Glasses can look deceptively simple.
Choose a frame, add your prescription and you are done — or at least that is how it can appear.
In reality, people have a huge number of questions about their glasses. What does CYL mean? Do you really need thinner lenses? Are varifocals difficult to wear? Do blue light glasses actually work? And can you safely order prescription glasses online?
These are some of the questions people regularly search for when trying to make sense of their prescription, frames and lenses.
So rather than giving you the sales answer, here are 15 straightforward answers from a UK Registered Dispensing Optician.
1. Can I buy prescription glasses online safely?
Yes — but the quality of the process matters.
Ordering prescription glasses online can work extremely well, particularly for straightforward prescriptions, provided the correct prescription and measurements are used and the chosen frame is suitable.
The important thing is not simply whether the glasses were bought online or in a practice. It is whether the optical information used to make them is correct.
Things such as your pupillary distance, prescription, frame dimensions and lens choice can all affect the finished result.
Stronger prescriptions and varifocals deserve even more consideration because frame fit and lens positioning become increasingly important.
At Burghley & Co, prescription orders are professionally reviewed before glazing. If something does not look right, we would rather contact you before making the lenses than simply manufacture what has been entered online.
Read our complete guide to buying prescription glasses online →
2. How do I read my glasses prescription?
A spectacle prescription can look confusing because it contains several abbreviated terms.
The most common are:
- SPH — Sphere. The main amount of long- or short-sighted correction.
- CYL — Cylinder. The amount of correction required for astigmatism.
- AXIS — The orientation of the cylinder correction, measured between 0 and 180 degrees.
- ADD — Additional near power, commonly used for reading, bifocal or varifocal prescriptions.
- PRISM — A less common correction used where the eyes need help working together or aligning an image.
A plus prescription does not automatically mean reading glasses and a minus prescription does not tell you everything about someone's vision. The entire prescription needs to be considered together.
If you are ordering glasses and do not understand your prescription, ask rather than guessing.
See our full prescription guide →
3. What is PD in glasses?
PD stands for pupillary distance.
It is a measurement used to help position the optical centres of your lenses correctly in relation to your eyes.
People often assume their PD must appear on their spectacle prescription, but it frequently does not.
That does not necessarily prevent you from ordering glasses online.
What you should not do is simply guess it.
An inaccurate measurement can position the lenses incorrectly, which becomes increasingly important with stronger prescriptions and more complex lens designs.
Read: How to buy glasses online if you don't know your PD →
4. What glasses suit my face shape?
This is one of the most common eyewear questions — and face shape is only part of the answer.
You will often hear rules such as:
- Round faces should wear square glasses.
- Square faces should wear round glasses.
- Oval faces can wear anything.
They can be useful starting points, but they are not laws.
Bridge fit, frame width, eyebrow position, colour, personality and your prescription can all matter just as much as whether somebody describes your face as round or square.
A frame that theoretically 'suits' your face but constantly slides down your nose is not the right frame.
Virtual Try-On can be extremely useful for comparing shapes and colours, but think of it as a digital mirror rather than a fitting appointment.
See how to use Virtual Try-On properly →
5. What are varifocal lenses?
Varifocal lenses — also known as progressive lenses — allow different viewing distances to be corrected within one lens.
Typically that means:
- Distance vision towards the top.
- Intermediate vision through the middle.
- Reading vision towards the bottom.
Unlike bifocals, there is no visible line separating the different powers.
However, not all varifocal lenses are identical.
Lens design, corridor width, usable intermediate area, frame choice, prescription and fitting measurements can all influence how comfortable a varifocal feels.
This is why simply asking, "How much are varifocals?" does not tell you very much about the lens you are actually buying.
Read our complete guide to varifocal lenses →
6. How long does it take to get used to varifocals?
There is no single answer.
Some people put on a well-fitted pair of varifocals and adapt remarkably quickly. Others need a period of adjustment while they learn to move their eyes and head naturally through the different areas of the lens.
