the entire lens. Ideal for simple myopia or hyperopia.
• Bifocals/Trifocals: two or three distinct powers divided by a visible line. The line is easily seen and separates distance from near vision.
• Progressive Lenses: no line, three vision zones fused by a smooth gradient. Distance vision is at the top, near vision at the bottom, with an intermediate zone in between.

Decoding Your Progressive Lens Prescription

• Add Power (ADD): Extra magnification for near tasks. Always a positive value, added to the distance prescription to provide clear reading vision.
• Pupillary Distance (PD): Distance between the centers of your pupils. Ensures each lens aligns with your line of sight.
• Fitting Height: Vertical distance from the frame to your pupil center. Used to place progressive zones correctly.
• Corridor Length: Zone where power transitions from distance to near. Affects intermediate viewing width and distortion.

What Are Back-Surface Progressive Lenses?

Back-surface (or internal) progressive lenses place the progressive corridor – the area that transitions from distance to near power – on the inner side of the lens, closer to the eye. The outer surface remains a regular spherical or aspherical curve.

Design Characteristics:

• Internal Progressive Surface: All vision zones (distance, intermediate, near) are shaped into the inner surface. The outer surface stays uniform.
• Smooth External Surface: Since the gradient isn’t on the outer surface, it’s easier to maintain and more scratch-resistant.
• Precision Manufacturing: Requires advanced free-form or CNC surface cutting to ensure micro-level accuracy.

Main Advantages:

• More Stable Vision: A smoother outer surface provides uninterrupted vision when shifting between zones.
• Cleaner Aesthetics: No visible lines or distortion on the outer surface, even from an angle.
• Better Durability: The progressive zone is protected from exposure, making the lens more resistant to scratches and smudges.
• Faster Adaptation: Uniform outer surface allows quicker adjustment, reducing discomfort or nausea for first-time wearers.
• Custom Optimization: Advanced free-form shaping can tailor lenses to facial anatomy, pupillary height, head position, and frame geometry.

Comparison with Traditional and Dual-Surface Progressives:

Ideal Users:

• First-Time Wearers: Easier adaptation makes them ideal for beginners.
• Aesthetically Conscious: No visible transition lines, great for large transparent frames.
• Professionals: Those who switch frequently between near and far (teachers, designers, drivers).
• Outdoor Workers: Enhanced durability against dust, debris, and environmental exposure.

Recommended Index by Prescription:

• 1.56 Index: For mild prescriptions (≤ ±3.00D, ADD ≤ +2.00D)
• 1.60 Index: Balanced option (≤ ±4.50D, ADD ≤ +2.50D)
• 1.67 Index: Moderate to high myopia (−3.00 ~ −6.00D, ADD +1.25 ~ +3.00D)
• 1.74 Index: Ultra-high prescriptions (−6.00D or above); requires full-rim frames

Fitting & Measurement Tips:

• Precise Measurements: Back-surface progressives require accurate pupil height, PD, vertex distance, and frame tilt.
• Frame Selection: Medium or large frames (width ≥ 48mm) ensure enough reading zone area.
• Personalized Free-Form: Tailored to facial shape and gaze patterns for optimal performance.
• Adaptation Period: Usually within 3–7 days. Fine adjustments may be needed post-fitting.

In summary, back-surface progressives place the full progressive power gradient on the inner lens surface. This delivers cleaner aesthetics, better durability, faster adaptation, and more personalized comfort – making them an excellent choice for modern multifocal wearers.