[Intraocular pressure assessment before and after photorefractive keratectomy using static, dynamic and noncontact pneumotonometry [air puff]]

ABSTRACT

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]. 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. 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]. 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