Buying Spectacles: Lens Types, Coatings and Fit Explained
When buying spectacles, the frame is the part you see and the lens is the part that matters. A good pair comes down to five choices: lens material, coatings, the measurements taken on your face, how the frame fits, and what you decline to pay for.
Before you walk into the shop
- Bring: your latest prescription, your old glasses and a list of where you spend your day (screen, road, classroom).
- Worth asking about: anti glare coating if you drive at night or work on screens, a scratch coating, and thinner lenses only if your number is high.
- Always check: pupil distance and fitting height are measured on you, not guessed.
- Before you leave: put the finished pair on and test it in the shop.
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What kind of lens do I actually need?
Most people buying their first or second pair need single vision lenses: one prescription across the whole lens, for distance or for reading. If you are past your early forties and need help with both far and near, the choices are bifocals, progressive lenses or two separate pairs. That is a bigger decision, covered in our progressive and bifocal lens guide.
The numbers on your prescription decide the lens; how to read them is in the guide to SPH, CYL and axis. If you only need a simple pair for reading and your eyes are otherwise healthy, see whether readymade reading glasses or a tested pair suits you better. The NIH’s National Eye Institute describes glasses as the simplest and safest way to correct refractive errors, so a proper pair is not a luxury, it is the basic tool.
What does “high index” mean, and do I need thin lenses?
Index is how strongly the lens material bends light. A higher index bends light more with less material, so the lens can be thinner and lighter for the same number. Plastic lenses with a standard index are fine for small prescriptions. High index only earns its price when the number is strong, because a strong minus lens is thick at the edge and a strong plus lens is thick in the middle.
A simple rule: if your numbers are small, say so and ask for the standard lens. If the number is large and the frame is big, thinner lenses make the glasses lighter on the nose and look less heavy. Ask the optician to show you a sample edge so you can see the difference rather than take it on trust.
Which coatings are worth paying for?
| Coating | What it does | Worth it? |
|---|---|---|
| Scratch resistant | Hardens the surface of plastic lenses | Usually yes, especially for children |
| Anti glare | Cuts reflections, so less glare from headlights and screens | Yes if you drive at night or sit at screens |
| Photochromic | Darkens in sunlight, clears indoors | Handy if you hate switching to sunglasses |
| Blue light filter | Marketed for screens | See our honest verdict before paying extra |
Anti glare lenses show fingerprints and smudges more easily, so you will clean them more often. Photochromic lenses react to UV light, so they stay lighter behind a car windscreen. That is normal, not a fault.
Why does pupil distance matter, and why do wrong measurements cause headaches?
Pupil distance (PD) is the gap between the centres of your pupils in millimetres. The optical centre of each lens, the sweet spot, should sit in front of each pupil. If the lenses are made for a PD that is off, you look through the edge of the lens instead of the centre, and that can bring eye strain, a pulling feeling or headaches, especially with stronger prescriptions.
The same goes for height. The optician should mark where your pupils sit in the actual frame while you are wearing it. Online or readymade pairs that use a guessed PD can feel fine for someone with a small number and awful for someone with a larger one.
Insider tip: check the sweet spot before you pay
Put the finished pair on, look straight ahead at a distant object, and ask the optician to check that the optical centre sits in front of each pupil. Also ask them to write your PD on the receipt so any other shop can reuse it. Some shops refuse, which is worth knowing; if yours does, just ask for the number to be read out and note it on your phone yourself.
How should a frame fit?
- The frame should sit evenly on your nose without pinching or leaving deep marks.
- The arms should rest on your ears without squeezing the sides of your head.
- Your eyes should sit roughly in the middle of each lens opening, not at the top or the edge.
- Shake your head gently and look down. The glasses should not slide.
- Ask for the nose pads and arms to be adjusted if anything is off. This is free and normal.
Branded and local frames both can be good. Weight, flexibility of the arms and the quality of the hinges matter more than the logo. Flex the arms gently in the shop and check the hinge feels firm.
How should I handle upsells?
Shops make money on add ons, and some of them are useful. Be polite and specific: say what you do all day, then ask which of the extras would change that day. Ask for the price of each item separately. Skip anything the optician cannot explain in plain words.
Mild headache or a “swimmy” feeling in the first few days can happen as your eyes adjust, but it should settle. If headaches, double vision or distorted lines persist after about a week or two, go back to the shop for a recheck; the PD, height or number may be off. See an eye doctor promptly for sudden vision loss, flashes of light, a curtain over your vision, or a painful red eye, and do not rely on new glasses to fix those. This article is not a diagnosis.
New glasses do not replace a proper test. See the eye test schedule by age for how often to check, and this week test for screen headaches if you are unsure whether glasses are the cause. More guides live in Eye Care.
Questions people ask before buying glasses
How do I choose lenses for glasses?
Start with your prescription and your daily life. Most people do well with standard single vision lenses with a scratch coating, and add anti glare if they drive at night or use screens a lot. Add thinner lenses only for a strong number.
Is anti glare coating worth it?
Often, yes, if you drive at night or work on screens. It reduces reflections and halos from lights. It also shows smudges more, so you will wipe the lenses more.
What does high index lenses mean?
It means the lens material bends light more strongly, so the lens can be thinner and lighter for the same number. It matters mostly for strong prescriptions.
Are photochromic lenses worth it?
They suit people who move between indoors and outdoors often and do not want a second pair. They darken with UV light, so they stay lighter in a car, and they change speed with temperature.
What is pupillary distance?
It is the distance between the centres of your pupils, measured in millimetres. It tells the lab where to place the centre of each lens so it lines up with your eyes.
Why do I get a headache with new glasses?
A short adjustment period is common, but a headache that carries on can mean the PD, the lens height or the number is off. Return to the shop for a check after a week or two if it does not settle.
How long does it take to get used to new glasses?
Many people adjust within a few days to two weeks. Wear them as much as possible, because switching back to old glasses slows the process. If you still feel off after that, go back.
Are branded frames better than local ones?
Not automatically. Fit, weight and the quality of hinges and nose pads matter more than the label. Handle the frame, flex the arms, and wear it for a few minutes before you decide.
Can I ask for my pupil distance to be written down?
You can ask. A good shop will note it on the receipt. If a shop refuses, measure again elsewhere, or ask them to say the number aloud and write it down yourself.