His doctor immediately made French an appointment with an eye specialist, who ran more accurate tonometry tests and found that his IOP was more than 30 millimeters of mercury (mm Hg). Normal IOP is between 10mm and 21 mm Hg.

IOP in French's eyes had built up because the aqueous humour - the clear liquid that fills the eye - was not draining properly from the channels in the front of his eyes in an area called the anterior chamber angle, or simply the angle. The excessive pressure was progressively damaging French's optic nerves and shrinking his field of vision from the edges in, creating 'tunnel vision'.

French had open angle glaucoma - an irreversible and incurable condition that is the leading cause of blindness in Hong Kong. French had already lost 90 per cent of the sight in his right eye, and sight in his left eye was beginning to deteriorate. The priority now was to control the IOP and prevent any further loss of sight.

He was given an injection to bring down the IOP and sent home with eye drops to help slow the production of the aqueous humour and to speed its drainage from the eye.

After six months on the eye drops, French's IOP was still too high, and more drastic measures were needed to control the condition. Doctors wanted French to consider a surgical procedure commonly used to treat glaucoma called trabeculectomy, in which the clogged trabecular meshwork - channels that normally help drain the aqueous humour - is removed and a new drainage valve is created.

The idea of cutting into a body part as sensitive as the eye made French very nervous. But his wife's friend had also recently completed a trabeculectomy and highly recommended her doctor, which made him feel slightly more assured. So he took the plunge.

During the procedure, which lasted less than an hour, French was under local anaesthesia and awake while the surgeon cut into his right eye. After the surgery, antibiotics were applied to the eye, which was taped shut and protected with an eye patch. French then had daily injections into his eye for almost a week to prevent the incision from closing.

Despite the successful trabeculectomy, French still has to have two types of eye drops daily for life. He also has to visit the eye specialist for regular tests, including a visual field test to monitor any further loss of his peripheral vision.

While the glaucoma was stopped in time for French not to have to suffer any major upheavals to his lifestyle, he still wishes that there was greater accessibility to the simple air-puff tonometry test that could help detect glaucoma early.

'If this simple test was included during regular eye checks in Hong Kong, [glaucoma] would be picked up much earlier, and many people could avoid the life-long process of dealing with glaucoma and its on-going medical costs,' says French, who pays more than HK$550 for his medication every month.

With early detection and good care, open angle glaucoma patients like French can prevent further loss of vision.

The condition often runs in families. French eventually discovered that an aunt also suffered from glaucoma. Experts advise that people over 40 years old should have an eye examinations once every five years. Those with high-risk factors such as family history; systemic diseases such as diabetes, hypertension or migraine; severe near-sightedness and steroid use should consider getting even more regular eye examinations.