How to choose prescription glasses frames: prescription strength, lens type and fit

To choose the right prescription glasses frame, start with your prescription and lens type, then size and how the frame sits on your face, and leave face shape and colour for last. A strong prescription looks better and feels lighter in a smaller, full-rim frame centred on your eyes; progressive lenses need a frame deep enough for their distance, intermediate and reading zones; and no frame works unless your eyes sit near the middle of each lens and the bridge rests steadily on your nose. The American Academy of Ophthalmology adds a point on budget: spending more on frames does not mean better-quality glasses, but you should not skimp on lenses, especially progressive ones. This guide walks through each decision in the order an optician would.

Start with your prescription, not the look

The same frame can suit one prescription and fail another, because lens thickness follows the prescription. A lens for nearsightedness (a minus number on your prescription) is thinnest in the middle and thickest at the edge, so the bigger the lens, the thicker the edge that shows at the side of the frame. A lens for farsightedness (a plus number) is the opposite: thickest in the centre, so a bigger lens means a thicker centre and heavier glasses. Either way, a smaller lens area means less thickness and less weight. The lens material helps too. EyeWiki, the American Academy of Ophthalmology's medical encyclopedia, defines high-index materials as those with a refractive index of 1.60 or higher, says their main use is thin, better-looking lenses for strong prescriptions, and notes that polycarbonate lenses can be up to 30% thinner than regular glass or plastic lenses.

• Strong nearsightedness: choose a smaller lens in a full-rim frame; a thick plastic rim hides more of the lens edge than a thin metal one.
• Strong farsightedness: a smaller lens keeps the centre thinner and the glasses lighter on your nose.
• Rimless frames (lenses held by screws drilled through them): the American Academy of Ophthalmology says Trivex or polycarbonate lenses work with them, and with a strong prescription the whole lens edge is on show.
• Centring: your pupils should sit near the middle of each lens. If the frame is much wider than the distance between your eyes, the lab has to shift the lens centres and cut each lens from a larger blank, so it comes out thicker.

Each material has trade-offs. EyeWiki notes that polycarbonate produces colour fringing that is most noticeable in strong prescriptions; that Trivex is the lightest lens material available but needs thicker lenses at higher powers, while staying comparably thin around ±3.00 dioptres; and that none of the high-index materials pass the American National Standards Institute's impact-resistance standards. It adds that polycarbonate is often recommended for children, active people and safety eyewear. So for a child's glasses or for sport, impact resistance may matter more than thinness.

Your lens type decides which frames will work

Single-vision lenses, which correct one distance only, fit almost any frame. Progressive lenses are different. The American Academy of Ophthalmology explains that you look through the top of a progressive lens for distance, the middle for intermediate distances and the bottom for close-up, with the prescription changing gradually across the lens surface. All three zones have to fit inside the frame, so a very shallow frame can cut off part of the reading area. Each progressive design has a minimum fitting height set by its manufacturer, so ask the optician to check the frame you like against the lens you are buying before the order is placed.

The Academy also says progressive lenses can cause more distortion than other lens types and are difficult to wear for about 10% of people, that adapting can take anywhere from a week to a couple of months, and that the lenses should be customised and fitted by a licensed ophthalmologist or optometrist. Computer glasses, a type of progressive that gives more of the lens to intermediate distance, are designed for screens usually about 20 to 26 inches, or roughly 50 to 66 cm, from the face.

• Single vision: works with most shapes and sizes; the main limit here is the prescription, not the lens type.
• Progressive: needs enough depth below the pupil for the reading zone, so avoid frames that are very narrow from top to bottom.
• Bifocal: corrects reading at the bottom and distance at the top, with a visible dividing line, and also needs a frame deep enough for both parts.
• Computer or office lenses: more room for intermediate distance, with the same depth considerations as progressives.

Size and comfort: how to tell a frame fits you

The American Academy of Ophthalmology lists nine parts of a pair of glasses, and three of them decide most of the comfort: the bridge, the centre of the frame that rests on your nose and joins the two rims; the nose pads, which give a more comfortable and secure fit; and the temples, the arms that run over your ears. On metal frames, the small pad arms that hold the nose pads are adjustable to fit the shape of your face, which helps if your glasses keep sliding. The three numbers printed inside the arm (lens width, bridge width and arm length) are covered in the frame size guide; in the shop, these signs matter more than the numbers:

• Your eyes sit near the horizontal centre of each lens, not close to its inner or outer edge.
• The frame is about as wide as your face at the temples: it does not stick out beyond your face, and the arms do not press on the sides of your head.
• The lenses do not touch your eyelashes, and the bottom of the frame does not rest on your cheeks when you smile.
• The bridge sits evenly on your nose and leaves no red marks after a few minutes. If the bridge of your nose is low and glasses slide or sit on your cheeks, a frame with adjustable nose pads usually solves it.
• The arms curve down behind your ears and hold the glasses without squeezing your head; this matters more with a strong prescription, because thick lenses are heavier.
• Look down at the floor and move your head gently: the frame should stay in place.

Face shape and style: the contrast rule

Once a frame passes the prescription and fit tests, the look is your call. The common rule of thumb is contrast: a frame that balances your features rather than repeating them. These are guidelines, not rules, and the frame you are happy to wear every day is the right one:

• Round face: rectangular or square frames with corners add definition.
• Square face: round or oval frames soften strong angles.
• Oval face: most shapes suit it, as long as the frame is about as wide as the widest part of the face.
• Heart-shaped face (wide forehead, narrow chin): a frame with a lighter top line or a little more width at the bottom balances the upper face.
• With a strong prescription: pick the smaller version of the shape you like; the same shape with a smaller lens is thinner and lighter.

Frame material and budget: where to spend and where to save

According to the American Academy of Ophthalmology, plastic frames are the most popular choice because they are usually less expensive, light and available in many colours, but they break more easily than metal frames and their colour can fade slightly over time. Titanium frames are very strong, light, corrosion-resistant and hypoallergenic, which matters for people allergic to metals such as nickel. Blended nylon is strong and light and common in sports and safety frames, and soft plastic frames suit infants and small children. On budget, the Academy is direct: you do not need designer frames to have a good pair of glasses, but you should not skimp on lenses, especially bifocal, trifocal or progressive ones, because lenses with a wide reading area that minimise distortion are well worth the cost. Before you pay, go through these points with the optician:

• Bring your latest prescription and say how you use your glasses: driving, screens or reading.
• Ask which lens material and index suit your prescription, and how thick the edge will be in the frame you chose.
• With progressive lenses, confirm the frame is deep enough for the design you are buying.
• Make sure your pupillary distance is recorded, and ask for the frame to be adjusted to your face when you collect your glasses.