It's a Thursday evening in Topshop's Oxford Circus branch, and next to the frozen yoghurt stall a harem of teenagers is trying on glasses. Lured to the racks by the promise of a weekend heatwave, the girls switch from pair to pair - cat's eyes, jam jars, and computer nerd squares are all getting a look-in.
At first glance, there's nothing amiss - teenagers are as wedded to their sunglasses as they are to their iPhones, and ToyShades, the latest concession to take a space on Topshop's ground floor, sells glasses for a very reasonable £20 (NZD$42) per pair. But a second look is more surprising: the lenses are clear.
"By making the price accessible, we've made clear glasses a fashion accessory," says James Minor, the 34-year-old founder of ToyShades.
"You wouldn't walk into an optician and think, 'Today I'm going to try a pair of clear lens glasses even though I have perfect vision.' But in Topshop it's a no-brainer: you put them on, you look good, and they're £20."
The BYOP (bring-your-own-prescription) service costs £40 (NZD$84), and they can have frames ready in just one hour.
Minor isn't reinventing the wheel - glasses are medical devices that have been in use since at least the Egyptian times. In the third century BC, the philosopher Seneca reportedly read books using a glass globe filled with water to magnify the letters. But spectacles today are less an indication of poor eyesight, more an accessory to personal style.
When did glasses become cool?
Fashion, perhaps an unlikely supporter of the optically challenged, has helped: spectacles starred on the autumn/winter 2015 catwalks at Gucci and Max Mara, while Prada and Chanel's eyewear campaigns, starring Gemma Ward and Kristen Stewart respectively, have been well publicised.
Celebrities including Emma Watson, Cate Blanchett and Jennifer Aniston are spectacles-wearers; Meryl Streep, Karlie Kloss and Lupita Nyong'o have even thrown caution to the wind and frequently wear glasses to red carpet events (so popular are Nyong'o's square style that they have their own Twitter handle).
Meanwhile, Jenna Lyons, the creative director of J Crew, has become a postergirl for thick black frames from Moscot; and Bobbi Brown, whose make-up mogul image is bolstered by her black Superman frames, last year expanded her empire with a collection of frames with the Italian eyewear company Safilo.
"Having worn glasses for most of my adult life - Sissy Spacek round wire specs, New England preppy tortoiseshells - I realised that I didn't really like most glasses. They were either too fashion-y or weird for my liking," Brown said at the UK launch of department store Liberty last month.
"I wanted to make glasses that were stylish but not too over-the-top."
Eyewear, incidentally, is a lucrative business. The estimated worth of the global market, which includes frames, contact lenses and sunglasses, is US$90 billion, projected to reach $140 billion by 2020.
The premium fashion segment is occupied by a handful of firms: the Italian firm Luxottica, the world's largest eyewear company, owns Ray-Ban, Persol, and Oliver Peoples, as well as the licences to produce eyewear for fashion brands such as Chanel, Ralph Lauren, Armani and Prada. It also owns retailers including Sunglass Hut and LensCrafters.
"There's a sense of greed in eyewear," says Minor, "because the industry is so archaic. It's a kind of global price-fixing cartel and the cost is put on to the consumer."
The good news? Prescription glasses are now cheaper and more readily available than ever before. The revolution began in 2004 with budget online optical company Glasses Direct. Now brands such as Warby Parker in the United States, and Cubitts, Bailey Nelson and ToyShades in the UK, have taken up the cut-price optical mantle.
How to choose the right shape for your face
• The top of your glasses frame should follow the line of your eyebrows. Avoid having too much eyebrow above or below the frames. (But with sunglasses, make sure they cover your eyebrows, or you risk looking cartoonish.)
• Eyes should sit at the centre of each frame.
• Don't follow guidelines solely based on the shape of your face. You may have an oblong visage, but if you have a big nose, for instance, then that will be the feature you need to focus on.
• Choose a hue that is complementary to your eye colour to emphasise them.
Avoid round frames - angular shapes are better to lend your face definition. Cat's eyes can look great.
Most styles work well on a long, thin face, so focus on frames that enhance your features. Avoid thin frames that will elongate your face further.
Balance a pointed chin with frames that are thicker on the bottom, to add an appearance of width. Retro pin details will draw attention to the eyes.
Select frames with a low bridge or a wide keyhole to minimise the pinching effect.
Choose a dark frame with a strong, horizontal line. Avoid clear frames, these will elongate your forehead further.
Avoid a light-coloured frame with a dark nose piece - it will draw attention to the centre of the face. Instead, opt for larger frames, or ones with details on the arms.
Laura Imami, optician and founder of an eponymous eyewear brand tackles frequently asked questions
Why do my glasses leave marks on the sides of my nose?
When the nose pads are not properly adjusted or they are too tight, all the pressure goes on the nose, instead of being evenly distributed on the nose, head width and ears, and it leaves indents. This can be easily solved with appropriate adjustments by a professional.
Why do my glasses make me ache behind my ears?
If the arms of the frame are bent too tightly around the ears, you will end up with an unbearable ache behind the ears as well as deep indents around the nose. This is easily solved by loosening the arms and adjusting them properly.
When buying reading glasses off the rack in an emergency, how do I know which strength to go for?
A Off-the-shelf spectacles are only good for an emergency, as they will not have your exact prescription. It is always better to have them slightly weaker than usual. Get a book or a magazine and try to read with the lowest strength you can get away with.
What is the best way to clean my glasses?
The most basic, efficient option is Fairy Liquid. Run your glasses under water and put a tiny drop of dishwashing detergent on the tip of your finger to create lather on the lens. Then rinse with warm water and dry with a microfibre cloth. As most lenses nowadays have anti scratch and anti-reflection coating, they should be kept away from chemicals and high temperatures.
I have trouble finding glasses that don't slide off my nose. What can be done?
frame width, bridge size and fitting should be taken into consideration. Most of the time all you need is a professional adjustment and the frame won't slide off.
Why do titanium frames cost so much and are they worth the money?
Titanium is a light, strong and flexible non-corrosive material suitable for those with metal allergies. Despite their cost, titanium frames are worth the money if you are looking for a metal option, as they are more durable than "ordinary" frames.
Are you ever too old to consider having laser treatment for short-sightedness?
Technically, old age is not an issue. From a practical point of view, there is a need to consider presbyopia, ie, a person may need to wear reading glasses or may need monovision surgery. There is also a chance of cataract or other medical conditions, but if your eyes are healthy then there is no upper age limit.