Short vs standard progressive corridors
Every progressive lens has a corridor — the channel where the power climbs from distance to reading. Its length is set by the frame, not by you, and it decides how good the lens can be.
The short answer. A standard corridor needs about 30 mm of lens depth and gives you roughly 15 mm of reading width. A short corridor fits in about 24 mm and costs you about 27% of that width plus noticeably more peripheral swim. If you can find a frame deep enough for a standard design, take it.
The question this page answers: will a progressive lens fit in the frame I like?
What a corridor is
A progressive lens has your distance prescription at the top and your distance prescription plus the reading add at the bottom. Between them the power has to climb continuously, and the vertical channel where that happens is the corridor. Its length — how many millimetres the climb takes — is the single number that determines what the lens feels like.
Blending two powers across one surface has an unavoidable cost. The mathematics of curved surfaces means that a surface whose power changes smoothly down the middle must carry unwanted astigmatism either side of that middle. Those are the soft, swimming regions at the lower corners of every progressive, and no manufacturer has ever eliminated them because they cannot be eliminated.
What a designer can do is spread the change over more millimetres. A gentler gradient produces less unwanted astigmatism and a wider usable channel. That is the whole trade:
Longer corridor — a gentler power change, so a wider reading area and a calmer periphery. Needs a deeper frame.
Shorter corridor — a steeper power change, so a narrower reading area and more swim. Fits a shallower frame.
The four classes
| Design | Corridor | Min fitting height | Min lens depth | Reading width |
|---|---|---|---|---|
| Ultra-short corridor | 11 mm | 11 mm | 18 mm | 8 mm |
| Short corridor | 13 mm | 14 mm | 24 mm | 11 mm |
| Standard corridor | 16 mm | 17 mm | 30 mm | 15 mm |
| Long corridor | 18 mm | 20 mm | 36 mm | 18 mm |
Read the last column carefully, because it is the one that gets felt rather than discussed. Moving from a standard corridor to a short one costs about 27% of the usable reading width. In practice that is the difference between holding a book still and moving your head along each line — and the people most likely to be sold a short corridor are the people whose frame choice has already been made.
Fitting height is the number, not lens depth
The measurement a lab works to is the fitting height: the vertical distance from the centre of your pupil down to the inside bottom edge of the frame, measured with the frame adjusted and sitting on your face. It is not the lens depth, and it is not marked on any frame.
The two are related because the pupil usually sits a little above the vertical middle of the lens, so a given lens depth implies a fitting height — but only approximately, and the approximation breaks for anyone whose frame sits unusually high or low on their face. Below is that approximation, which is also what our fit tool uses before you override it with a real measurement.
| Lens depth | Est. fitting height | Ultra-short | Short | Standard | Long |
|---|---|---|---|---|---|
| 26 mm | 15 mm | Fits | Fits | — | — |
| 30 mm | 17 mm | Fits | Fits | Fits | — |
| 34 mm | 19 mm | Fits | Fits | Fits | — |
| 38 mm | 21 mm | Fits | Fits | Fits | Fits |
| 42 mm | 23 mm | Fits | Fits | Fits | Fits |
| 46 mm | 25 mm | Fits | Fits | Fits | Fits |
A worked example: the shallow frame problem
Take a 30 mm lens depth — unremarkable for a modern wide rectangular front, and the kind of frame a great many people pick first. That gives a fitting height of about 17 mm.
| Design | Verdict | What that means |
|---|---|---|
| Ultra-short corridor | Room to spare | Exists so that shallow frames can take a progressive at all. The power climbs over eleven millimetres, which is abrupt — expect noticeable swim at the edges and a narrow reading channel. A last resort rather than a choice. |
| Short corridor | Fits | The workable answer for a modern shallow frame. Most people adapt to it, though the reading area is meaningfully narrower than a standard design and you will move your head more. |
| Standard corridor | Marginal | The design most progressives have historically been. A good balance: enough corridor length for a gentle power change, enough reading area to hold a book still. |
| Long corridor | Will not fit | The widest and calmest optics available, and it needs a deep frame to hold them. Worth seeking out if you read for hours or have a high add. |
This is the situation that produces most unhappy progressive wearers. The frame will only hold the shortest designs; the dispenser fits one; the wearer finds the reading area narrow and the periphery unsettled, persists for a month, and concludes that progressives do not suit them. They suit them fine. The frame was the problem, and it was chosen before anyone mentioned lenses.
