Analyzing corneal biomechanical response in orthokeratology with differing back optic zone diameter: A comparative finite element study.

Abstract

Purpose: To investigate the impact of orthokeratology (ortho-k) lenses with different back optic zone diameter (BOZD) on the biomechanical response of the cornea, focusing on contact pressure, displacement, and stress distribution.

Method: Finite element models were developed to simulate varying corneal curvatures (39.0D, 42.0D, 45.0D) and ortho-k lenses designed to target myopia reductions of -2.0D, -4.0D, and -6.0D, with BOZD values of 5.0 mm and 6.0 mm. Key parameters-contact pressure, displacement, mechanical treatment zone (MTZ) diameter and von Mises stress-were calculated and compared across the models.

Result: The BOZD = 5 mm group demonstrated higher central contact pressure and greater central corneal displacement compared to the BOZD = 6 mm group. Additionally, the BOZD = 5 mm group exhibited a smaller central contact range, corneal reshaping range, and MTZ diameter than the BOZD = 6 mm group. The maximum stress decreased and shifted locations from the center to the periphery after lens application in both groups, with a more significant decrease observed in the 6 mm group.

Conclusion: BOZD plays a crucial role in corneal biomechanical responses during ortho-k treatment. Smaller BOZD lenses result in a more concentrated contact area, leading to a smaller corneal reshaping area and MTZ diameter without significantly increasing the maximum stress in the cornea.