Corneal Biomechanical Assessment with Ultra-High-Speed Scheimpflug Imaging During Non-Contact Tonometry: A Prospective Review

Figures & data

Table 1 Ultra-High-Speed Scheimpflug Camera-Based Corneal Biomechanical Parameters with Explanation

Parameters	Abbreviations	Explanation
Corvis-derived non-contact tonometry IOP [mmHg]	cIOP	Corvis-derived intraocular pressure
Corvis-derived central corneal thickness [µm]	cCCT	Corvis-derivated central corneal thickness
1st Generation Parameters	Abbreviations	Explanation
Deformation Amp. Max [mm]	MaxDefoA	Corneal deformation amplitude during MaxDT, as the sum of corneal deflection amplitude and MaxWEM
A1 Time [ms]	A1T	Time from the measurement beginning to the first applanation moment
A1 Velocity [m/s]	A1V	Velocity of the corneal apex during the first applanation
A2 Time [ms]	A2T	Time from the measurement beginning to the second applanation moment
A2 Velocity [m/s]	A2V	Velocity of the corneal apex during the second applanation
HC Time [ms]	HCT	Time from the measurement beginning to the moment of reaching the highest concavity (HC)
Peak Dist. [mm]	HCPD	Distance between the corneal peaks at the HC
Radius [mm]	HCR	Radius of corneal curvature during the HC
A1 Deformation Amp. [mm]	A1DefoA	Corneal deformation amplitude during A1, as the sum of corneal deflection amplitude and MaxWEM
HC Deformation Amp. [mm]	HCDefoA	Corneal deformation amplitude during HC, as the sum of corneal deflection amplitude and MaxWEM
A2 Deformation Amp. [mm]	A2DefoA	Corneal deformation amplitude during A2, as the sum of corneal deflection amplitude and MaxWEM
A1 Deflection Length [mm]	A1DL	Horizontal length of the flattened cornea at the A1
HC Deflection Length [mm]	HCDL	Horizontal length of the flattened cornea at the HC
A2 Deflection Length [mm]	A2DL	Horizontal length of the flattened cornea at the A2
A1 Deflection Amp. [mm]	A1DA	Corneal deflection amplitude during A1, determined as the displacement of the corneal apex in relation to the initial state without the MaxWEM quantification
HC Deflection Amp. [mm]	HCDA	Corneal deflection amplitude during HC, determined as the displacement of the corneal apex in relation to the initial state without the MaxWEM quantification
A2 Deflection Amp. [mm]	A2DA	Corneal deflection amplitude during A2, determined as the displacement of the corneal apex in relation to the initial state without the MaxWEM quantification
Deflection Amp. Max [mm]	MaxDA	Corneal deformation amplitude during MaxDT, as the sum of corneal deflection amplitude and MaxWEM
Deflection Amp. Max [ms]	MaxDT	Moment of the maximum deformation, during the oscillatory phase near HC
Whole Eye Movement Max [mm]	MaxWEM	Amplitude of the Maximum whole eye movement
Whole Eye Movement Max [ms]	MaxWEMT	Time at which occurs the amplitude of the Maximum whole eye movement (near A2)
A1 Deflection Area [mm2]	A1DArea	Deflection area in A1
HC Deflection Area [mm2]	HCDArea	Deflection area in HC
A2 Deflection Area [mm2]	A2DArea	Deflection area in A2
A1 dArc Length [mm]	A1dArcL	Delta arc length of corneal surface in A1
HC dArc Length [mm]	HCdArcL	Delta arc length of corneal surface in HC
A2 dArc Length [mm]	A2dArcL	Delta arc length of corneal surface in A2
dArcLengthMax [mm]	MaxdArcL	Delta arc length of corneal surface in MaxDT
2nd Generation Parameters	Abbreviations	Explanation
Max InverseRadius [mm^-1]	MIR	1/HCR
DA Ratio Max (2mm)	DARM2	Ápex MaxDA/MaxDA at 2mm from the ápex
PachySlope [µm]	PqS	Peripheric (8mm horizontal) pachymetry/Ápex pachymetry
DA Ratio Max (1mm)	DARM1	Ápex MaxDA/MaxDA at 1mm from the ápex
Ambrosio Relational Thickness (horizontal 8mm)	ARTh	Ambrosio Relational Thickness in the horizontal 8mm cornea of the image
Biomechanically-corrected IOP	bIOP	IOP adjusted for biomechanical parameters
Integrated Radius [mm^-1]	IR	Area under the curve of the 1/HCR function
Stiffness parameter in A1	SP-A1	Air puff pressure - bIOP/A1DA
Stress Strain Index	SS-I	Finite element modeling algorithm for the estimation of the non-linear in vivo biomechanical behaviour in corneal with normal topography
Corvis biomechanical index	CBI	Exponential function score made through a logistic regression analysis of 6 parameters (SP-A1, DARM1, DARM2, ARTh, A1V and MaxDefoA) and adjusted for IOP and CCT to describe ectasia risk
Tomographic and biomechanical Index	TBI	Generated by the random Forest method with leave-one-out cross-validation, including tomographic and biomechanical parameters, to detect ectasia susceptibility

Figure 1 Example of a print-out from the Corvis ST^® describing the corneal, shape within different timepoints and several biomechanical parameters.

Notes : Copyright ©2021. Reproduced from Baptista PM, Marta AA, Marques JH, Abreu AC, Monteiro S, Menéres P, Pinto MDC. The Role of Corneal Biomechanics in the Assessment of Ectasia Susceptibility Before Laser Vision Correction. Clin Ophthalmol. 2021;15:745-758.¹⁴⁶

Baptista PM, Marta AA, Marques JH, Abreu AC, Monteiro S, Menéres P, Pinto MDC The Role of Corneal Biomechanics in the Assessment of Ectasia Susceptibility Before Laser Vision Correction. Clin Ophthalmol. 2021;15:745–758. https://doi.org/10.2147/OPTH.S296744

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