[Theory of the T-incision of the cornea]

T-incisions are used for surgical correction of moderate corneal astigmatism. No theoretical models to explain the curvature changes have yet been described in the literature. This paper describes a biomechanical model intended to facilitate understanding of the effect of corneal flattening. The incisions cause the stress inside the untouched layers of the cornea to increase. Subsequently the strain also increases and so the curvature radius of the meridian perpendicular to the incision also increases. The calculated changes in the refractive power of the cornea are in good agreement with clinical data. The influence of the depth of the incision is explained quantitatively. Secondary parameters, such as the length of the incision and the size of the optical zone, are discussed.