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Corvis® ST

Evaluation of corneal biomechanical response, tonometry and pachymetry

  • Biomechanical corrected IOP (bIOP)
  • Effect of corneal crosslinking
  • Improved prediction of refractive outcome
  • Early keratoconus detection (CBI)
  • Glaucoma risk factor
  • Glaucoma treatment
  • Highlight
  • Functions
  • Biomechanical Properties
  • Videos
  • FAQ
  • Technical Data
  • Contact

Corneal Visualization Scheimpflug Technology

The revolutionary Corvis® ST records the reaction of the cornea to a defined air pulse using a newly developed high-speed Scheimpflug camera. This camera captures over 4 300 images per second, permitting highly precise measurement of IOP and corneal thickness. Based on a video of 140 images, taken within 31 ms after onset of the air pulse, the Corvis® ST provides a detailed assessment of corneal biomechanical properties.
The information obtained on the biomechanical response of the cornea is used to calculate a biomechanically corrected IOP (bIOP). Furthermore it allows ectatic diseases such as keratoconus to be detected at a very early stage. Biomechanical properties also play an important role in the development and progression of glaucoma.

OCULUS Corvis® ST

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Corvis® ST and Pentacam®

The Tomographic Biomechanical Index, or TBI, provides a unique combined expression of Corvis ST and Pentacam measurement data.

Corvis® ST and Pentacam®

The Tomographic Biomechanical Index, or TBI, provides a unique combined expression of Corvis ST and Pentacam measurement data.

NEW: Now with even
greater precision!

Your benefits:

  • Ectasia risk assessment now even more reliable
  • Reasoned selection of the optimal treatment
  • AI helps save time
  • Well-informed patient selection raises surgical throughput
THE SOLUTION FOR
REFRACTIVE SURGEONS

Find the best procedure for each and every patient
with the TBI guide for refractive surgery

Developed by Prof. Ambrósio

TBI Skala

Functions

Screening Trockenes Auge - In nur 5 Minuten zum schnellen Überblick - Die Ergebnisse des Screenings werden übersichtlich auf dem Bildschirm dargestellt
bIOP/CCT measurements
IOP-follow-up
Pachymetric progression
Biomechanicsl response video

IOP/Pachy Display

Biomechanically corrected IOP (bIOP)

bIOP readings are less dependent on biomechanical properties and corneal thickness and hence more accurate than IOP readings. The data are easy to read and interpret, and the IOP follow-up chart is neatly arranged.

IOP correction is based on corneal thickness, age and the biomechanical response of the cornea. When calculated this way bIOP is less influenced by corneal properties and thickness than it is with other measurement methods. As the Corvis® ST measures both biomechanical response and corneal thickness with high precision, the device is able to correct for both factors at the same time.

Due to the measurement principle, it delivers bIOP values uninfluenced by the tear film. This and the fast auto tracking and auto release ensure highly repeatable, user-independent IOP and thickness readings.

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Screening Trockenes Auge - In nur 5 Minuten zum schnellen Überblick - Die Ergebnisse des Screenings werden übersichtlich auf dem Bildschirm dargestellt
Biomechanical response video
Normal ranges of dynamic corneal response (DCR) parameters
Standard deviation for screening parameters
Corvis Biomechanical Index (CBI)
Screening Trockenes Auge - In nur 5 Minuten zum schnellen Überblick - Die Ergebnisse des Screenings werden übersichtlich auf dem Bildschirm dargestellt
Screening Trockenes Auge - In nur 5 Minuten zum schnellen Überblick - Die Ergebnisse des Screenings werden übersichtlich auf dem Bildschirm dargestellt
Screening Trockenes Auge - In nur 5 Minuten zum schnellen Überblick - Die Ergebnisse des Screenings werden übersichtlich auf dem Bildschirm dargestellt

Vinciguerra Screening Report &
Biomechanical Keratoconus Detection with the CBI

Corvis Biomechanical Index (CBI)

This module provides comprehensive biomechanical screening and keratoconus detection.
The software displays the patient’s results against normative values in easy-to-grasp charts.

The Vinciguerra Screening Report allows fast and comprehensive screening for corneas with abnormal corneal biomechanical properties. It is the first available screening software that combines biomechanical information with pachymetric progression data. It calculates the Corvis Biomechanical Index (CBI), which enables the detection of ectatic corneas based on these findings. As keratoconus is caused by biomechanical changes and leads to progressive thinning, the software is able to detect the earliest signs of this disease.

