Safety evaluation after LASIK surgery based on the linear creep property: a finite element analysis

Area of Science:

• Ophthalmology
• Biomechanical Engineering
• Corneal Surgery

Background:

• Laser-assisted in situ keratomileusis (LASIK) is a common refractive surgery.
• Understanding the biomechanical effects of LASIK is crucial for patient safety.
• Percent tissue altered (PTA) is a key factor in LASIK outcomes.

Purpose of the Study:

• To determine the effect of percent tissue altered (PTA) on corneal safety after LASIK.
• To analyze safety based on linear creep characteristics and biomechanical changes.

Main Methods:

• Corneal linear creep characteristics were modeled using a five-parameter generalized Kelvin-Voigt relationship.
• Finite element analysis was used to simulate displacement and stress distribution on corneal surfaces.
• Eye models with varying PTA were analyzed under physiological intraocular pressure (IOP).

Main Results:

• PTA exceeding 39% led to excessive corneal vertex displacement, surpassing preoperative glaucoma levels at average IOP.
• Increased PTA resulted in significant thinning and stretching of the central cornea due to IOP.
• At PTA > 39%, anterior stromal stress increased by over 20% compared to normal eyes, inducing deformation and corneal ectasia.
• Postoperative vertex displacement correlated with decreased viscosity ratio.

Conclusions:

• A PTA of less than 39% represents a safe threshold for LASIK surgery.
• This study provides a numerical basis for evaluating postoperative corneal behavior and refractive surgery outcomes.