Bifocal vs progressive
Two answers to the same problem — one pair of glasses that works at more than one distance. They fail in opposite directions, and which failure you can live with is the whole decision.
The short answer. A progressive if you need arm's length as well as near and far, or if a visible line matters to you. A bifocal if you want a wide undistorted reading area with no adaptation, if your frame is too shallow for a progressive (under about 34 mm deep), or if cost is the constraint. Neither is the better lens; they are different trades.
The question this page answers: should I get bifocals or varifocals?
What each one actually is
A lined bifocal is two lenses in one piece of material. The upper part carries your distance prescription and the lower part carries it plus the reading add, with a visible boundary — the segment line — between them. Nothing is blended. Each region is as optically clean as a single-vision lens, and the full width of the lens is usable in both.
A progressive, or varifocal, blends the two powers continuously down a corridor running from the fitting cross to the reading area. There is no line and no jump, and at every height down the corridor there is an intermediate power — which is why a progressive works at arm's length and a bifocal does not.
That blending has a cost, and it is unavoidable rather than a manufacturing limitation. A surface that changes power smoothly down the middle must have unwanted astigmatism either side of that middle; the mathematics does not permit otherwise. Those are the soft regions at the lower corners of every progressive lens, and they are what produces the swimming sensation when a new wearer turns their head.
The trade in one line. A bifocal gives you two clean, wide regions and a line between them with nothing in the middle distance. A progressive gives you every distance and no line, at the cost of narrow usable regions and distorted periphery. There is no design that gives you both, because the geometry forbids it.
Where each one wins
| Lined bifocal | Progressive | |
|---|---|---|
| Middle distance | Not corrected | Corrected, continuously |
| Reading width | Full lens width | 11–18 mm by design |
| Peripheral distortion | None | Present at the lower corners |
| Visible line | Yes | No |
| Image jump at the boundary | Yes, permanent | None |
| Adaptation | Days, partial | One to three weeks, usually complete |
| Minimum fitting height | About 14 mm | 11–20 mm by design |
| Cost | Lower | Higher |
The frame decides more than you expect
The measurement that governs this choice is the fitting height: the vertical distance from the centre of your pupil down to the inside bottom edge of the frame, once the frame is on your face. It is not marked anywhere on a frame, and it cannot be worked out from the three numbers stamped inside the temple — those give the width, bridge and temple length, and say nothing about depth.
Every progressive design has a minimum fitting height published by its manufacturer, below which the reading area simply does not fit inside the lens. Below is roughly what each frame depth allows, assuming the pupil sits a little above the vertical middle of the lens, which is where it usually sits.
| Lens depth | Fitting height | Ultra-short | Short | Standard | Long | Bifocal |
|---|---|---|---|---|---|---|
| 28 mm | 16 mm | Fits | Fits | No | No | Fits |
| 34 mm | 19 mm | Fits | Fits | Fits | No | Fits |
| 40 mm | 22 mm | Fits | Fits | Fits | Fits | Fits |
| 46 mm | 25 mm | Fits | Fits | Fits | Fits | Fits |
The pattern in that table is the practical heart of this decision. A shallow modern frame — the wide, short rectangles that have been fashionable for a decade — will take a bifocal and may take nothing better than an ultra-short progressive, which is a poor lens. A deep frame takes anything, including the long-corridor designs with the calmest optics. If you have settled on a frame before thinking about lenses, you have already made part of this choice.
This is the single most useful thing to know before walking into a shop: take the frame you like and have its depth measured before you discuss lens types. A dispenser who fits a standard progressive into a frame that cannot hold it produces glasses whose reading area starts below the bottom rim, and the wearer is told they failed to adapt.
Who is better served by a bifocal
Bifocals have an undeserved reputation as the old-fashioned option, and there are several situations where they are straightforwardly the better lens.
- Anyone who reads for hours. A standard progressive gives you about 15 mm of usable reading width; a bifocal gives you the whole lens. Over a long book that difference is the difference between holding your head still and moving it along every line.
- Shallow frames. About 14 mm of fitting height is enough, against 17 mm for a standard progressive.
- People who have tried progressives and could not adapt. A minority never do, and being told to persevere a third time is not useful advice.
- High add powers. The stronger the add, the more unwanted astigmatism a progressive must generate to blend it. Above about +2.50 the soft regions get noticeably worse, while a bifocal is unaffected.
- Cost. A plain reason, and a good one.
Who is better served by a progressive
- Anyone who works at a screen. A monitor sits at roughly arm's length, which is exactly the distance a bifocal does not correct. This is the commonest reason people switch, and it is decisive.
- Anyone who moves between distances constantly — driving, cooking, teaching, anything where the next thing you look at is at an unpredictable distance.
- Anyone bothered by the line, which is a legitimate preference and not vanity: the line is visible to other people and it sits in your own peripheral vision.
- Anyone who has to go up and down stairs often. A bifocal's image jump is at its most unpleasant on a stair edge; a progressive has none.
The third option nobody offers
Two pairs. A single-vision distance pair and a single-vision reading pair, or a distance pair and a dedicated intermediate pair for a desk, each with the full lens width available and no compromise anywhere. It is often cheaper than one good progressive, and for someone who sits at the same desk all day it is a better answer than either lens on this page.
It is rarely suggested, partly because carrying two pairs is a nuisance and partly because a shop sells one pair of progressives more profitably than two pairs of single vision. If your complaint is specifically that reading at a desk is uncomfortable, ask about a dedicated office or occupational lens — a design with a very wide intermediate and near area and no useful distance zone, which is a far better desk lens than any general-purpose progressive.
Measure before you choose
The progressive lens fit tool takes your frame's lens depth and tells you which corridor designs will fit, how much reading width each would give you, and when the honest answer is that this frame cannot take a progressive worth wearing. It is the measurement this entire decision turns on, and it takes about a minute with a ruler.
Minimum fitting heights are the published figures for each class of design; individual products vary and your dispenser's own chart is authoritative. Nothing here is a substitute for a sight test or for an optician's advice about your own eyes.
Questions people ask
- Are progressives better than bifocals?
- Not categorically — they solve different problems. Progressives give you continuous focus at every distance including arm's length, which bifocals do not, and no visible line. Bifocals give you a wide, undistorted reading area with no adaptation period and no peripheral swim. Someone who spends all day at a fixed-distance screen is often better served by a bifocal or a dedicated pair.
- Why do progressives make me feel dizzy at first?
- The power changes gradually down the lens, and that gradient produces unwanted astigmatism either side of the corridor — the "swim" people describe when they turn their head. It is a geometric consequence of blending two powers in one surface, not a fault, and most people stop noticing within two weeks. A longer corridor spreads the change over more millimetres and reduces it.
- Is there an adaptation period for bifocals?
- Much less, but not none. The image jumps as your eye crosses the segment line, which is disconcerting on stairs and kerbs for the first few days. Unlike progressive swim, it does not go away — you learn to drop your chin rather than your eyes.
- Can I get progressives in any frame?
- No, and this is the most common disappointment at a counter. A standard corridor needs 17 mm between the pupil centre and the bottom rim, which means a lens about 34 mm deep. Many fashionable frames are shallower than that. A lined bifocal needs about 14 mm, so it fits frames a progressive will not.
- Which is cheaper?
- Bifocals, usually by a wide margin, because the surface is simpler to make. The gap has narrowed as progressive manufacturing has become routine, but a lined bifocal remains the cheaper way to get two powers in one lens.