[A study on the effect of the corneal biomechanical properties undergoing overnight orthokeratology].

OBJECTIVE: To evaluate the changes of corneal biomechanical properties and corneal topography undergoing overnight orthokeratology treatment. METHODS: Thirty teenagers with low and moderate myopia with age of 11.67 + or - 1.63, myopia (-2.56 + or - 0.86) D, were included and were fitted with Ortho-K CL. The corneal biomechanical properties, including corneal hysteresis (CH), corneal resistance factor (CRF), goldmann-correlated IOP (IOPg) and corneal-compensated intraocular pressure (IOPcc) were measured with ocular response analyzer (ORA). Corneal topography, central corneal thickness (CCT) and corneal endothelium density were measured with computerized corneal topography, optical coherence tomography (OCT) and non contact specular microscope respectively. The measurements were taken at pre-wear, 1 day and 7, 30, 90, 180 days after orthokeratology. Only data from the right eyes were analysed. RESULTS: All subjects were significantly reduced the myopia amount after 1 day of lens wear. The corneal curvature flattening (F = 38.837, P < 0.01) became slightly down to stable after the first week. There were significant decrease in CH and CRF after the orthokeratology treatment within the first week, and CH and CRF reversed and thereafter into the original level at 3-month and 6-month follow up. IOPg and IOPcc decreased and reached the lowest level at 1-week visit and after then became down to stable. There were significant reduction in CCT after 1 week (F = 4.739, P < 0.05). There were no significant changes in corneal endothelium density during orthokeratology treatment for 6 months. CONCLUSIONS: The amount of myopia reduction with orthokeratology occurred mostly within 1 week while the corneal biomechanical properties such as CH and CRF were decreased. However the corneal biomechanical properties are reversal to the original level thereafter and remain unchanged within the 6 months follow up visits. It proves that orthokeratology does not damage corneal microstructure. The early sign of reduction may due to the temporal response to the reshaping of the cornea.