Open AccessSystematic Review Underestimation of Intraocular Pressure (IOP) After LASIK and PRK: Systematic Review and Meta-Analysis by Stamatios Lampsas Stamatios Lampsas SciProfiles Scilit Preprints.org Google Scholar 1,*, Efthymios Karmiris Efthymios Karmiris SciProfiles Scilit Preprints.org Google Scholar 1, George D. Kymionis George D. Kymionis SciProfiles Scilit Preprints.org Google Scholar 2 Irini Chatziralli Irini Chatziralli SciProfiles Scilit Preprints.org Google Scholar 1 1 2nd Department of Ophthalmology, Attikon University Hospital, Medical School, National and Kapodistrian University of Athens, 11528 Athens, Greece 2 1st Department of Ophthalmology, “G. Gennimatas” Hospital, Medical School, National and Kapodistrian University of Athens, 11528 Athens, Greece * Author to whom correspondence should be addressed. J. Clin. Med. 2026, 15(12), 4426; https://doi.org/10.3390/jcm15124426 (registering DOI) Submission received: 13 April 2026 / Revised: 3 June 2026 / Accepted: 5 June 2026 / Published: 8 June 2026 Abstract Background/Objectives: Refractive corneal surgery alters corneal biomechanics and thickness, affecting the accuracy of intraocular pressure (IOP) measurements. This systematic review and meta-analysis aimed to quantify the postoperative underestimation of IOP following such procedures. Methods: This systematic review and meta-analysis, conducted based on PRISMA guidelines, evaluated pre- and postoperative IOP changes following LASIK and PRK using GAT, ORA, and CORVIS ST, based on studies identified through PubMed, Scopus, Cochrane Library, and ScienceDirect up to 31 December 2025, with results synthesized using random-effects models and reported as mean differences (MD) with 95% confidence intervals (CI). Results: Of the 1796 articles identified, 54 studies met the inclusion criteria, encompassing a total of 4730 eyes. After LASIK, a statistically significant underestimation of IOP was observed with all methods: GAT (MD: 3.23 mmHg, 95% CI: 2.77–3.69, p < 0.001), ORA (MD: 2.13 mmHg, 95% CI: 1.56–2.70, p < 0.001), and CORVIS ST (MD: 1.39 mmHg, 95% CI: 0.53–2.24, p = 0.001). Similarly, after PRK, a significant reduction in IOP was recorded with GAT (MD: 2.04 mmHg, 95% CI: 1.24–2.84, p < 0.001) and ORA (MD: 2.46 mmHg, 95% CI: 0.62–4.29, p < 0.01), while the difference measured by CORVIS ST was not statistically significant. Conclusions: LASIK and PRK result in systematic underestimation of IOP, most pronounced with GAT and less evident with ORA and CORVIS ST, highlighting the importance of selecting appropriate tonometry methods for accurate monitoring, especially in patients at risk of glaucoma or elevated IOP. Keywords: corneal biomechanics; intraocular pressure; LASIK; PRK; refractive surgery Accurate measurement of IOP is a critical component of the ophthalmologic examination for the detection and monitoring of glaucoma, with Goldmann applanation tonometry (GAT) considered the gold standard among the various available tonometry methods [ 4]. Refractive corneal surgeries, such as Laser-Assisted In Situ Keratomileusis (LASIK) and Photorefractive Keratectomy (PRK), reduce central corneal thickness by removing tissue from the anterior stroma—the strongest layer—thereby altering biomechanical properties, decreasing overall stability, and weakening corneal rigidity, elasticity, and viscoelastic response [ 5, 6]. The accuracy of intraocular pressure measurements may be significantly affected following these procedures due to alterations in the biomechanical properties of the cornea, thereby increasing the risk of underestimation and potentially resulting in delayed diagnosis of ocular hypertension and/or glaucoma [ 7, 8]. Previous studies have shown that IOP is frequently underestimated after LASIK and PRK. Postoperative corneal thinning and alterations in corneal biomechanics reduce resistance during applanation tonometry, leading to lower measured IOP values. This underestimation may delay the detection and management of steroid-induced IOP elevation and has been associated with progression to advanced glaucoma [ 9, 10]. However, contemporary devices such as the Ocular Response Analyzer (ORA) and Corneal Visualization Scheimpflug Technology (Corvis ST) enable more accurate estimation of IOP despite post-refractive alterations in corneal biomechanics, offering a comparative advantage over GAT [ 7, 10, 11, 12]. Although these novel devices offer several advantages, the underestimation of IOP still exists and newer algorithms adapted both for Corvis ST and ORA have tried to improve this, with limited efficiency and accuracy [ 13]. Given the increasing number of patients undergoing refractive surgery worldwide and the critical role of accurate IOP assessment in glaucoma detection and monitoring, understanding the extent of postoperative IOP underestimation carries important clinical significance and was a major motivation for conducting this study. Based on the above, the aim of this systematic review and meta-analysis is to evaluate the changes in IOP following corneal refractive surgeries in patients who have undergone LASIK and PRK. Secondarily, the study seeks to quantify these changes through meta-analysis, focusing on measurements obtained with GAT, the ORA and Corvis ST before and after surgery, as well as their relationship with alterations in corneal biomechanics. 