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Repeatability of a Scheimpflug tonometer to measure biomechanical parameters before and after myopic refractive
Nan-Ji Lu1, Farhad Hafezi, Jos J Rozema
1From the School of Ophthalmology and Optometry, Wenzhou Medical University, Wenzhou, Zhejiang, China (Lu, F. Hafezi, Zhang); Faculty of Medicine and Health Sciences, University of Antwerp, Wilrijk, Belgium (Lu, Rozema, N. Hafezi, Koppen); Department of Ophthalmology, Antwerp University Hospital, Edegem, Belgium (Lu, Rozema, N. Hafezi, Koppen); ELZA Institute, Dietikon, Switzerland (Lu, F. Hafezi, Hillen, N. Hafezi); Ocular Cell Biology Group, Center for Applied Biotechnology and Molecular Medicine, University of Zurich, Zurich, Switzerland (F. Hafezi); Department of Ophthalmology, University of Southern California, Los Angeles, California (F. Hafezi); Faculty of Medicine, University of Geneva, Geneva, Switzerland (F. Hafezi).
Purpose:
To assess the repeatability of several corneal biomechanical parameters with a Scheimpflug tonometer (Corvis ST) in myopic eyes and eyes that underwent transepithelial photorefractive keratectomy (transPRK), small-incision lenticule extraction (SMILE), or femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery.
Setting:
Eye Hospital of Wenzhou Medical University, Wenzhou, China.
Design:
Prospective randomized controlled study.
Methods:
315 eyes from 315 patients (135 myopes, 58 post-transPRK, 52 post-SMILE, and 70 post-FS-LASIK) were included. 3 consecutive scans were performed to evaluate the repeatability of the 40 parameters examined.
Results:
315 eyes were included. In all eyes, the coefficient of variation (CoV) for intraocular pressure (IOP) and biomechanical-corrected IOP (bIOP) ranged from 7.29% to 9.47% and 6.11% to 7.75%, respectively; the CoV of pachymetry was <0.8%. The intraclass correlation coefficient of Corvis Biomechanical Index-Laser Vision Correction (LVC) was 0.680 for post-transPRK, 0.978 for post-SMILE, and 0.911 for post-FS-LASIK. The CoV of Stress-Strain Index (SSI) was 204.93% for post-transPRK, 91.92% for post-SMILE, and 171.72% for post-FS-LASIK. The CoV of the 6 clinically important dynamic corneal response parameters ranged from 2.0% to 7.8% for myopia, 1.8% to 11.1% for post-transPRK, 2.1% to 8.7% for post-SMILE, and 1.8% to 8.8% for post-FS-LASIK.
Conclusions:
Excellent intrameasurement repeatability of IOP, bIOP, and pachymetry was observed in all groups; SSI measurement in post-LVC corneas displayed more variation. Caution is warranted when assessing SSI in post-LVC corneas for the purpose of diagnosing iatrogenic ectasia or evaluating biomechanical remodeling of postoperative refractive corneas.
