Shoppers of middle to advanced age may remember well their first experience of struggling to read food and medicine labels due to weakened eyesight. They can now rest easier with an added set of eyes right in their wallets.

Dongguan Guanlong Photoelectric, a Chinese firm specializing in portable heaters, range-finders, and optoelectronic products for OEM manufacture, has developed a palm-sized magnifying lens that fits into a billfold credit card slot, making it ideal for taking on the road.

The company's latest 80-0027 model features a 48mm x 45mm acrylic lens of 2.5x magnification encased in a sleek stainless iron frame. The metal portion also contains space for a tiny white LED which runs on two standard CR2016 button cell batteries. The entire unit measures a scant 2.2mm in thickness.

The device is powerful enough to help the average nearsighted user make out miniature letters on books, cell phone displays, dials and labels in a pinch without having to don glasses. It also works in the dark, of course.

Dongguan sales executive Sara Sun displayed the company's newest product line at the April spring edition of the Hong Kong Electronics Fair, a collection that included an array of other light and compact reading aids. The company sports strong market shares in the U.S., Europe and Japan.

"Eye weakness is a problem that affects everyone as they age, so the demand is definitely constant from region to region," she says. "From that point, the ability to function is more a matter of what kinds of 'fixes' are available."

Presbyopia (the loss of the ability to clearly see close objects) is a normal byproduct of the aging process that begins around 40 in most people. It is often corrected with reading glasses and contact lenses. In poorer developing nations, however, glasses are far more difficult for the average person to obtain.

In 2000, VOSH (Volunteer Optometric Services to Humanity) reported that in three missions to southern Nicaragua in which eye exams were performed on nearly 5,800 individuals, over 50% were diagnosed as presbyopic.

A 2011 study by the Vision Impact Institute estimated 1.272 billion cases of presbyopia worldwide, corresponding to a productivity loss of $11 billion, or 0.016% of gross global economic output that year. It also found that the rates of presbyopia treatment varied widely - from 96% in Europe to as low as 6% in Africa.

"Even with conservative assumptions regarding the productive population, presbyopia is a significant burden on productivity, and correction would have a significant impact on productivity in lower-income countries," the study's authors concluded.

But the problem may no longer be confined to the aged. In Japan, one of the world's fastest aging countries, eye clinics around Tokyo have recently reported an increase of young people suffering from presbyopic symptoms, according to The Japan Times, quoting eyeglass industry survey results.

Data showed that the number of young people reporting presbyopic nearsightedness increased from 0.5% of their total number in 2012 to 6.7% in 2013. In nearby South Korea, diagnosed cases of presbyopia have more than doubled among people in their 30s over the past five years, the paper said. In both countries, the proliferation of smartphones, tablets, laptop computers, electronic books and car navigation systems are widely blamed for the problem.

"Of course, we don't discriminate among customers," says Ms. Sun. "At a wholesale price of under $4.00 per unit, we think that our product is cheap and convenient enough for anybody who needs help reading in a pinch."