Furthermore, the normal ranges of dynamic corneal response (DCR) parameters are shown as a function of bIOP and time. Standardized parameters indicate whether the cornea has a normal biomechanical response.

The grey boxes show for each screening parameter how many standard deviations (SD) the parameter deviates from the mean of healthy patients. Positive values indicate softer tissue, negative values stiffer tissue than in the average healthy patient.

White area: within ± 1 SD
Light grey: between 1 – 2 SD
Dark grey: more than 2 SD

Stress-strain curves describe the elastic properties of the cornea. The curves are shifted to the right if the cornea is soft and to the left if the cornea is stiff. The stress-strain index (SSI) describes the position of the curve. A value of 1 indicates the average elasticity of a healthy 50-year-old patient. A value smaller than 1 indicates a softer and a value greater than 1 a stiffer than average behaviour.

The Corvis Biomechanical Index (CBI) is based on a logistic regression approach and was developed to detect keratoconus at an early stage. It is based on five Dynamic Corneal Response parameters and gives a score from 0 (low ectasia risk) to 1 (high ectasia risk).

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Screening Trockenes Auge - In nur 5 Minuten zum schnellen Überblick - Die Ergebnisse des Screenings werden übersichtlich auf dem Bildschirm dargestellt
Screening values in comparison to populations of healthy (green) and keratoconic (red) patients
Tomographic Biomechanical Index (TBI)
Belin / Ambrósio D value(Pentacam®)
4 Maps Refractive (Pentacam®)
Screening Trockenes Auge - In nur 5 Minuten zum schnellen Überblick - Die Ergebnisse des Screenings werden übersichtlich auf dem Bildschirm dargestellt
NEW: Selection of the reference database (global or East Asian patients)
Selection of database (untreated or post-LVC)
Normative data for DCR parameters for stable (green) post-LVC or post-LVC ectasia cases (red)

Tomographic and Biomechanical Assessment

Tomographic Biomechanical Index (TBI)

Integration of Pentacam® data for a combined tomographic and biomechanical analysis. The best of two worlds:

TBI is calculated using an artificial intelligence approach to optimize ectasia detection.

By combining tomographic data from the Pentacam® with biomechanical data from the Corvis® ST one can further improve sensitivity and specificity in the detection of patients with a significant risk for developing ectasia after refractive surgery. The outcome of this analysis is supplied by the Tomographic Biomechanical Index (TBI). This index together with the comprehensive display helps you to avoid risks and to treat more patients safely.

New CBI-LVC

The CBI-LVC measures biomechanical stability after laser vision correction. This information is key for making clinical decisions such as on retreatments after LASIK or corneal crosslinking in case of ectasia.

Various preoperatively screening methods are available for analyzing the risk for developing ectasia after laser vision correction. However, the possibilities for postoperatively evaluating ectasia risk based on objective criteria are still limited to date.

This software allows automatic assessment of postoperative biomechanical stability. The normative data for stable post-op cases are represented by the green curves, while the red curves represent post-LVC ectasia cases.

Treated corneas are automatically recognized as such and analyzed against post-LVC normative data. Alternatively the user can manually select the option of analyzing a treated cornea.

As its final output the CBI-LVC estimates a patient’s risk of developing ectasia after laser surgery.

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Screening Trockenes Auge - In nur 5 Minuten zum schnellen Überblick - Die Ergebnisse des Screenings werden übersichtlich auf dem Bildschirm dargestellt
See the change of the data compared to a baseline exam
Superimposition of the biomechanical response videos of measurement A (red) and measurement B (blue)
Stress-strain behaviour for all selected exams
Keratoconus staging (E-Staging) based on biomechanical response
Time of crosslinking procedure

BEST Display

Homburg Biomechanical E-STaging Display: quantification of early biomechanical changes

Detecting biomechanical changes over time: Keratoconus progression and early signs of improvement after corneal crosslinking can only be detected by visualization and quantification of biomechanical changes.

Visualization and quantification of biomechanical changes over time is an essential precaution in various clinical applications. Progression of keratoconus must be detected at a very early stage if a severe loss of vision is to be prevented.

Another important feature is to verify the success of treatment after corneal crosslinking. Whereas topographic changes only occur after several months, biomechanical changes can be measured with the Corvis ® ST already four weeks after the procedure.

