By Steve Roberts 

Overnight contact lenses  can significantly delay the progress of myopia - otherwise referred to as short-sightedness where distant objects appear blurred - in children from seven to 12 years old as well as for those having mixed myopia and astigmatism according to a new study published by Hong Kong Polytechnic University. The specially designed corrective lenses work through an optical science known as orthokeratology or ortho-k which uses the mild pressure of closed eyelids during sleep to gently flatten the surface of the eye.

Myopia occurs when the eyeball is too long and the longer it is, the higher the degree of myopia. Ortho-k reverses this elongation to correct the myopia and these special overnight contact lenses  can be used as an effective alternative to glasses, laser surgery or for those who prefer not to wear contact lenses during the day.

A research team from the university's School of Optometry conducted a series of studies over three years. Team member Pauline Cho Wong Hie-Hua said a study of 78 children, aged seven to 10 and having myopia of between -0.50 and -4.00 diopters showed that for the 37 children who received ortho-k treatment, myopic progression was 43 percent slower than for the 41 children who wore glasses. The treatment was most effective in those aged seven to eight, the team said.

Another clinical study completed last year with children aged eight to 11 and having myopia of more than -0.50 diopters showed that by wearing overnight contact lenses  this slowed down the elongation of the eyeball by 63 percent. Hong Kong Academy of Orthokeratology vice president Chan Ying-Yee said ortho-k lenses are recommended for those aged seven and above as they are old enough to follow instructions on how to wear them.