3. Results 3.1. Search Results A total of 54 studies were included in the systematic review and meta-analysis following the screening of 1796 initially identified records. Overall, 4730 eyes undergone refractive surgery were included, with a mean subject’s age of 32.7 ± 7.8 years, 45.3% of them being male, and a mean post refractive surgery follow-up time 4.3 months (, ). 3.2. Comparison of Pre- and Post-Operative IOP in Patients Who Have Undergone LASIK 3.2.1. Measurement of Pre- and Post-Operative IOP Using a Goldmann Applanation Tonometer (GAT) After LASIK In the present analysis, 36 studies were included, examining a total of 2724 eyes before and after LASIK. This meta-analysis demonstrated a statistically significant difference in IOP measured with GAT, with a calculated mean difference of 3.23 mmHg (95% CI: 2.77–3.69, p < 0.001). Heterogeneity among the included studies was substantial, with I 2 = 96% (). In sensitivity analysis, a total of 30 studies were included, encompassing 2166 eyes evaluated before and after LASIK, six outlier studies were removed after funnel plot assessment. The findings of this analysis revealed a statistically significant decrease in IOP measured with GAT, with an estimated mean difference of 3.45 mmHg (95% CI: 3.18–3.72, p < 0.001). The level of heterogeneity across the included studies was moderate as indicated by an I 2 value of 69% (). Egger’s test did not indicate significant publication bias, as the intercept was not statistically significant ( p = 0.495). 3.2.2. Measurement of Pre- and Post-Operative IOP Using Ocular Response Analyzer (ORA) After LASIK A total of 17 studies were included in this analysis, encompassing 847 eyes evaluated before and after LASIK. The meta-analysis revealed a statistically significant decrease in IOP measured with ORA, with an estimated mean difference of 2.13 mmHg (95% CI: 1.56–2.70, p < 0.001). Substantial heterogeneity was observed among the included studies, with an I 2 value of 83% (). In this analysis, 14 studies were included, comprising a total of 706 eyes evaluated before and after LASIK, three outlier studies were removed after funnel plot assessment. The meta-analysis demonstrated a statistically significant reduction in IOP measured with ORA, with a calculated mean difference of 2.17 mmHg (95% CI: 1.92–2.42, p < 0.001). The heterogeneity among the included studies was moderate, with an I 2 value of 73% (). No evidence of publication bias was detected by Egger’s test, as the intercept did not reach statistical significance ( p = 0.649). 3.2.3. Measurement of Pre- and Post-Operative IOP Using Corneal Visualization Scheimpflug Technology (Corvis ST) After LASIK A total of 9 studies were included in this analysis, encompassing 470 eyes assessed before and after LASIK. The meta-analysis revealed a statistically significant decrease in IOP measured with Corvis ST, with an estimated mean difference of 1.39 mmHg (95% CI: 0.53–2.24, p = 0.001). Substantial heterogeneity was observed among the included studies, with an I 2 value of 91% (). A total of 7 studies were incorporated into the sensitivity analysis, after two outlier studies removed, including 334 eyes evaluated before and after LASIK. The meta-analysis indicated a statistically significant reduction IOP measured with Corvis ST, with an estimated mean difference of 1.18 mmHg (95% CI: 0.61–1.76, p < 0.0001). Moderate heterogeneity was identified among the included studies (I 2 = 74%). Egger’s regression analysis was performed to assess potential publication bias and did not reveal statistically significant small-study effects (intercept = 3.61, 95% CI: −2.01 to 9.23, p = 0.159), suggesting no evidence of publication bias (). This systematic review and meta-analysis comprehensively evaluated the impact of refractive procedures, namely LASIK and PRK, on IOP measurements using three different tonometry technologies: GAT, ORA, and CORVIS ST. The findings suggest that both LASIK and PRK result in a statistically significant postoperative underestimation of IOP, with the magnitude of underestimation being smaller when measured with CORVIS ST, which, through Scheimpflug imaging, appears to underestimate IOP to a lesser extent. Similarly, in patients undergoing PRK, a statistically significant reduction in measured IOP was observed with GAT and ORA, with mean differences of 2.04 mmHg and 2.46 mmHg, respectively. Moreover, sensitivity analysis for GAT measurements after PRK demonstrated that the pooled effect estimates remained stable after exclusion of outlier studies, supporting the robustness of the observed postoperative IOP reduction despite the initial heterogeneity. In contrast, IOP measurements obtained with CORVIS ST after PRK did not demonstrate a statistically significant change, suggesting that this technology may be more resistant to corneal alterations induced by the procedure. However, these findings should be interpreted