Home ::  Highbury Optometrists news ::  Why does my short sight keep getting worse?

Myopia or short sightedness is a very common condition affecting your ability to see objects at a distance.

Most people assume that they inherit their short sight from their parents, but this is not always the case. We know that identical twins quite often have very different prescriptions so genetics is not solely to blame.

Rates of short sightedness

Rates of short sight around the world are rising to epidemic proportions. Worst affected countries are Singapore, Hong Kong and Taiwan where around 80% of young adults are short sighted. This compares to around 20% a few decades back. In western countries rates are between 30-50% but are steadily rising.

Past theories and treatments

Many different theories as to what makes short sightedness worse have been proposed. Things such as reading too close or in the dark, too much TV or too much time spent on a computer have been blamed, but none of these theories have ever had strong scientific basis.

New research

A study by Ohio State University two years ago analysed the lifestyle of 514 children. They found that those that become more short sighted spent less time engaging in physical activity outdoors.

A theory was proposed that short sightedness was related to the amount of physical exercise. However an Australian study found no link between physical exercise either indoors or outdoors and rates of short sightedness. What they did find however was that rates of short sight was very well correlated to the amount of time spent outside.

Exposure to daylight maybe the key?

Further studies compared two groups of children, one in Singapore and one in Australia. On average the children in Sydney spent nearly 14 hours per week outside, and only 3 per cent developed myopia. In contrast, the children in Singapore spent just 3 hours outside, and 30 per cent developed myopia. Once again, close work had a minimal influence; the Australian children actually spent more time reading and in front of their computers than the Singaporeans (Archives of Ophthalmolology, vol 126, p 527).

It seems that the amount of exposure to outdoor daylight, which is many times more intense that indoor light, maybe a key factor in the progression of short sight.

The importance of peripheral blur

There are other factors that seem to influence short sight development, one of those is how light focuses in the peripheral retinal. Corneal refractive therapy (CRT)(also know as orthoK), was originally designed as a temporary solution to short sight, in which patients wear hard contact lenses overnight that temporarily reshape the cornea. In the morning, they take out the lenses and can see well for the rest of the day. CRT flattens the shape of the front of the eye (cornea) which reduces blur in the peripheral retina. Many studies have now shown that CRT lenses seem to reduce myopia development by 50% or more. (British Journal of Ophthalmology, vol 93, p 1181).

Spend time outside

So far it seems the one way to reduce the development of short sight might be to spend more time outdoors, avoiding sunburn of course! CRT lenses are certainly a great idea once short sight starts to develop.