Aren't all lenses the same?
Two lenses. The same prescription throughout. Roughly 50% apart in price. Drag them and see what the money buys.
Press the image and drag sideways to change the prescription. As the prescription increases, the lens thickens at a steady rate.
The same range of prescriptions in a denser material. The lens stays substantially thinner at every step.
Rotate the lens and watch the words distort, particularly at the periphery — and even when the lens is perpendicular to the line of sight.
The same prescription in a different design. Less peripheral distortion through the rotation, and a cleaner view straight through the lens.
Every progressive lens has blurry sides. Here is why.
A progressive lens is a staircase. Each step down the lens adds a little power, from distance at the top to reading at the bottom. A bifocal makes the trip in one big step, a trifocal in two, and a progressive in hundreds of tiny steps, so small that the lines disappear.
Look at the edges of the six-step lens. Each step is a slice of a slightly smaller ball, so the steps line up only down the middle and drift apart toward the sides. Smooth them into a progressive and that mismatch becomes a twist in the surface, which the eye sees as blur.
Stair builders know the problem from every staircase that turns a corner. Along the walking line each step is exactly the right depth. Toward the inside the steps get shallower, toward the outside they get deeper, and the farther from the walking line, the worse it gets. The corridor down the middle of a progressive is its walking line.
No design removes the mismatch. The inside of a turn is always a shorter path, and in 1963 the mathematician Günter Minkwitz proved the same kind of rule for lenses. What designers can do is share it out: keep the middle path perfect and move the blur to where it bothers you least.
Every progressive follows the same rules. What changes with price is how much of the lens is calculated for you, and how it is made.
Your prescription, your frame and how it sits on your face, built into the lens surface itself.
Matched to the frame's depth, so the reading zone is not cut off in a shallow frame.
Cut point by point by computer-controlled machines, rather than moulded in bulk.
Years of design and wearer testing decide how mild it is and where it sits.
The difference is largest with stronger prescriptions, higher reading powers, and shallow or wrapped frames. To see the maths behind every picture, in 3D, open Building a Progressive Lens in our Visual Systems Lab.
A redo is a pair of glasses remade because it was not working for the patient. At many opticals one pair in eight or nine comes back. Ours is under three in a hundred, and that is not a claim about the lenses alone — five things account for it, further down this page.
The right lenses, for the right frame, for the right patient.
Selecting lenses is not simply a matter of matching a prescription. Lens index, curvature, optical centre placement and coatings each change how a prescription performs on a face, in a frame, at the distances that person actually works at. Our opticians work with our doctors on every pair.
Anyone should be free to buy glasses wherever they like — we would rather the decision were an informed one. Material density changes the thickness on your face. Lens design changes how much of the lens you can actually see through. Neither is visible in a product photograph, and neither can be measured from a prescription typed into a form. What an order form cannot capture is where your pupils sit behind the frame you chose.
A correct prescription can still feel wrong if the lenses were not chosen and fitted with care. Before we order anything, we work through four things.
How you use your eyes at work, and at what distances you use them most of the day.
Screen hours, driving, time outdoors and sport — each pulls the lens design in a different direction.
How the frame you chose actually sits on your face, which sets where the optics have to land.
What you have worn before, what worked, and what you never adapted to.
What keeps it under 3%.
Lenses do not exist in isolation. A prescription that performs in one frame can underperform in another if the shape, size or wrap is not compatible. So we analyse frame geometry before selecting a lens, measure optical centres and pupillary distance with precision instruments, and adjust the frame to your features before you leave. Done properly, there is no period of getting used to your glasses.
We are not tied to one brand, because no single lens suits every patient. Nikon for optical clarity and coatings, Hoya for lightweight comfort and progressive performance, and access to lens labs worldwide for everything either one does not cover.
