Corneal biomechanics and glaucoma beyond the bidirectional impact of intraocular pressure and corneal deformation response

Brazuna, Rodrigo; Salomão, Marcella; Esporcatte, Bruno; Macedo, Marcelo; Esporcatte, Louise; Colombini, Giovanni Nicola Umberto Italiano; Ambrósio Júnior, Renato

doi:10.37039/1982.8551.20220036

Rodrigo Brazuna

Department of Ophthalmology, Universidade Federal do Estado do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.

http://orcid.org/0000-0002-7480-5659

Marcella Salomão

Rio de Janeiro Corneal Tomography and Biomechanics Study Group, Rio de Janeiro, RJ, Brazil.

http://orcid.org/0000-0001-8330-6432

Bruno Esporcatte

Department of Ophthalmology, Universidade Federal de São Paulo, São Paulo, SP, Brazil.

http://orcid.org/0000-0002-4509-7075

Marcelo Macedo

Department of Ophthalmology, Universidade de São Paulo, São Paulo, SP, Brazil.

http://orcid.org/0000-0002-9262-4819

Louise Esporcatte

Rio de Janeiro Corneal Tomography and Biomechanics Study Group, Rio de Janeiro, RJ, Brazil.

http://orcid.org/0000-0002-2353-9442

Giovanni Nicola Umberto Italiano Colombini

Department of Ophthalmology, Universidade Federal do Estado do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.

http://orcid.org/0000-0003-0269-2883

Renato Ambrósio JúniorCorresponding author: Renato Ambrósio Júnior, Rua Conde de Bonfim 211/712 Zip code: 20520-050 – Rio de Janeiro, RJ, Brazil E-mail: dr.renatoambrosio@gmail.com

Department of Ophthalmology, Universidade Federal do Estado do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.

http://orcid.org/0000-0001-6919-4606

Corresponding author: Renato Ambrósio Júnior, Rua Conde de Bonfim 211/712 Zip code: 20520-050 – Rio de Janeiro, RJ, Brazil E-mail: dr.renatoambrosio@gmail.com

Conflict of interest the authors declare no conflict of interest.

Figures (5)
Tables (1)

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Figure 1
Ocular Response Analyzer® measurements showing the air pulse deforming the cornea (ingoing phase) and registering P1 (first applanation moment), the Gaussian configuration is formed when the air pulse gradually shuts off; then, with the continuity of the air pulse, the cornea assumes a concavity configuration. In the outgoing phase (air pressure decreases), the cornea passes through a second applanation, when the pressure of the air pulse (P2) is again registered. The pressure-derived parameters generated are corneal hysteresis and corneal resistance factor. This is a composite made by the authors of classic pictures available in the public domain.

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Figure 2
Standard Corvis® ST parameters. The figure shows the deformation amplitude, applanation lengths, corneal velocities recorded during ingoing and outgoing phases and the radius of curvature at the highest concavity (curvature radius highest concavity), thereby corneal thickness and intraocular pressure are calculated and registered.

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Figure 3
The Vinciguerra Screening Report. This display provides correlations of normality values and a biomechanically adjusted intraocular pressure. It uses a calibration factor to calculate the intraocular pressure value based on the pressure at the time of the first applanation. It empowers the calculation of the Ambrósio Relational Thickness over the horizontal meridian and the Corvis® Biomechanical Index.

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Figure 4
The biomechanical glaucoma factor. This index shows the likelihood for specific patient being more comparable to biomechanical behavior of healthy patients or normal-tension glaucoma.

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Figure 5
The Stress-Strain Index. This index indicates the cornea’s stiffness and describes the cornea’s intrinsic elastic properties less dependent on corneal thickness or intraocular pressure. It is calculated by element finite and describes the position of the stress-strain curve, and the cornea is considered softer when curves are shifted to the right or the index value is smaller than one. Furthermore, it is considered stiffer when the curves are shifted to the left and the index is bigger than one.

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Table 1
Corneal deformation parameters provided by the Corvis® ST

Corvis® ST – parameters
First applanation	The first applanation of the cornea during the air puff (in milliseconds). The length of the applanation at this moment appears in parenthesis (in millimeters)
Highest concavity	The instant that the cornea assumes its maximum concavity during the air puff (in milliseconds). The length of the distance between the two peaks of the cornea at this moment appears in parenthesis (in millimeters)
Second applanation	The second applanation of the cornea during the air puff (in milliseconds). The length of the applanation at this moment appears in parenthesis (in millimeters)
Maximum deformation	The amount (in millimeters) of the maximum cornea deformation during the air puff
Wing distance	The length of the distance between the two peaks of the cornea at this instant (in millimeters)
Maximum velocity (in)	Maximum velocity during the ingoing phase (in meters per second)
Maximum velocity	The maximum velocity during the outgoing phase (in meters per second)
Curvature radius normal	The cornea in its natural state radius of curvature (in millimeters)
Curvature radius highest concavity	The cornea radius of curvature at the time of maximum concavity during the air puff (in millimeters)
Cornea thickness	Measurement of the corneal thickness (in millimeters)
IOP	Measurement of the intraocular pressure (in mmHg)
bIOP	Biomechanically-corrected IOP
Deformation amplitude ratio maximum 2mm	Ratio between the deformation amplitude at the apex and the average deformation amplitude measured at 2mm from the left
Ambrósio’s relational thickness to the horizontal profile	Describes thickness profile in the temporal-nasal direction and is defined as the thinnest corneal thickness to pachymetric progression
Stiffness parameter at A1	Describes corneal stiffness as defined by the resultant pressure divided by deflection amplitude at A1
Stiffness parameter- highest concavity	Corneal stiffness at the highest concavity point
Tomographic biomechanical index	Index that combined tomographic and biomechanical data to keratoconus detection
Biomechanical glaucoma factor	Independent risk indicator for normal tension glaucoma
Stress-strain index	Index that indicates the position of the stress-strain curves. Less dependent on corneal thickness and IOP
Corvis® biomechanical index	Overall biomechanical index for keratoconus detection

[1] Corresponding author: Renato Ambrósio Júnior, Rua Conde de Bonfim 211/712 Zip code: 20520-050 – Rio de Janeiro, RJ, Brazil E-mail: dr.renatoambrosio@gmail.com

Brasil

Brasil

Corneal biomechanics and glaucoma beyond the bidirectional impact of intraocular pressure and corneal deformation response

Biomecânica corneana e glaucoma além do impacto bididirecional da pressão intraocular e da resposta da deformação corneana

ABSTRACT