Intraocular pressure changes following LASER corneal refractive surgery: from true change to induced bias - a systematic review

Abstract

Topic: LASER corneal refractive surgery can bias intraocular pressure (IOP) measurements. We aimed to assess the effect each surgery has on IOP and to analyze how different tonometers behave postoperatively. Therefore, mean IOP change after surgery per surgical technique and per tonometry method was our main outcome. Clinical relevance: While Goldmann Applanation Tonometry (GAT) remains the gold standard for tonometry, its dependence on corneal structure poses limitations. To address this, we explored different tonometry methods which could improve the accuracy of IOP measurement in patients that underwent corneal refractive surgery. Methods: A literature search was conducted until October 17th 2022 through PubMed, Embase, Web of Science and Scopus. Eligible studies included patients that had undergone LASER corneal refractive surgery, had to be free of other ophthalmological disorders/corneal irregularities/ocular hypotensive medications, and IOP had to be measured pre- and postoperatively. Risk of bias was evaluated using the NIH assessment tool for before-after studies with no control group. Results: 92 articles were included, encompassing 12 surgery techniques and 20 tonometry methods. Almost all studies (n=85, 92.4%) reported a significant difference between pre- and postoperative IOP. The mean IOP change was -2.56 ± 2.00 mmHg (-16.6 ± 12.9% from baseline). SMILE was responsible for the largest change (-3.56 ± 2.04 mmHg), while goldmann-correlated IOP by ORA was the tonometer with the highest decrease (-4.69 ± 1.33 mmHg). Furthermore, GAT IOP was overall lower when compared to other tonometers, especially cornea-compensated IOP (ccIOP) by ORA, Dynamic Contour Tonometry (DCT) and biomechanically corrected IOP (bIOP) by Corvis-ST. Conclusion: Regarding limitations, some surgeries/tonometers were represented only in a few studies and lack of blinding and small sample size may have introduced bias. Future studies are needed to draw significant conclusions. In conclusion, alongside the gold standard GAT, newer tonometers (ORA's ccIOP, DCT and Corvis-ST's bIOP) may offer more consistent measurements and be less susceptible to surgically induced variations in corneal biomechanics. This should be considered when measuring IOP post-surgery, especially regarding glaucoma patient care.