The BEST Display is the ideal solution for monitoring biomechanical changes over time. It enables you to analyze the progression, related to a baseline measurement.

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Screening Trockenes Auge - In nur 5 Minuten zum schnellen Überblick - Die Ergebnisse des Screenings werden übersichtlich auf dem Bildschirm dargestellt
IOP follow-up
bIOP/CCT measurements
Distribution of BGF in healthy eyes (green) and NTG patients (red). The black line shows the BGF-output for this patient.
Output of the Biomechanical Glaucoma Factor (BGF)

Glaucoma Screening Software

Biomechanical Glaucoma Factor (BGF)

Detecting normal tension glaucoma (NTG) is very challenging in clinical practice. Intraocular pressure measurement will not indicate any elevated risk for glaucoma, and the optic nerve head might also appear relatively normal.

It recently has been shown that biomechanical properties can serve as an independent risk indicator for NTG. This provided the basis for the development of the Biomechanical Glaucoma Factor (BGF).2

The BGF is a very early risk indicator of NTG which will guide you to the best clinical decisions for your patient.

2 Pillunat KR, et al. A new biomechanical glaucoma factor to discriminate normal eyes from normal pressure glaucoma eyes. Acta Ophthalmol. 2019 Nov;97(7):e962-e967. doi: 10.1111/aos.14115. Epub 2019 Apr 24. PMID: 31016882

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Further functions

DCR: Dynamic Corneal Response

The DCR Display gives you various insights into the biomechanical properties of the cornea. The software provides detailed analysis of the Scheimpflug images taken during deformation of the cornea. The parameters which describe the deformation characteristics give information about corneal biomechanics. Also included are the Corvis Biomechanical Index (CBI) and Tomographic Biomechanical Index (TBI).

Emailing videos to patients’ mobiles

This new function allows you to email values for intraocular pressure and corneal thickness as well as impressive videos to your patients. Videos include a feature for reminding patients of upcoming follow-up exams. This way you can convince them – in particular the young ones – of the necessity for glaucoma screenings and regular follow-up exams. The high-end diagnostics provided by the Corvis® ST will put the focus on your performance and high-tech equipment.

Measurement and Display Options

  • IOP measurement
  • Measurement of the corneal thickness
  • Scheimpflug images of the 1st and 2nd applanation of the cornea
  • Slow-motion video of the corneal deformation as a result of the air pulse
  • Non-contact tonometer in combination with an ultra-high-speed camera for visualization of the deformation of the cornea in reaction to an air pulse (4 330 frames / sec.)

The tool of tomorrow today

The Corvis® ST is now available in various software versions. You can start making economic use of it now. You will receive a combined Tonometer and Pachymeter complete with video function and a new email function designed for sending videos to patients´ mobiles. You can upgrade later on, adding information on biomechanical properties of the cornea from the Dynamic Corneal Response Display.

Applications Corvis® ST
IOD/Pachymetry ✓
Pachymetric Progression ✓
High-speed video of the cornea ✓
Email function for sending high-speed video ✓
DCR-Software incl. CBI and TBI optional
Biomechanical Glaucoma Factor (BGF) optional

Biomechanical Properties

Why are biomechanical properties so important?

Applications

The role of the Corvis® ST in glaucoma diagnostics

The Corvis® ST measures IOP, corneal thickness and the deformation response of the cornea. Based on these data it has the potential to determine an IOP value that is uninfluenced by corneal biomechanical properties.

Screening for corneal ectasia

Corneal ectasia leads to changes in the viscoelastic properties of the cornea. These changes can be analyzed based on deviations in deformation response parameters relative to normal eyes.

Visualizing the effect of corneal crosslinking

Changes in deformation characteristics due to corneal crosslinking can also be measured with the Corvis® ST. The Corvis® ST has the potential to quantify the effect of crosslinking on the biomechanical properties of the cornea.

Videos

OCULUS Corvis® ST

The proof is in the picture!

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FAQ

The Corvis® ST is the first device in clinical practice that provides a parameter for corneal stiffness.
Corneal stiffness is a term to describe the overall rigidity of the cornea – it is a measure of the resistance against elastic deformation as a response to the applied force. Bending stiffness can be calculated based on the applied force over displacement along the same direction as the force is transferred.
The stiffness parameter introduced by Cynthia Roberts has been proven to be important for both detection of keratoconus and for prediction of glaucoma progression.

