intraocular pressure assessment before and after photorefractive keratectomy using static, dynamic and noncontact pneumotonometry (air puff)

purpose: to compare the preoperative and postoperative measurement of intraocular pressure (iop) using goldman applanation tonometry (gat), the air puff and pascal dynamic contour tonometers (pdct) in eyes undergoing myopic and myopic astigmatic photorefractive keratectomy (prk). methods: in a descriptional -analytic and prospective study, a complete examination was performed at the slit lamp, followed by pachymetry and pentacam imaging in patients scheduled for prk.iop was measured in myopic and myopic astigmatic eyes before and 2 months after prk by gat, pdct and the air puff tonometer in a randomized sequence at similar times. 1) before prk the difference among the 3 tonometers in iop measurement was compared 2) after prk the difference among the 3 tonometers was compared in the same manner 3) the difference between pre-operative and post-operative measurements for each instrument was measured 4) finally dissimilarity of changes from preoperative to postoperative among the 3 instruments was compared. results: the study included 402 eyes (201 patients, 162 females, 39 males) with mean age of 28.7±7.03 (18-48). mean tonometry before prk with gat, pdct and air puff was: (15.44±2.79), and (16.81±3.39), (16.31±3.36) respectively. mean iop after prk with gat, pdct and air puff was: (12.04±2.63), (13.57±2.91) and (11.01±3.29) respectively. the difference between 3 tonometer in iop measurement was statistically significant (p<0.001). in the same manner the difference between 3 tonometer was statistically significant post operatively (p<0.001). there was statistically significant difference between mean pre-operative and post operative measurement taken by the three instruments (p<0.001). there was no statistically significant difference between mean changes preoperative with postoperative measurement taken by pdct and gat (p= 0.778). briefly pdct and gat underestimate iop approximately equally. there was a significant difference between mean changes preoperative with postoperative measurement taken by air puff compared with gat, and air puff compared with pdct (p<0.001). conclusion: measurements of iop may be underestimated after prk, by gat, pdct and air puff. this underestimation probably relate to biomechanical changes of the cornea after surface ablation.