Definition and Purpose

The reduced astigmatism of inserting a homogenous corneal ring indicates that astigmatism is rather due to inhomogenous tension of the cornea, than to partial inhomogenous thickness of the cornea. The corneal ring can not change inhomogenous thickness by homogenous circular tension but it can homogenise tensions. The tension theory therefore could explain the regular results in treating astigmatism and hyperopia with thickness law applications. Correcting refraction caused by tensions by applying the thickness law might be possible to some extent. However, superposition of the two effects seems limited. Putting the theory of tension release in practice would suggest that "intelligent" partial destruction of the Bowman's layer could change most refractional malfunction without getting deeper than 80ĩm. However, techniques depending on the change of cornea's biostatics will always lower the overall stability of the eye. Working with tension release, only the future will reveal, if the loss in stability will have secondary effects, as the hyperopic shift did after radial keratotomy.

In the authorīs point of view, procedures working with the simple "mechanic" thickness law are most predictable in their outcome, as they do not depend on the cornea's biostatics changes and have the advantage of 30 years' experience and therefore no long term surprises are expected. Moreover, they hold a successful experience of over thirty years, and unexpected long term effects have not occurred in that time. However, it must be secured that the effects of the thickness law are not biased by statical changes. That is to say, that the Bowman's layer must be saved and at least 400ĩm of tissue must be left in the cornea's center.  The superficial PRK function, although designed by the thickness law, does not meet this condition, as it destroys the Bowman's layer most likely changing eyes overall static’s. Tension release might have its place in correcting astigmatism caused by inhomogenious corneal tension. Figure 1 gives an overview of surgical correcting refraction.