Background: The intracorneal ring has been advanced as a mechanical device for the correction of myopia. The device may reduce refractive error, but the effect on the overall optical performance of the eye has been neglected. This paper addresses this issue by presenting mathematical models that will predict the effect of the intracorneal ring on refractive error, corneal asphericity, and the spherical aberration of the eye.
Materials and methods: Algorithms are derived for predicting the corneal apical radius, asphericity, and the change in myopia after inserting intracorneal rings of any thickness and diameter.
Results: The model predicts that the magnitude of myopia reduction is a function of both ring thickness and diameter. The large diameter (9 to 10 mm), thin (0.1 to 0.2 mm) intracorneal ring is less likely to adversely affect corneal asphericity and therefore not significantly enhance the spherical aberration of the eye.
Conclusions: An intracorneal ring cannot correct more than 4.00 diopters (D) of myopia without significantly increasing ocular spherical aberration, which, in turn, will compromise the final visual outcome.