Corvis ST Tonometer Research Articles

Corneal biomechanics: Corvis® ST parameters after LASIK

Corneal refractive surgery alters the biomechanical properties of the cornea. This study was initiated to evaluate corneal biomechanical parameters after LASIK using a Corvis® ST tonometer (CST). This retrospective study included 51 eyes of 32 myopic patients. All CST measurements were performed 1 day before surgery and at the 1-month follow-up examination. The LASIK procedure included mechanical flap preparation using a Moria SBK microkeratome and an Allegretto excimer laser platform. Statistically significant differences were observed for mean second applanation length, mean first and second deflection lengths, mean first and second deflection amplitudes, peak distance and radius of curvature. Statistically significant positive correlations were found between the change (Δ) in radius of curvature and Δ in manifest refraction spherical equivalent (MRSE), between the ablation depth and the Δ in intraocular pressure. Applying multiple regression models also revealed statistically significant differences in parameters obtained by CST measurements. Several CST parameters were statistically significantly altered by LASIK thereby indicating that flap creation, ablation or both, significantly change the ability of the cornea to absorb or dissipate energy.

Effects of laser in situ keratomileusis (LASIK) on corneal biomechanical measurements with the Corvis ST tonometer.

PurposeThis study was initiated to evaluate biomechanical changes using the Corvis ST tonometer (CST) on the cornea after laser in situ keratomileusis (LASIK).SettingUniversity Medical Center Hamburg-Eppendorf, Germany, and Care Vision Refractive Centers, Germany.DesignRetrospective cohort study.MethodsThis retrospective study included 37 eyes of 37 refractive patients. All CST measurements were performed 1 day before surgery and at the 1-month follow-up examination. The LASIK procedure included mechanical flap preparation using a Moria SBK microkeratome and an Allegretto excimer laser platform.ResultsStatistically significant differences were observed for mean first applanation length, mean first and second deflection lengths, mean first and second deflection amplitudes, radius of curvature, and peak distance. Significant positive correlations were found between the change (Δ) of radius of curvature and manifest refraction spherical equivalent (MRSE), ablation depth, and Δintraocular pressure as well as between AD and ΔHC-time. Each diopter of myopic correction in MRSE resulted in an increase in Δradius of curvature of 0.2 mm.ConclusionSeveral CST parameters were statistically significantly altered by LASIK, thereby indicating that flap creation, ablation, or both, significantly change the ability of the cornea to absorb or dissipate energy.

Scheimpflug camera in the quantitative assessment of reproducibility of high-speed corneal deformation during intraocular pressure measurement.

The paper presents an original analysis method of corneal deformation images from the ultra-high-speed Scheimpflug camera (Corvis ST tonometer). Particular attention was paid to deformation frequencies exceeding 100 Hz and their reproducibility in healthy subjects examined repeatedly. A total of 4200 images with a resolution of 200 × 576 pixels were recorded. The data derived from 3 consecutive measurements from 10 volunteers with normal corneas. A new image analysis algorithm, written in Matlab with the use of the Image Processing package, adaptive image filtering, morphological analysis methods and fast Fourier transform, was proposed. The following results were obtained: (1) reproducibility of the eyeball reaction in healthy subjects with precision of 10%, (2) corneal vibrations with a frequency of 369 ± 65 Hz (3) and amplitude of 7.86 ± 1.28 µm, (4) the phase shift within two parts of the cornea of the same subject of about 150°. The result of image sequence analysis for one subject and deformations with a corneal frequency response above 100 Hz.

Comparison of Corvis ST Tonometer to Other Tonometers and Clinical Usefulness of Corvis ST Tonometer

Comparison of Corvis ST Tonometer to Other Tonometers and Clinical Usefulness of Corvis ST Tonometer