New Algorithm for Measuring Intraocular Pressure Before and After Refractive Surgery
Authors: KJ Chen, A Joda, R Vinciguerra, A Eliasy, SMM Sefat, D Kook, B Geraghty, CJ Roberts, and A Elsheikh
Journal: Journal of Cataract & Refractive Surgery
Publication Date: May 2018
Correlation between CCT and IOP measured by the Goldmann applanation tonometer, the dynamic Scheimpflug analyser, and bIOP for (a) postoperative and (b) preoperative LASIK group (* = × [times sign]; bIOP = biomechanically corrected intraocular pressure; CCT = central corneal thickness; CVS-IOP = Scheimpflug analyser intraocular pressure; GAT-IOP = Goldmann applanation tonometry intraocular pressure; IOP = intraocular pressure; LASIK = laser in situ keratomileusis).
Summary:
The measurement of intraocular pressure (IOP) is important for identifying individuals at risk of glaucoma. The standard tonometer used in clinics is the Goldmann applanation tonometer. However, this method has limitations and can underestimate or overestimate IOP in eyes with thin or thick corneas, respectively. The error margin of Goldmann IOP has been estimated to affect more than 20% of patients.
Our study aimed to evaluate a new IOP measurement method called the biomechanically corrected intraocular pressure (bIOP) algorithm. The algorithm was developed to reduce the dependence of IOP measurements on corneal thickness and stiffness. The bIOP algorithm was tested in patients undergoing laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE) surgeries to correct refractive errors in myopia or myopic astigmatism.
The study comprised 14 patients in the LASIK group and 22 patients in the SMILE group. Preoperative and postoperative IOP measurements were taken using Goldmann applanation tonometry, Scheimpflug tomography, and the dynamic Scheimpflug analyser (Corvis ST) with bIOP algorithm. The preoperative Goldmann IOP and Scheimpflug analyser IOP values showed a significant positive correlation with central corneal thickness (CCT). However, no significant correlation was found between bIOP and CCT.
After both surgeries, there were significant decreases in Goldmann IOP and Scheimpflug analyser IOP values, whereas bIOP did not differ significantly. This finding shows that the bIOP algorithm can effectively reduce the correlation between CCT and IOP readings before and after LASIK and SMILE. The study also confirms the accuracy of the bIOP algorithm, which produces IOP estimates that are largely independent of CCT and the cornea's biomechanical properties.
Our findings suggest that the bIOP algorithm is a promising new method for measuring IOP that can reduce the error margin of Goldmann applanation tonometry. The bIOP algorithm is also effective after LASIK and SMILE surgeries, which are known to reduce corneal thickness and affect corneal biomechanics. This new method of IOP measurement could help to identify individuals at risk of glaucoma more accurately and reduce the number of false positives and false negatives in glaucoma risk profiling.