a curable condition affecting the lens that focuses images onto the eye's retina.

A cataract occurs when proteins in the lens lose their normal arrangement,

clumping together in a way that causes discoloration or clouding,

and eventually blocks most vision.

Cataracts can be caused by eye injury,

certain medications,

ultraviolet radiation,

diabetes,

smoking,

or some genetic disorders.

But the most common cause is aging.

In the United States, more than 50% of people over the age of 80 develop them.

Cataracts were treated over 2,500 years ago in India,

though similar procedures may have existed even earlier

in Ancient Egypt and Babylon.

The most common procedure, called couching,

involved pressing a sharp instrument into the eye

to loosen and push the clouded lens out of the way.

Although this could increase the amount of light entering the eye,

the lack of a lens would leave the patient's vision out of focus.

Despite its low success rate, and high risk of infection or injury,

couching is still performed in some parts of the world.

Later procedures would also focus on removing the cloudy lens,

for example, by making an opening in the cornea to pull out the lens

along with the membrane capsule surrounding it.

While the invention of eyeglasses allowed for some restoration of focus,

they had to be extremely thick to help.

Furthermore, such techniques still caused complications,

like damaging the retina,

or leaving the eye with uncomfortable stitches.

But in the 20th century, something unexpected happened.

Eye surgeon Sir Harold Ridley was treating World War II casualties

when he noticed that acrylic plastic from a shattered aircraft cockpit

had become lodged in a pilot's eyes without triggering an adverse reaction.

This led him to propose surgically implanting artificial lenses into the eye

to replace cataracts.

And despite initial resistance,

the method became standard practice by the 1980s.

Since Ridley's discovery,

the intraocular lens has undergone several improvements.

Modern lenses can fit into the membrane capsule

that the cataract is extracted from,

leaving more of the eye's natural anatomy intact.

And the ability to fine-tune the lens curvature

allows the surgery to restore a patient's normal vision

without the need for glasses.

Of course, surgical techniques have also progressed.

Microscopic procedures use small instruments or lasers

to make precise incisions of one or two millimeters in the cornea,

while an ultrasound probe breaks up and removes the cataracted lens

with minimal trauma to the eye.

Low-tech versions of this operation have made the surgery quick and inexpensive,

helping it spread across the developing world.

Places like Aravind Eye Hospital in India

have pioneered high-volume, low-cost cataract surgery

for as little as six dollars.

Why then, with all these advances,

are there still so many blind people in the world?

The main issue is access to health care,

with poor infrastructure and a shortage of doctors

being a major barrier in many regions.

But this is not the only problem.

In many rural areas with poor education,

blindness is often accepted as an inevitable part of aging,

for which someone might not think to seek treatment.

This is why information is crucial.

Increased community awareness programs and the spread of mobile phones

mean that many of those

who might have remained blind for the rest of their lives due to cataracts

are now reachable.

And for them, a brighter future is in sight.