First-time wearers will usually notice the change more than somebody who has worn varifocals for years.
But adaptation should not be used as an excuse for glasses that have been poorly measured or fitted.
If vision continues to feel wrong, the prescription, measurements, frame fit and lens design should be reviewed rather than simply being told to "keep trying."
At Burghley & Co, the chosen frame is sent out before varifocal lenses are manufactured so the measurements can be reviewed around how that particular frame actually sits.
See how Burghley & Co fits varifocals online →
7. Do blue light glasses actually work?
This is one area where eyewear marketing can get ahead of the evidence.
Blue light filtering lenses can reduce a proportion of blue-violet light passing through the lens, but they should not be presented as a miracle cure for computer-related eye strain.
Current evidence does not strongly support claims that blue-blocking spectacle lenses generally prevent eye strain, improve sleep or protect eye health in the general population.
If your eyes become uncomfortable while using a computer, there may be other factors involved, including:
- An uncorrected prescription.
- Dry eyes or reduced blinking.
- Poor screen position.
- Incorrect working distance.
- Long periods without breaks.
- Using lenses designed for the wrong viewing distance.
For some people, an appropriate computer or occupational prescription may make considerably more difference than simply adding a blue light filter.
Read our Blue Light Glasses: Facts vs Myths guide →
8. Are polarised lenses worth it?
For the right person, absolutely.
Ordinary tinted sunglasses primarily reduce the amount of light reaching your eyes.
Polarised lenses go further by helping reduce reflected glare from surfaces such as roads, water and other bright horizontal surfaces.
That is why they can be particularly useful for:
- Driving.
- Fishing.
- Holidays.
- Walking near water.
- Bright outdoor environments.
They are not essential for every sunglasses wearer, but once somebody who is particularly sensitive to reflected glare has experienced good polarised lenses, they often appreciate the difference.
Prescription polarised lenses are available too.
Learn more about polarised prescription lenses →
9. What are Transitions or photochromic lenses?
Photochromic lenses change their level of tint according to the light conditions around them.
They are designed to remain relatively clear indoors and darken when exposed to suitable ultraviolet light outdoors.
Transitions® is one well-known brand of photochromic lens technology, although the words are sometimes incorrectly used interchangeably.
They are a convenient option for somebody who regularly moves between indoor and outdoor environments and does not want to keep swapping between clear glasses and sunglasses.
There is one important point to understand: many photochromic lenses do not become as dark inside a car as they do outside because the windscreen filters much of the UV required to activate them.
If driving glare is your main concern, a dedicated pair of prescription sunglasses may still be preferable.
Read our Photochromic Lenses Explained guide →
10. What do 1.50, 1.60, 1.67 and 1.74 mean on lenses?
These numbers describe the refractive index of the lens material.
In straightforward terms, a higher-index material bends light more efficiently, allowing stronger prescriptions to be produced using less material.
That can result in thinner lenses.
Common lens indexes include:
- 1.50 — standard lens material, suitable for many lower prescriptions.
- 1.60 — a thinner option often suitable for moderate prescriptions.
- 1.67 — a super-thin option commonly considered for stronger prescriptions.
- 1.74 — one of the thinnest commonly available plastic spectacle lens materials for high prescriptions.
But higher does not automatically mean better.
If you have a relatively low prescription, paying for a 1.74 lens may provide very little meaningful benefit.
Compare 1.50, 1.60, 1.67 and 1.74 lenses →
11. Do I need thinner lenses?
Possibly — but your prescription is only half the story.
Lens thickness is also influenced by the frame you choose.
A very large frame can produce considerably thicker lens edges in a minus prescription than a smaller, well-centred frame made using the same lens material.
For this reason, somebody with a stronger prescription may sometimes achieve a better cosmetic result by choosing the right frame and a sensible high-index lens rather than simply buying the most expensive lens material available.
