Home › Learn › How to Choose Glasses That Actually Fit

GUIDE

How to Choose Glasses That Actually Fit

Written by Alvin · Manh Long Optical, 147A Le Duan, Cua Nam, Hanoi · Updated 11 September 2026

• Lens index by prescription: under 3 diopters use 1.60, 3–5 use 1.67, over 5 use 1.74.
• Five common face shapes, each suited to a different frame style.
• An eye test should always come before choosing a frame, not the other way round.

Why the right pair matters more than people think

Myopia rates in Vietnam are climbing fast. The World Health Organization estimates that 80-90% of children in Asia, Vietnam included, could be nearsighted by 2050. In urban areas the current rate already sits at 20-40%, with some schools in Hanoi and Ho Chi Minh City recording refractive error in up to 50% of students (source: suckhoedoisong.vn, citing WHO data, 2024). In practical terms, roughly two to five people you pass on the street are likely already wearing glasses or need to.

With more people wearing glasses, a badly chosen pair isn't just a cosmetic issue. A frame that doesn't suit the face makes people avoid mirrors and shove the glasses in a drawer. The wrong index makes a lens thick and heavy on the nose, uncomfortable after just a few hours. Both problems are solvable at the point of choosing, not after you've already taken the pair home.

Step 1: Work out your face shape before picking a frame

The old rule still holds: a frame should offset your face's lines, not repeat them. A round face suits an angular frame that adds visual length. A square face suits a rounded frame that softens the angles. The first job is figuring out which shape you actually are.

Five common face shapes

Stand in front of a mirror, pull your hair back, look straight ahead, and compare the width of your forehead, cheekbones and jaw:

• Round: width and length are close to equal, jawline is soft with no sharp angle.
• Square: forehead, cheekbones and jaw are close in width, jawline has a clear angle.
• Oval: forehead slightly wider than the jaw, proportions balanced, chin somewhat tapered.
• Heart: widest at the forehead, narrowing down to a pointed chin.
• Long (rectangular): length is noticeably greater than width, forehead, cheekbones and jaw close in width.

Not everyone fits neatly into one category — plenty of people are a blend of two, and in that case the jawline is the strongest deciding factor.

Quick-reference table: face shape to frame style

This table is a starting point, not a hard rule. At Manh Long Optical, customers try on several different frame shapes in person before deciding, because photos online and how a frame actually feels often differ, especially for a face that's a blend of two shapes. For a deeper look at frames for round faces specifically, see our face-shape frame guide, which also covers the styles currently in stock.

Step 2: Understand your prescription before choosing a lens

Once the frame style is settled, the step most people skip is lens index. This is what determines whether the lens ends up thick or thin, heavy or light — and directly affects whether the slim frame you just picked will actually be comfortable to wear.

What index means, and why a stronger prescription needs a higher one

Index measures how efficiently a lens material bends light. The higher the index, the thinner the lens at the same prescription, because the material bends light more efficiently and needs less of it. A lower index is cheaper, but at a strong prescription it produces a lens that's thick, heavy, and visibly bulges at the edge when viewed from the side.

Index by prescription

If your prescription is low and you choose the highest index anyway, you're paying extra for a difference you can barely see — the gap in thinness between 1.60 and 1.74 at 1-2 diopters is tiny. On the other hand, if your prescription is strong and you go with a low index to save money, the lens ends up thick and heavy enough to be uncomfortable wearing it all day. At Manh Long Optical, the eye test always comes before frame selection, because knowing the exact prescription is what makes it possible to recommend the right index and avoid a frame that doesn't suit the lens thickness.

Step 3: Choose a frame material that suits your lifestyle

Alongside lens index, frame material determines durability and how the glasses feel day to day. Four common materials, each suited to a different kind of wearer:

• Titanium: the lightest of the common materials, durable, doesn't rust, suits people who wear glasses all day or have sensitive skin prone to metal allergies. Usually priced a bit higher than other materials.
• Acetate (plastic): thicker, comes in more colors and patterns, gives more visual presence to the face. Suits people who like a frame with character and don't mind slightly more weight than titanium.
• Flexible plastic: bends without breaking under light impact, commonly used for children's frames or people who are physically active.
• Metal: slim, light, gives an understated look, usually more accessible in price than titanium.

