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

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.