Dynamic contour tonometry for post-LASIK intraocular pressure measurements

Background: Standard applanation tonometers are subject to systematic errors when applied to corneas with non-standard properties. Dynamic contour tonometry has been proposed as an alternative method for obtaining correct IOP data from such corneas. We have examined its applicability for patients who have undergone LASIK surgery. Patients and Methods: 20 healthy individuals scheduled for bilateral myopic LASIK were selected. Pre- and postoperative examination (3 months) included applanation tonometry (Goldmann), contour tonometry, pachymetry, keratometry, and refraction. LASIK was performed with an MEL-70 Excimer Laser and a Hansatome Microkeratome. A tobramycin/dexamethasone preparation (Tobradex(R) eye drops) was prescribed during one week after surgery. Results: Applanation tonometry and contour tonometry furnished comparable IOP results prior to surgery (GAT: 15.1 +/- 2.2 mm Hg [mean+/-SD] DCT: 17.0+/-2.2 mm Hg), with corneal thickness ranging from 473-601 mum (mean: 555 mum). 3 months postoperatively, mean corneal thickness was reduced by -85 mum. Contour tonometer readings were not significantly different from preoperative results (16.0 +/- 2.4 mm Hg); whereas the Goldmann tonometer furnished significantly lower values at 11.8 +/- 1.3 mm Hg. Conclusions: Preoperative IOP measurements with the two types of tonometer were in good agreement. Post-operative results with the contour tonometer agree well with preoperative figures. However, the Goldmann tonometer furnishes values 3.3 mm Hg lower on average. This result is indicative of a significant measurement error of this device on post-LASIK eyes, which persists even 3 months postoperatively. The Dynamic contour tonometer appears to be suitable, reliable, and easy to use for IOP measurements after LASIK surgery.