At Manh Long Optical, all four materials are represented across roughly 1,000 frame styles in stock, priced 550,000-3,500,000d depending on material and design. Staff usually ask how many hours a day you wear glasses and whether you have a history of metal allergy before recommending a specific material.

Step 4: Consider functional lens features if you need them

Once the frame and base index are settled, some people need an extra coating or feature depending on their work and lifestyle:

• Blue-light filtering: suits people who use a computer or phone for many hours a day, and helps reduce eye strain from continuous screen viewing — not a treatment for an eye condition. (See also: Blue-light filtering and UV protection: what's the difference)
• Photochromic (color-changing) lenses: darken automatically outdoors and clear back up indoors — convenient for people who move between indoor and outdoor settings often. (See also: Photochromic vs polarized lenses: which should you choose?)
• Progressive lenses: for people who need both distance and near vision (typically after age 40), one lens handles multiple distances without switching glasses.

These features are optional add-ons, not requirements — choosing according to actual need saves more money than buying on the assumption that more features is always better.

Common mistakes when choosing glasses

The most repeated mistakes happen when customers choose glasses on their own without an eye test or an in-person try-on first:

• Choosing a frame from a photo online without trying it on. A flat photo doesn't reflect how a frame actually sits on real facial structure, especially nose bridge height and the distance between temples.
• Skipping the eye test because "my prescription is probably the same." Prescriptions can shift within 12 months, even in adults. Wearing the wrong power for an extended period tends to cause eye strain and headaches.
• Choosing the lowest index to save money despite a strong prescription. It saves a small amount upfront, but means living with a thick, heavy pair of glasses every day for at least the next year.
• Buying a rimless frame at a high prescription without asking first. Rimless frames need a sufficiently thin lens so the edge doesn't show — a strong prescription with an index that isn't high enough will leave a visibly thick edge, undermining the whole point of that frame style.

What the process should actually look like

The right order, the reverse of the common habit of picking a frame first: get the eye test first, choose the index based on the prescription, then try on frames based on face shape and preferred material. At Manh Long Optical, a single visit typically covers three steps: a free in-depth eye test (auto-refraction, a trial-frame check, binocular vision and astigmatism check, about 20-30 minutes), advice on frame style matched to your face and the index matched to your prescription, then cutting and fitting — single-vision lenses ready the same day, lenses that need to be ordered from the manufacturer get a pickup date.

The eye test is free even if you're not sure you'll buy glasses, and repeat tests are free with no limit afterward — so there's no need to feel awkward about "getting tested and not buying."

Common questions

How often should I get an eye test before choosing new glasses?

Adults should retest every 12 months, and children or people whose prescription is changing quickly every 6 months. Signs you need to test sooner: blurred vision with your current glasses, frequent eye strain, or squinting a lot at distance.

Can I work out my own face shape at home and buy glasses online without trying them on?

Recognizing your own face shape at home is a good starting point, but you should still try frames on before a final decision, since nose bridge height and the distance between your temples affect how a frame actually sits — both are hard to judge accurately from a photo.

Is a higher index always better?

Not necessarily. A higher index makes a lens thinner at the same prescription, but at a low prescription the difference in thinness between index levels is barely noticeable, while the price difference is significant. Index should be chosen to match your actual prescription, not on a 'higher is always better' assumption.

Do rimless frames suit every prescription?

Suits low-to-moderate prescriptions using a high-index lens. A very strong prescription with an index that isn't high enough will leave the lens edge visibly thick on a rimless frame — ask a staff member first if your prescription is over 5 diopters and you're considering this style.

Should the eye test and frame selection happen in the same visit or two separate visits?

Doing both in one visit works fine, and is usually more convenient — knowing your prescription first makes frame selection more accurate, and avoids ending up with a rimless or thin frame that doesn't suit your prescription.