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IOP significantly reduced in myopic and hyperopic eyes after LASIK
J Glaucoma. 2008;17(8):611-618.
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IOP was significantly reduced in myopic and hyperopic patients who underwent LASIK. The reduction was attributed to flap cutting and thinning of the central cornea, particularly in myopic eyes.
"This IOP reduction is stable even 1 year after LASIK, so it seems that healing cannot recover the normal stiffness of the cornea," the study authors said. "The observed reduction in IOP measurements after LASIK implies that IOP readings that would not be considered risky in nonoperated eyes may instead indicate high risk of suffering glaucoma in operated patients."
The study included 522 myopic eyes and 296 hyperopic eyes that underwent LASIK. Pneumotonometric IOP was measured before surgery, 1 month and 1 year after surgery.
In myopic eyes, the difference between mean IOP before surgery and 1 month after surgery was highly significant (P < .00001). The difference was also significant for hyperopic eyes (P < .00001). Myopic eyes showed a significant correlation between IOP reduction and central corneal thinning (P < .001). The correlation was not significant for hyperopic eyes (P > .10 with ultrasonic pachymetry and P > .03 with optical pachymetry).
On average, flap cutting reduced IOP 1.6 mm Hg ± 0.8 mm Hg. Ablation in the central cornea reduced IOP 0.029 mm Hg ± 0.003 mm Hg. For myopes, ablation occurs primarily in the central cornea. Ablation at the periphery of the optical zone does not affect post-LASIK tonometry, the authors said.
"This effect should be considered when evaluating the accuracy of IOP measurements in LASIK patients who are at risk for developing glaucoma," they said.