In his 20s, Jay (not his real name) lived with a chronic neck ache for a few years.

When he finally decided to seek medical help, the results were not at all what he expected, given his relative youth. He was diagnosed with two medical conditions - obstructive sleep apnoea (OSA) and early glaucoma. He was only about 30 years old and the prospect of losing his sight was distressing.

OSA occurs when the throat intermittently relaxes and blocks the airway, causing breathing to repeatedly stop and start during sleep.

Glaucoma is a serious eye condition that damages the optic nerve, resulting in vision loss and blindness.

A recent study here showed that those with moderate to severe OSA are more likely to have glaucoma.

Jay was one of the 100 people who took part in a prospective study by Singapore General Hospital (SGH) and the Singapore National Eye Centre (SNEC) examining the prevalence of the eye condition in those with OSA.

The study, conducted between 2013 and 2014, showed that 8 per cent of patients here with moderate to severe OSA also had open angle glaucoma with normal pressure.

In comparison, the prevalence of glaucoma in the general population is 3.2 per cent for all forms of glaucoma and 1.4 per cent for open angle glaucoma.

The impetus for the study came from an increasing number of overseas studies linking OSA with glaucoma, said Dr Desmond Quek, a consultant at SNEC. "We wanted to see if the prevalence of glaucoma in OSA patients in Singapore was comparable to rates quoted in other publications, and if it was necessary to put in recommendations for screening of those with high risk."

Indeed, the findings came close to those of overseas studies published last year which showed that, overall, those with OSA were three times more likely to have glaucoma than those without OSA.

The Singapore study was presented during the 3rd Asean Sleep Congress last November at SGH.

Half of the local patients diagnosed with glaucoma have both structural and functional damage, and the other half have early glaucoma, with structural damage but no functional damage yet, said Dr Quek. Structural damage refers to the thinning of the nerve-fibre layer around the optic nerve head which precedes functional damage or loss of vision, he said.

Eyes with glaucoma also tended to be longer in length and are more myopic.

Crucial to detect glaucoma early

While the association between various eye conditions and OSA is clear, the reasons for this connection are not well understood.

One possibility is that OSA increases resistance to blood flow to the optic nerve, said Dr Quek. This creates a transient drop in oxygen supply, thus damaging the nerve.

Early detection and treatment can slow the progression of glaucoma, although vision already lost cannot be reversed, he said, hence the importance of screening, early detection and treatment.

The first-line treatment is using eye drops to lower the eye pressure and thus prevent further nerve damage. If eye drops fail to lower the pressure, more invasive forms of treatment like surgery may be required.

Based on published studies, OSA seems to have the strongest relationship in causing harm to eye health, among all the other sleep disorders, said Dr Toh Song Tar, director of the sleep disorders unit and consultant in the department of otolaryngology at SGH.

And given that OSA is one of the most prevalent sleep disorders here, affecting three in 10 of those aged 40 and above, such a relationship is worrying.

OSA is also associated with floppy eyelid syndrome, swelling of the optic disc and leakage of fluid under the retina, causing visual impairment, said Dr Toh. About 70 to 80 per cent of those who suffer a painless sudden loss of vision also have OSA, he added.

The cost-benefit ratio of any screening programme has to be carefully calculated before a widespread programme can be implemented. However, doctors encourage patients with confirmed moderate to severe OSA to have their eyes screened for glaucoma.

Jay, now 31, is keeping his glaucoma under control with eye drop medication. He was also advised to get a machine to help send pressurised air into his airway through the nose. This helps to prevent his airway from collapsing when he sleeps and improves sleep quality.

"I didn't know much about glaucoma, but I knew that, like cataracts, it was something to worry about only when you're much older," said Jay, an English teacher now living in Japan.

He had consulted a variety of specialists such as ear, nose and throat surgeons and neurologists, and even did some physiotherapy before ending up at the sleep disorder unit in SGH. "I did the sleep test and was diagnosed with OSA," said the bachelor.

He was then asked if he could participate in the study about glaucoma. He joined the research thinking it would be beneficial to do an eye test since he has myopia. He didn't think he would have glaucoma.

"I was rather distraught at first, thinking that I might go blind and I was only about 30 years old."

After some research and consultation with SNEC doctors, he felt better. "I realised that, though glaucoma is chronic and the damage to the optic nerves is permanent, it can be controlled with proper medication. What I can do is to prevent further damage," he said.

Eye-care professionals around the world dedicate the month of March to increasing glaucoma awareness through educational activities and the media.