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LE Pillunat, K Pollack, M Kohlhaas, E Spoerl; A Correction Formula for the Real IOP after Lasik . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1072.
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Purpose: The measured IOP values after Lasik are lower than real ones. The influence of the flap, of the changed corneal thickness and corneal curvature on the IOP-measurement with Goldmann applanation tonometry after Lasik is still unknown. Aim of this study was to evaluate a correction formula in order to determine the real IOP after Lasik assuming that the pre- and postoperative IOP-values are equal. Methods: 102 Lasik-treatments were performed. The pre- and postoperative IOP (applanation tonometry), keratometer values (topography), central corneal thickness CCT (ultrasound pachymetry) and ablation depth (Schwind Excimer Laser) were measured. Results: After Lasik (-6.3 2.17 D; -3D to -10 D) the mean CCT changed (P<0.001) from 541 µm to 465 µm and the keratometer values from 43.87 D to 38.4 D (P<0.001). The IOP changed (P<0.001) from 16 2.4 mmHg to 12.9 2.0 mmHg six months after the procedure. Multiple linear regression analyses showed a significant dependence of the measured IOP on CCT and keratometer values (r=0.59; P<0.001). A difference of 71 µm in the CCT corresponds to a difference of 1 mmHg in IOP and 2.7 D in the keratometer value causes 1 mmHg reduction in IOP. Correction formula: real IOP = measured IOP + (520 - CCT)/71 + (43-keratometer value)/2.7. Conclusion: After Lasik the measured IOP must be corrected by CCT and keratometer values according to the above formula. The biomechanical stability of the attached flap can be neglected.
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