It was said that the ancient Chinese used to sleep with sandbags over their eyes to improve their vision and opticians have long known that a side effect of wearing rigid lenses is briefly having good vision after removing them. This led to the search for a way to prolong the effect by reshaping the cornea, a science known as orthokeratology or Ortho-k (ortho – straight; keratology – relating to the cornea).
Orthokeratology uses rigid gas-permeable contact lenses, normally worn only at night, to improve vision through the reshaping of the cornea.

This method can be used as an alternative to eyeglasses, refractive surgery, or for those who prefer not to wear contact lenses during the day. These can include workers in dusty or air conditioned environments or allergy and hay fever sufferers for whom wearing contact lenses during the day can be very uncomfortable.
It is only since the 1990s when computerised corneal topography, allowing an accurate mapping of the curvature of the cornea, became available that it has been possible to create lenses with repeatable results.

Additionally, the development of new base materials for rigid gas permeable lenses provided much higher levels of oxygen permeability and opened up the possibility of orthokeratology becoming an overnight procedure.

Finally, the introduction of computer-controlled precision lathes meant that lens designs could be manufactured to sub-micron levels of accuracy thereby offering the prospect of high volume production becoming commercially viable. (Courtesy of Wikipedia)

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First Published November 2009

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