​It is not known how many Singaporeans suffer from both deafness and blindness, or deaf-blindness.

The Singapore Association for the Deaf and Miss Lisa Loh, who cannot hear and is slowly losing her sight as well, know of 15 to 20 such individuals.

But there could be more as many deaf-blind people and their families are not in contact with anyone, Miss Loh said.

Mr Koh Poh Kwang, principal of Lighthouse School, said some children are born deaf-blind when their mothers get infected, for example, with the rubella virus, during pregnancy. The Lighthouse School is a special education school for the visually impaired and has had deaf-blind students.

Others can become deaf-blind because of Usher syndrome, a genetic disease which results in hearing loss, and a progressive loss of sight through retinitis pigmentosa.

Dr Ranjana Mathur, senior consultant at the Singapore National Eye Centre, said that while the exact incidence of Usher syndrome in Singapore is not known, it is estimated to affect three to four children in every 100,000 births.

It is the most common cause of deaf-blindness.

The most famous deaf-blind person is the late Helen Keller, an American who lost her hearing and sight when she was a toddler after contracting what was suspected to be scarlet fever or meningitis. Miss Keller, who earned a university degree, wrote books about her life and advocated for and raised funds for the blind. She also co-founded the Helen Keller Foundation to prevent blindness. She died in 1968, aged 88.

Singaporean Theresa Chan Poh Lin (below) is known as the Helen Keller of the East. She lost her sight and hearing at 14 because of meningitis. She was sent to the Perkins School for the Blind in the United States, where Miss Keller was educated.

In the US, Ms Chan learnt how to read, write and speak English and live independently. When she returned to Singapore, she was a teaching aide at the Singapore School for the Blind for about 20 years.

Film-maker Eric Khoo, who made a film Be With Me, starring Ms Chan, takes her out for a meal about once a year.

Now in her 70s, she communicates with him through e-mail. Said Mr Khoo: “She is very independent and that is so amazing. She is in good spirits, loves to eat and drink and somehow never ages.”