cautiously, as the analysis of Corvis ST after PRK included only a limited number of studies and eyes, reducing statistical power and increasing the possibility of a Type II error. Although PRK does not involve the creation of a corneal flap, changes in corneal structure and biomechanical properties appear sufficient to affect IOP measurements. Biomechanical simulation studies further indicate that LASIK alters corneal stress distribution, reducing its resistance to deformation and thereby increasing measurement error [ 70, 71]. This effect is more pronounced with deeper tissue ablation and thicker flaps and is more evident in LASIK compared to surface ablation techniques such as PRK. With regard to corneal biomechanical properties, accounting for their alterations may improve the accuracy of postoperative IOP assessment, with corneal hysteresis representing a key parameter for quantifying these changes. The cornea exhibits viscoelastic behaviour, meaning it possesses both viscous and elastic properties, similar to most biological tissues. Viscoelastic materials demonstrate a degree of hysteresis during deformation, reflecting their capacity to dissipate energy when subjected to external forces [ 72]. Corneal hysteresis represents the ability of corneal tissue to absorb and release energy during the process of bidirectional applanation and constitutes an important biomechanical property of the cornea [ 72]. It reflects the cornea’s capacity to dampen mechanical stress, the balance between its elastic and viscous components, and the overall structural integrity of the tissue [ 73]. Clinically, reduced corneal hysteresis has been associated with glaucoma progression, provides insight into corneal biomechanical stability and the risk of postoperative ectasia following LASIK, and is commonly decreased in keratoconus, contributing to the diagnosis and monitoring of the disease [ 74, 75 Similarly, the corneal resistance factor (CRF) is a parameter measured by ORA that reflects the overall resistance of the cornea to deformation, incorporating its viscoelastic properties [ 68, 76]. It is strongly correlated with central corneal thickness and overall corneal stiffness and is derived from the difference between inward and outward applanation pressures during air-puff–induced deformation [ 77, 78]. Following refractive procedures such as LASIK and PRK, both CRF and corneal hysteresis are significantly reduced, with a more pronounced decrease observed after LASIK compared to PRK, reflecting greater biomechanical weakening due to flap creation and deeper stromal ablation [ 79, 80, 81]. Moreover, recent evidence demonstrates that LASIK produces significantly greater reductions in both CH and CRF compared to PRK, reflecting additional biomechanical weakening from flap creation and deeper stromal ablation [ 82]. Finite element simulations confirm that LASIK concentrates stress in the posterior stroma while PRK maintains more uniform anterior stress distribution, directly explaining the greater IOP underestimation observed after LASIK. Newer technologies offer only partial correction, as a 2024 study found that Corvis ST’s bIOP remained stable after PRK (change: 0.3 ± 1.7 mmHg) while ORA’s IOPcc still decreased significantly (−1.6 ± 4.0 mmHg), and the two devices should not be used interchangeably [ 12]. Thus, integrating CH and CRF as central interpretive variables provides a more complete framework for understanding why even advanced tonometers offer only partial correction of post-refractive IOP measurement error. Finally, beyond the multifactorial nature of IOP measurement discussed above, a deeper understanding of how each tonometer’s operating principle influences post-refractive readings is essential for interpreting the observed differences between GAT, ORA, and Corvis ST. GAT measures IOP based on the force required to applanate a fixed corneal area, operating under the Imbert-Fick law that assumes an ideal spherical, thin, dry, and elastic cornea [ 83]. Refractive surgery violates these assumptions through corneal thinning, flattening, and altered biomechanics [ 84]. Consequently, GAT predominantly measures measurement-related bias rather than true IOP, as reduced thickness and increased deformability lower applanation force without any actual change in true IOP [ 84]. In contrast, ORA partly adjusts for biomechanical changes by assessing both inward and outward applanation pressures and deriving corneal hysteresis and corneal resistance factors, thereby providing a corneal-compensated IOP that may more accurately reflect true IOP compared with GAT [ 12]. Corvis ST further enhances assessment by employing an ultra-high-speed Scheimpflug imaging system to monitor dynamic corneal deformation, allowing estimation of a biomechanically adjusted IOP that incorporates individual differences in corneal stiffness and thickness through biomechanical modeling [ 85]. Thus, these devices differ in accuracy, with GAT showing the greatest bias, Corvis ST the least, and ORA demonstrating intermediate performance. Postoperative IOP measurements should therefore not be considered interchangeable. A