5 Progressive Lens Numbers to Avoid Headaches & Blurry Vision

1. Sphere (SPH): Your Vision's Anchor
2. Cylinder (CYL): Fixing the "Warped Camera Lens"
3. Axis: The Compass for Your Astigmatism
4. ADD: Your Reading Lifesaver
5. Pupil Distance (PD): The Fit That Feels Invisible
Bonus: Segment Height—The Secret to Natural Movement

Progressive lenses are a game-changer for people with presbyopia (age-related vision loss that makes it hard to see close-up) or those needing multifocal correction. But did you know your prescription holds hidden secrets to how well your lenses work? Let’s break down the five critical numbers in a progressive lens prescription—and why each one matters for sharp, comfortable vision.

1. Sphere (SPH): Your Vision's Anchor

clear vision through sphere lenses

The sphere value tells us if you’re nearsighted or farsighted:

• Negative numbers (e.g., -2.00) mean nearsightedness (blurry distant vision, like struggling to read road signs).

• Positive numbers (e.g., +1.00) mean farsightedness (blurry near vision, like difficulty reading menus).

Why it matters:

This number powers the distance zone at the top of your progressive lens. For more details on how nearsightedness and farsightedness are diagnosed, visit the American Academy of Ophthalmology’s guide on refractive errors.

• Too weak: Distant objects stay fuzzy, forcing you to squint while driving.

• Too strong: Overcorrection can cause dizziness or “swim effect” when moving your head.

Special Tip:

Always update your SPH during annual eye exams. Even a small change (e.g., from -2.00 to -2.25) can significantly impact clarity.

2. Cylinder (CYL): Fixing the "Warped Camera Lens"

how astigmatism looks like

Astigmatism happens when your eye is shaped more like a football than a perfect sphere, causing blurred or warped vision at all distances. To learn how astigmatism is corrected, explore the American Optometric Association’s resource on astigmatism. The cylinder value (e.g., -0.75) corrects this by focusing light properly along a specific axis.

Why it matters:

Without proper CYL correction:

• Text on screens appears stretched or shadowed.

• Night driving becomes risky due to halo effects around headlights.

Special Tip:

Astigmatism may increase due to incorrect eye - using habits, especially when using electronic devices for long periods. If your astigmatism is increasing too rapidly, you should pay attention to taking good care of your eyes!

3. Axis: The Compass for Your Astigmatism

the conception pic of axis

The axis (a number between 1–180) tells us where the astigmatism occurs on your eye, like a “compass direction.” For example, an axis of 90 means the correction runs vertically (like a clock’s 12-to-6 position).

Why it matters:

A mismatch of even 10° can:

• Tilt horizontal lines (e.g., spreadsheet rows).

• Blur diagonal movements (e.g., watching a tennis match).

Special Tip:

Astigmatism Axis rarely changes, but always verify it if you get new frames or experience eye strain.

4. ADD: Your Reading Lifesaver

reading through the bottom of the lens where ADD power lies in

The ADD (addition power) is a positive number (e.g., +2.00) that adds magnification to the bottom of your lens for reading, cooking, or using your phone. It’s what turns a progressive lens into a “no-glasses-switching” solution for distance and near vision.

Why it matters:

• Too low: You’ll hold books farther away, straining your arms and eyes.

• Too high: Text looks unnaturally large, making tasks like sewing frustrating.

Special Tip:

Bifocals have a visible line—progressives hide the transition. Ask your optician about “office progressives” for computer-heavy work!

5. Pupil Distance (PD): The Fit That Feels Invisible

pupil distance (PD) measurement

PD is the distance between your pupils (measured in millimeters). It’s crucial because the lens’s “sweet spots” for distance, intermediate, and near vision must line up with where your eyes look.

Why it matters:

• Too narrow: Forces you to look sideways for the reading zone, causing neck pain.

• Too wide: Creates double vision in your peripheral sight.

Special Tip:

PD may not be directly shown on your prescription, but this value is crucial for customizing glasses. Please confirm your PD with your eye doctor or consult us for self-measurement methods.

Bonus: Segment Height—The Secret to Natural Movement

segment height illustration

Segment height measures where your pupil sits vertically in the lens. Progressive lenses have a “progressive channel” that gradually increases power from top to bottom. If this is misaligned:

• A too-low start might make you strain to look down for reading.

• A too-high start could blur your distance vision when you’re looking straight ahead.

Why it matters: It’s like custom-fitting a shoe—your lens should match how you naturally move your eyes. Whether you’re typing at a desk (intermediate vision) or bird-watching (distance), the right pupil height ensures each zone is exactly where you need it.

Special Tip:

Segment height usually doesn't appear on your prescription as it is data required only when processing lenses to fit different frames. If your prescription is correct but you experience blurred vision after receiving progressive glasses, it is likely that the segment height is incorrect. Please send us a photo of you wearing the glasses, and we will customize them for you again!