Changes in intraocular pressure values measured with noncontact tonometer (NCT), ocular response analyzer (ORA) and corvis scheimpflug technology tonometer (CST) in the early phase after small incision lenticule extraction (SMILE)

Abstract

BackgroundCorneal biomechanical properties are always compromised after corneal refractive surgeries thus leading to underestimated intraocular pressure (IOP) that complicates the management of IOP. We investigated the changes in postoperative baseline of IOP values measured with noncontact tonometer (NCT), ocular response analyzer (ORA) and corvis scheimpflug technology (CST) in the early phase after small incision lenticule extraction (SMILE).MethodsTwenty-two eyes (−6.76 ± 1.39D) of 22 moderate and high myopes, (28.36 ± 7.14 years, 12 male and 10 female) were involved in this prospective study. IOP values were measured using a non-contact tomometer (NCT-IOP), an ocular response analyzer (corneal-compensated IOP, IOPcc and Goldmann-correlated IOP, IOPg) and a Corvis scheimpflug technology tonometer (CST-IOP) preoperatively, at 20 min and 24 h, postoperatively. Repeated measures analysis of variance (RM-ANOVA), Pearson’s correlation analysis and multiple linear regression models (stepwise) were performed. Cut-off P values were 0.05.ResultsExcept for IOPcc, NCT-IOP, IOPg, and CST-IOP values significantly decreased after SMILE procedure (All P values <0.05). ΔCCT, as well as ΔMRSE and ΔKm, did not significantly correlated with ΔNCT-IOP, ΔIOPcc, ΔIOPg or ΔCST-IOP, (all P values >0.05). Multiple linear regression models (stepwise) showed that the practical post-operative IOP value was the main predictor of the theoretical post-operative NCT-IOP, IOPcc and IOPg values (all P values <0.001). The postoperative applanation time 1 (AT1) value (B = 8.079, t = 4.866, P < 0.001), preoperative central corneal thickness (CCT) value (B = 0.035, t = 2.732, P = 0.014) and postoperative peak distance (PD) value (B = 0.515, t = 2.176, P = 0.043) were the main predictors of the theoretical post-operative CST-IOP value.ConclusionsIOP values are underestimated when assessed after SMILE by using NCT-IOP, IOPg and CST-IOP. The practical postoperative IOPcc value and theoretical post-operative CST-IOP value may be more preferable for IOP assessment in the early phase after SMILE.Trial registrationCurrent Controlled Trials ChiCTRONRC13003114. Retrospectively registered 17 March 2013

<p>A Review on Different Tonometers for Intraocular Pressure Measurement After Photorefractive Keratectomy or Small Incision Lenticule Extraction</p>

“…46,47 Shen demonstrated an insignificant change in peak distance, applanation time at the highest concavity, the second applanation time, the first applanation length, and the second applanation length in post 1 day SMILE eyes. 42 A significant increase in deformation amplitude was reported in post SMILE eyes by Shen, Pedersen, Mastropasqua and Fernandez. 42,[45][46][47] Yu demonstrated that in eyes performed with SMILE, the surrounding cornea would move slightly forward and the central posterior cornea would move slightly backward and return to normal gradually.…”

“…There were 32 articles investigated in the use of tonometers or biomechanical properties of cornea in post PRK eyes and 11 articles investigated in the use of tonometers or biomechanical properties of cornea in post SMILE eyes. 38,[40][41][42][43][44][45][46][47][48][49] Photorefractive Keratectomy…”

“…49 For CCT, Li and Shen demonstrated a significant reduction in post SMILE eyes. 41,42 For flat keratometry, steep keratometry, mean keratometry, Li demonstrated a significant reduction in 1 month, 3 months and 6 months after SMILE when compared with pre-operation. 41 Both Fu and Pedersen have found an insignificant difference in the first applanation time, deformation amplitude of corneal apex at highest concavity phase.…”

“…41 Another study by Shen showed a similar result of the IOP by noncontact tonometer, having a significant decrease in measured IOP after the SMILE procedure. 42 Noncontact Tonometry versus Other Tonometers When compared with bIOP by Corvis ST, IOP by noncontact tonometer showed a greater reduction in measured IOP in eyes at 1 month and 3 months after SMILE. It has a smaller reduction when compared with Goldmann corrected IOP and cornea compensated IOP by ocular response analyzer at 1 week, 1 month and 3 months after SMILE.…”

“…[40][41][42][45][46][47][48][49] Hosny, Li and Shen demonstrated a significant decrease in corneal hysteresis and corneal resistance factor in post SMILE eyes when compared with preoperative eyes. [40][41][42] Pedersen demonstrated that CH and CRF in post SMILE eyes were significantly lower when compared with healthy eyes by ocular response analyzer. 45 However, the study by Fu only showed a significant decrease in corneal resistance factor but an insignificant change in corneal hysteresis when comparing post SMILE eyes with pre-SMILE eyes.…”