Intraocular Pressure Calculation in Myopic Patients After Laser-Assisted In Situ Keratomileusis

Background: Corneal refractive surgery is widely used worldwide. Myopia is the most common reason for laser-assisted corneal refractive surgery (LASIK) and one of the risk factors for glaucoma. Intraocular pressure (IOP) measurement becomes variable postoperatively as the results are affected by the decrease in corneal thickness and biomechanics. This prospective clinical case study attempted to establish a simple correction formula for the calculation of IOP in post-LASIK myopic patients. Methods: This study included 300 eyes of 150 patients with myopia and myopic astigmatism as a refractive error who underwent LASIK. IOP was measured preoperatively and 6 months postoperatively. Preoperative and postoperative corneal thickness as well as ablation depth were measured. Statistical analysis was performed to detect the relationship between ablation depth and change in IOP. An attempt was made to construct a correction formula for the calculation of post-LASIK IOP. Results: The age of the patients ranged between 18 and 50 (mean +/- SD 34.78 +/- 8.8) years. The spherical equivalent of refractive error ranged between -1.5 and -10 diopters. The mean IOP decreased significantly from 15.72 +/- 2.37 mmHg preoperatively to 11.71 +/- 2.24 mmHg postoperatively, with a mean difference of 4 +/- 1.75 mmHg (p<0.001). A positive correlation was detected between corneal thickness and IOP difference among patients both preoperatively and postoperatively (p<0.001). A positive correlation was identified between ablation depth and IOP change (p<0.001). The correction formula for IOP was established: Real IOP=4+0.7(preoperative IOP)-0.3(ablation depth). Conclusion: IOP measurements change after corneal refractive surgery with LASIK. A corrected formula may be a good option for the proper calculation of post-LASIK IOP.