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

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.