The biomechanical corrected IOP (bIOP) takes corneal thickness, age and the biomechanical properties of the cornea into consideration. This enables an accurate IOP estimation even in case of altered biomechanical properties.

The equation was derived based on so-called finite element simulations. In numerical simulations the influence of corneal stiffness, corneal thickness, curvature and the biomechanical properties on IOP measurements was analysed systematically.
Based on these results an equation was developed that compensates for these influencing factors. Experimental studies with cadaver eyes and clinical studies have proven the accuracy of the bIOP.

Traditional non-contact tonometers are tear film dependent as the measurement procedure is based on reflection technology. Corvis® ST incorporates Scheimpflug photography during its measurement procedure and is therefore not dependent on tear film, fixation or decentred apex. Even highly irregular corneas can have accurate measurements obtained.

The Corvis® ST software contains a database with normative values for the DCR parameters for different IOPs. A bIOP value is calculated for each patient after a Corvis® ST measurement. As a result, the patient’s measured DCR parameters can be compared to the DCR parameters in the database linked to the same bIOP.

The CBI was developed in order to detect early biomechanical changes in case of an early ectasia. It is based on a logistic regression formula including different Dynamic Corneal Response (DCR) parameters, the Stiffness Parameter and the corneal thickness profile of the horizontal sectional plane. In a large multicentre study the high accuracy of this index to distinguish normal eyes from eyes with keratoconus was proven. In this study including more than 600 eyes the accuracy was higher than 98 percent. Moreover, the clinical use of this index in case of subclinical or forme fruste keratoconus was proven in another publication. Many of these cases could be detected by the CBI, even though no topographic or tomographic abnormalities could be observed. These case examples support the hypothesis that biomechanical changes occur before morphological changes are present.

Prof. Renato Ambrósio from Brazil developed an index that combines tomographic and biomechanical parameters in order to reach maximal accuracy. Based on a so-called random forest algorithm – a modern machine learning approach – an overall risk score is provided to evaluate ectasia susceptibility.

A random forest algorithm consists of 500 different uncorrelated decision trees – each using tomographic and biomechanical parameters. Each tree makes a classification being either normal or ectasia based on the input variables. The TBI finally represents the percentage, how many trees the cornea classified as normal and how many as abnormal.

In a validation study this index had the highest accuracy for the detection of subclinical keratoconus compared to all other tested methods including corneal topography and tomography. Current cross-validation from Brazil, India, Iran, Hong Kong and Germany indicate similar results.

In combination with the Corvis® ST the TBI can be calculated based on any device of the Pentacam family: Either a standard Pentacam®, a Pentacam® HR or the Pentacam® AXL. The only requirement is a software license for the software Belin/Ambrósio Enhanced Ectasia Display.

What is a Random Forest?
A random forest approach is a modern, state of the art machine learning approach. A random forest consists of 500 different uncorrelated decision trees.

A decision tree is a hierarchical tree-like model of decisions. The decision tree has different splitting paths which are followed according to certain decision rules. At the end of the tree are the leaves which represent the final classification of the decision tree. One problem of using a single decision tree for classification is that the prediction is either 100 % correct or 100 % incorrect.

Therefore, a random forest uses 500 different decision trees. During training each tree has grown in a randomized way and uses different parameters for classification. For the final classification each tree gives a classification and the final index provides the percentage of trees with a certain classification.

Video: Watch Prof Ambrósio’s explanation of Random Forest here (Englisch)

Technical Data

Tonometer

Measurement range 6 – 60 mmHg
Measurement distance 11 mm (0.4 in)
Inner fixation light Rote LED
3D auto tracking & auto release

Scheimpflug camera

Frame rate 4 330 images per sec
Measurement range 8.5 mm (0.3 in) horizontal coverage
Pachymeter measurement range 300 – 1 200 μm
Measuring points 576 per image (576 x 200 pixel)
Source of light Blue LED (470 nm UV free)

Technical specifications

Dimensions (W x D x H) 266 x 538 x 495 – 525 mm
(10.5 x 21.2 x 19.5 – 20.7 in)
Weight 14 kg (30.8 lbs)
Max. power consumption 26 W
Voltage 100 – 240 V AC
Voltage 50 – 60 Hz
Recommended computer specifications Intel® Core™ i5, 500 GB SSD, 8 GB RAM, Windows® 11, Intel® HD Graphics

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Tel. +49 641 2005-800