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Corneal Deformation Parameters Provided by the Corvis-ST Pachy-Tonometer in Healthy Subjects and Glaucoma Patients

Salvetat, Maria L. MD; Zeppieri, Marco MD, PhD; Tosoni, Claudia MD; Felletti, Mirella BSc; Grasso, Leonardo BSc; Brusini, Paolo MD

doi: 10.1097/IJG.0000000000000133
Original Studies

Purpose: To evaluate precision and accuracy of Corvis-ST, a new noncontact tonometer equipped with a high-speed Scheimpflug technology, which measures intraocular pressure (IOP), central corneal thickness (CCT), and corneal deformation parameters (CDPs). Relationships among IOP, CCT, and CDPs were also assessed.

Materials and Methods: This prospective, randomized study included 1 eye of 164 subjects (79 controls and 85 glaucoma patients), which underwent IOP measurements taken 3 times with Goldmann applanation tonometry (GAT) and Corvis-ST in random order. Precision was evaluated using intraclass correlation coefficients. Intermethod agreement was assessed using Bland-Altman method. Relationships amongst IOP, CCT and CDPs were evaluated using linear regression analysis.

Results: Corvis-ST intraclass correlation coefficients ranged between 0.95 and 0.99 for IOP and CCT; between 0.17 and 0.97 for CDPs. Mean (GAT−Corvis-ST) IOP was 1.4±2.7 mm Hg, which appeared related to IOP and CDPs (P<0.05). CDPs significantly differed between glaucoma patients and controls (P<0.05). GAT and Corvis-ST IOP was related to CCT (P<0.05) and CDPs (P<0.001).

Conclusions: Corvis-ST precision was excellent for IOP and CCT; moderate for CDPs. Corvis-ST underestimated GAT IOP, especially at higher IOP and at lower corneal deformability levels. GAT and Corvis-ST IOP increased in thicker and less deformable corneas. Glaucoma patients showed significantly less deformable corneas than controls.

Department of Ophthalmology, Azienda Ospedaliero-Universitaria, “Santa Maria della Misericordia,” Udine, Italy

Disclosure: The authors declare no conflict of interest.

Reprints: Paolo Brusini, MD, Department of Ophthalmology, Azienda Ospedaliero-Universitaria “Santa Maria della Misericordia”, p.le “Santa Maria della Misericordia” n.15, 33100, Udine, Italy (e-mail:

Received May 8, 2013

Accepted August 22, 2014

Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.