This is one of the reasons we encourage customers with stronger prescriptions to ask before ordering.
Good dispensing is about finding the right combination of prescription + frame + lens.
Not automatically choosing the most expensive option.
Find out which lens index may suit your prescription →
12. Is anti-reflection coating worth it?
For somebody who wears their glasses regularly, it is one of the lens features I am much more likely to recommend.
Anti-reflection — often shortened to AR — reduces reflections from the surfaces of the lenses.
This can:
- Make the lenses appear clearer.
- Reduce distracting reflections.
- Improve the cosmetic appearance of the glasses.
- Help with visual comfort in challenging lighting conditions.
You can often spot inexpensive uncoated lenses because strong reflections obscure the wearer's eyes.
Not all anti-reflection coatings are the same, however. Durability, scratch resistance, ease of cleaning and residual reflection can vary considerably between products.
Burghley & Co clear prescription lens options include premium anti-reflection coating as standard.
Read our guide to choosing prescription lenses →
13. Can I put new prescription lenses into my existing glasses?
Yes, in many cases.
If you have a frame you love, changing the lenses rather than replacing the entire pair can make perfect sense.
The frame needs to be assessed for condition and suitability before new lenses are fitted.
Older, damaged, brittle or specialist frames may require additional consideration because glazing places some stress on the frame.
For suitable frames, reglazing can be particularly attractive when:
- Your prescription has changed.
- Your lenses are badly scratched.
- You want thinner lenses.
- You want to turn an existing frame into prescription sunglasses.
- You simply cannot find another frame you like as much.
Replacing the lenses can give a favourite pair of glasses an entirely new life.
See how our replacement lens service works →
14. What are the best glasses for driving?
There is no single "driving lens" that is right for everybody.
The first priority is having the correct prescription.
After that, useful considerations may include:
- A good-quality anti-reflection coating for clear lenses.
- Polarised prescription sunglasses for bright daytime conditions.
- A frame that gives a comfortable field of view.
- A suitable varifocal design if you need distance and dashboard vision.
Be cautious about products marketed as universal night-driving glasses.
A strong coloured tint at night reduces the amount of light reaching the eye, which is not automatically desirable in already low-light conditions.
If night driving has suddenly become more difficult, particularly because of glare or halos, it is worth arranging an eye examination rather than assuming a particular spectacle coating will solve the problem.
Explore prescription polarised lenses for daytime driving →
15. Are expensive glasses actually better?
Sometimes. But price alone tells you very little.
An expensive designer frame does not automatically give you better vision than an inexpensive frame.
Likewise, paying more for a lens upgrade you do not need does not automatically improve your glasses.
What matters is where the money is being spent.
A higher price may reflect:
- Frame design and construction.
- Materials such as quality acetate or titanium.
- Brand licensing and design.
- A more sophisticated lens design.
- Thinner lens material.
- Higher-quality coatings.
- More individualised fitting and measurements.
The better question is not:
"Are expensive glasses worth it?"
It is:
"Am I paying for something that will actually improve the way these glasses look, fit or perform for me?"
That is where professional advice becomes valuable.
The question we wish more people asked
After all 15 questions, there is one we would add:
“Are these frames and lenses actually right for my prescription?”
It is easy to shop for glasses as though the frame and lenses are completely separate products.
They are not.
Frame size can affect lens thickness. Bridge fit can affect where the glasses sit. Lens design can influence which frame depths work well. Your prescription can make an oversized frame either perfectly sensible or a poor choice.
The best pair of glasses is not necessarily the most expensive frame or the thinnest lens.
It is the pair where the frame, prescription, measurements and lens design work together.
That is the principle behind Burghley & Co.
We combine designer eyewear with premium prescription lenses and professional review from a UK Registered Dispensing Optician, while keeping the convenience of ordering online.
If you know exactly what you need, you can order online.
If you don't, ask.
We would rather help you choose correctly before the lenses are made.