Intraocular Pressure After Myopic Lasik: Corneal Flap Tightening With The Lasik Tonometer Vs Air Pulse From The Ocular Response Analyzer.

To evaluate the agreement of corneal-compensated intraocular pressure (IOPcc, from Ocular Response Analyzer (ORA)) and a new recording tonometer with a convex apex designed for post-LASIK patients: the LASIK tonometer (CT), taking IOPcc IOP before surgery as the reference standard for IOP evaluations, instead of the usual Goldmann applanation tonometer (GAT) LASIK IOP values. When CT is applied towards a LASIK myopic cornea, it tightens the center of the corneal flap and a biomechanical response is observed, producing a pressure profile very similar to that existed before surgery. This is the first study to compare this effect with the air pulse from IOPcc as the gold standard before LASIK myopic surgery.

Barraquer Ophthalmology Center, Barcelona, Spain.

Prospective, double-masked study including n=72 eyes undergoing LASIK. IOP was measured before (pre) and 3 months after surgery (post) with CT, ORA (IOPcc and IOPg (Goldmann-correlated IOP)), and GAT. Intraclass correlation coefficient (ICC) and Bland-Altman (B-A) plot were calculated to assess the agreement. To determine which factors explain the bias trend in the B-A analysis, multiple stepwise regression was used to relate the differences in IOP and the change in corneal characteristics from pre- to post- surgery. IOP values obtained with GATpre, CTpost and ORA in pre- and post-surgery, were correlated respectively with clinical characteristics (including corneal hysteresis (CH) and corneal resistance factor (CRF) from ORA).

CTpost vs IOPccPre showed moderate agreement (MD: 1.40 mmHg, p = 0.004; limits of agreement:(LoA): –5.87 to 8.69). Larger differences were observed for CTpost vs IOPccPost (MD: 3.49 mmHg, p < 0.001; LoA: –1.99 to 8.98). CTpost vs GATpre showed minimal bias (MD: –0.236 mmHg, p = 0.342 ; LoA: –4.22 to 3.75). No correlation was found for CTpost vs IOPccPre (ICC = 0.24, 95% CI:(-0.02 - 0.46)(15.76 ± 2.61 vs 14.36 ± 3.36; p<0.074); or vs IOPccPost (ICC = 0.3, 95% CI: (0.12 - 0.48)(15.76 ± 2.61 vs 12.27 ± 2.10; p<0.004). CTpost had good correlation with GATpre (ICC = 0.74, 95% CI: 0.62 - 0.85 (15.76 ± 2.60 vs 16 ± 2.96; p <0.000). IOPccPost correlated with CH (r = –0.45, p <0.001); CTpost with CH (r = 0.34, p <0.001) and CRF (r = 0.54, p <0.001).

These findings highlight that while the CT displays no systematic bias relative to GATpre​, it shows clinically relevant deviations when compared with IOPcc both before and after surgery. CT and IOPcc captured distinct biomechanical aspects of the postoperative myopic LASIK cornea: CT reflects residual load-bearing rigidity, whereas IOPcc reflects biomechanical weakening. Still, CT may serve as an appropriate alternative to GAT in post-refractive LASIK myopic eyes.