limitation of this meta-analysis is the substantial heterogeneity observed across several analyses, likely due to differences in surgical techniques, corneal characteristics, and follow-up duration among studies. Additionally, subgroup analyses and meta-regression were limited by the inconsistent reporting of variables such as ablation depth and central corneal thickness. Furthermore, differences in postoperative follow-up duration may have contributed to the observed heterogeneity, as IOP measurements can vary over time after refractive surgery ( Supplementary Table S4). Another limitation of this meta-analysis is that physiological variability in IOP, including circadian fluctuations, body position, and recent diagnostic or therapeutic interventions, was not consistently reported across the included studies [ 86]. These factors may influence IOP measurements and could contribute to variability in postoperative assessments, particularly in post-refractive surgery patients where measurement accuracy is already affected by corneal alterations. Clinically, the findings of this meta-analysis are particularly relevant for patients with a history of refractive surgery who are being monitored for glaucoma or elevated intraocular pressure. However, the high heterogeneity observed across most analyses suggests that the results should be interpreted with caution. In glaucoma suspects, clinicians must integrate other diagnostic tools, including optic nerve evaluation, retinal nerve fiber layer imaging, and visual field testing, rather than relying solely on measured IOP values. Finally, despite the development of newer technologies providing biomechanically adjusted IOP measurements, such as ORA and Corvis ST, clinicians should remain aware of the potential underestimation of IOP after refractive surgery and perform a comprehensive ophthalmologic evaluation. This systematic review and meta-analysis comprehensively evaluated the impact of refractive procedures, namely LASIK and PRK, on IOP measurements using three different tonometry technologies: GAT, ORA, and CORVIS ST. The findings indicate that both LASIK and PRK lead to a statistically significant postoperative underestimation of IOP, with the magnitude showing differences among tonometry methods. Clinicians should be aware that even biomechanically adjusted IOP readings may underestimate true IOP post refractive surgery, warranting caution in glaucoma screening and monitoring. Supplementary Materials The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/jcm15124426/s1, Supplementary Table S1: PRISMA 2020 Checklist. Supplementary Table S2: Search queries regarding the changes of Intraocular pressure before and after Laser-Assisted In Situ Keratomileusis (LASIK) and Photorefractive Keratectomy (PRK) Refractive Surgery; Supplementary Table S3: Quality assessment results obtained using the Newcastle–Ottawa Quality Assessment Scale (NOS) tool; Supplementary Table S4: Baseline corneal characteristics of the included studies. Conceptualisation, S.L., E.K. and I.C.; methodology, S.L.; writing—original draft preparation, S.L., E.K., G.D.K. and I.C.; writing—review and editing, S.L., E.K., G.D.K. and I.C.; supervision, G.D.K. and I.C. 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[ Google Scholar] PRISMA flowchart for study selection. PRISMA flowchart for study selection. Characteristics and findings of the included studies. Characteristics and findings of the included studies. Study Eyes Refractive Method IOP Measurement Male Sex (%) Age (Yes) LASIK, Laser-Assisted In Situ Keratomileusis; PRK, Photorefractive Keratectomy; IOP, Intraocular Pressure; GAT, Goldmann Applanation Tonometry; CORVIS ST, Corneal Visualization Scheimpflug Technology. Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. © 2026 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license. Share and Cite Lampsas, S.; Karmiris, E.; Kymionis, G.D.; Chatziralli, I. Underestimation of Intraocular Pressure (IOP) After LASIK and PRK: Systematic Review and Meta-Analysis. J. Clin. Med. 2026, 15, 4426. https://doi.org/10.3390/jcm15124426 Lampsas S, Karmiris E, Kymionis GD, Chatziralli I. Underestimation of Intraocular Pressure (IOP) After LASIK and PRK: Systematic Review and Meta-Analysis. Journal of Clinical Medicine. 2026; 15(12):4426. https://doi.org/10.3390/jcm15124426 Lampsas, Stamatios, Efthymios Karmiris, George D. Kymionis, and Irini Chatziralli. 2026. "Underestimation of Intraocular Pressure (IOP) After LASIK and PRK: Systematic Review and Meta-Analysis" Journal of Clinical Medicine 15, no. 12: 4426. https://doi.org/10.3390/jcm15124426 Lampsas, S., Karmiris, E., Kymionis, G. D., & Chatziralli, I. (2026). Underestimation of Intraocular Pressure (IOP) After LASIK and PRK: Systematic Review and Meta-Analysis. Journal of Clinical Medicine, 15(12), 4426. https://doi.org/10.3390/jcm15124426 Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here. Article Metrics Article metric data becomes available approximately 24 hours after publication online.
Underestimation of Intraocular Pressure (IOP) After LASIK and PRK: Systematic Review and Meta-Analysis