The practical sequence, in the order that avoids this: decide you want a progressive, find out what corridor length you want, then choose from the frames deep enough to hold it. Doing it the other way round means the frame silently makes the lens decision for you.
When a short corridor is the right answer
It genuinely is, sometimes, and the case is worth making properly.
- When the frame is fixed — a frame the wearer loves, or an existing one being reglazed. A short corridor in the frame you will actually wear beats a standard corridor in one left in a drawer.
- For a low add. Under about +1.50 the power climb is small, so a steeper gradient produces less unwanted astigmatism than it would at a high add. Early presbyopes in shallow frames do well on short designs.
- For an experienced wearer. Someone who has worn progressives for a decade adapts to a shorter corridor far more readily than a first-time wearer, who is learning the whole lens at once.
- When the alternative is no progressive. An ultra-short design in a shallow frame is a poor lens, and it is better than a lens whose reading area starts below the rim.
The reverse case is just as clear. A first-time wearer, a high add, long periods of reading, or any combination of those, points to the longest corridor the frame can hold — and to choosing the frame accordingly.
What else affects how it feels
- Add power. The corridor has to climb further on a +2.50 add than a +1.00, over the same millimetres, so every distortion is proportionally worse. High adds want long corridors.
- Fitting accuracy. A fitting height measured two millimetres low puts the whole corridor low on your face, so you tip your head back to read. This is a dispensing error rather than a lens fault and it is fixable by remaking the lens.
- Frame wrap and pantoscopic tilt. How much the front curves around your face and how far it tilts both change where your line of sight crosses the lens. A good dispenser measures these; a cheap online order assumes them.
- Free-form surfacing. Modern lenses can be surfaced to your specific frame and fitting measurements rather than cut from a stock design. It genuinely helps, and it is the upsell on this page most likely to be worth the money.
Measure your frame first
The progressive lens fit tool takes your frame's lens depth, or your measured fitting height if you have one, and tells you which designs will fit, how much reading width each gives, and when the honest answer is that this frame cannot hold a progressive worth wearing. It takes a minute with a ruler, and it is much better done before you buy the frame than after.
Minimum fitting heights and reading widths are indicative figures for each class of design. Individual products vary and your dispenser's own fitting chart is authoritative. This is not a substitute for a professional dispensing appointment, which measures things a web page cannot.
Questions people ask
- What is a progressive lens corridor?
- The vertical channel down the lens where the power climbs from your distance prescription to your full reading add. Its length is how many millimetres that climb takes: 11 mm on an ultra-short design, 18 mm on a long one. Shorter means a steeper climb and more distortion either side.
- What fitting height do I need for progressives?
- It depends on the design. A standard corridor needs 17 mm from pupil centre to the bottom rim, a short corridor 14 mm, and the ultra-short designs 11 mm. In lens depth that is roughly 30 mm, 24 mm and 18 mm respectively.
- Are short corridor progressives bad?
- Not bad, but genuinely compromised. A short corridor gives you about 11 mm of usable reading width against a standard design's 15 — roughly 27% narrower — and the steeper power change means more peripheral swim. For a frame that cannot take anything longer it is a reasonable answer. As a default it is not.
- Can I put progressives in any frame I like?
- No, and this is the commonest disappointment at a dispensing counter. Many fashionable frames are too shallow to hold a progressive worth wearing. Measure the frame's lens depth before you fall in love with it.
- Why does my new progressive feel worse than my old one?
- A common cause is a shallower frame forcing a shorter corridor. The prescription is identical and the lens is doing the same job over fewer millimetres, which produces a steeper gradient and more distortion. Another is a fitting height measured incorrectly, which puts the corridor in the wrong place on your face.