Influence of corneal biomechanics on Ortho-K fitting

Purpose. The aim of this clinical observation was to investigate the influence of corneal biomechanics on the fitting of orthokeratology contact lenses.

Material and Methods. The measurements were performed in a single-center, longitudinal user observation with n = 17 subjects aged 18 to 43 years. Refraction and corneal topography were determined during the initial examination. Biomechanical parameters such as strain-stress index (SSI) and stiffness parameters (SP-A1) were recorded using Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany). After wearing the contact lenses for the first time, four two-day consecutive follow-up appointments followed to document the decrease in the spherical equivalent and the corneal radii. At the last appointment, the corneal biomechanics were recorded again.

Results. The initial results showed a mean distribution of the spherical equivalent of −2.38 ± 0.95 D and a mean distribution of the apical corneal radius of 7.64 ± 0.26 mm and 7.71 ± 0.26 mm of the flat corneal radius. The corneal biomechanical parameters were 1.12 ± 0.17 (SSI) and 101.86 ± 11.71 mmHg (SP-A1). Changes in the parameters (SEQ, apical and flat corneal radius) occurred in the adaptation process, especially in the very high and low stiffnesses between the third and seventh night. Corneal biomechanics also changed as a result of adaptation (p < 0.001). The mean SSI was 1.12 ± 0.17 at baseline and 1.05 ± 0.16 after the seventh night. The stiffness parameter was 101.86 ± 11.71 mmHg at baseline and 105.45 ± 11.34 mmHg after the seventh night.

Conclusion. Fundamental changes in the orthokeratologic
effect were recorded by corneal biomechanics. The adjustment of corneal biomechanics during Ortho-K treatment allows conclusions to be drawn about the orthokeratologic effect, but these are only possible after a certain period of time.