Evaluation of the Relationship Between the Changes in the Corneal Biomechanical Properties and Changes in the Anterior Segment OCT Parameters Following Customized Corneal Cross-Linking

Figures & data

Table 1 Demographic Information of the Entire Patient Cohort

Parameter
Patients (n)	44
Age (y)	22.8 ± 6.4
Sex, men/women	33/11
IOP (mmHg)	9.82 ± 2.27
bIOP (mmHg)	14.53 ± 1.60
UDVA (logMAR)	0.73 ± 0.52
CDVA (logMAR)	0.12 ± 0.26
Scheimpflug-based tonometer
Integrated radius (1/mm)	12.19 ± 1.95
Max inverse radius (1/mm)	0.24 ± 0.04
DA ratio max (2 mm)	5.53 ± 0.81
SP-A1	71.09 ± 19.14
SSI	0.74 ± 0.16
Anterior segment OCT
Average keratometry (D)	47.87 ± 3.61
Steep keratometry (D)	49.61 ± 4.01
Corneal astigmatism (D)	3.48 ± 1.84
Kmax (D)	55.44 ± 6.22
Thinnest corneal thickness (µm)	450.43 ± 41.74

Abbreviations: IOP, intraocular pressure; bIOP, biomechanically corrected intraocular pressure; UDVA, uncorrected distance visual acuity; CDVA, corrected distance visual acuity; Integrated radius, integrated area under the curve of the inverse concave radius; Max inverse radius, maximum inverse radius; DA ratio max, deformation amplitude ratio max 2 mm; SP-A1, stiffness parameter at applanation 1; SSI, stress-strain index; D, diopter; Kmax, maximum keratometry; OCT, optical coherence tomography.

Table 2 Comparison of the Preoperative and Postoperative CXL Intraocular Pressure Values and Uncorrected Distance Visual Acuity and Corrected Distance Visual Acuity

Parameter	Preoperative CXL	Postoperative CXL	p
IOP (mmHg)	9.82 ± 2.27	11.47 ± 3.00	<0.0001
bIOP (mmHg)	14.53 ± 1.60	16.46 ± 1.90	<0.0001
UDVA (logMAR)	0.73 ± 0.52	0.58 ± 0.49	0.0004
CDVA (logMAR)	0.12 ± 0.26	0.05 ± 0.21	0.095

Abbreviations: IOP, intraocular pressure; bIOP, biomechanically corrected intraocular pressure; UDVA, uncorrected distance visual acuity; CDVA, corrected distance visual acuity; CXL, corneal cross-linking.

Table 3 Comparison of the Preoperative and Postoperative CXL SBT Parameters

Parameter	Preoperative CXL	Postoperative CXL	p
Integrated radius (1/mm)	12.19 ± 1.95	11.26 ± 1.89	<0.0001
Max inverse radius (1/mm)	0.24 ± 0.04	0.23 ± 0.04	0.0053
DA ratio max (2 mm)	5.53 ± 0.81	5.29 ± 0.71	0.0048
SP-A1	71.09 ± 19.14	75.01 ± 17.63	0.0679
SSI	0.74 ± 0.16	0.84 ± 0.20	<0.0001

Abbreviations: Integrated radius, integrated area under the curve of the inverse concave radius; Max inverse radius, maximum inverse radius; DA ratio max, deformation amplitude ratio max 2 mm; SP-A1, stiffness parameter at applanation 1; SSI, stress-strain index; CXL, corneal cross-linking; SBT, Scheimpflug-based tonometer.

Table 4 Comparison of the Preoperative and Postoperative CXL AS-OCT Parameters

Parameter	Preoperative CXL	Postoperative CXL	p
Average keratometry (D)	47.87 ± 3.61	47.56 ± 3.29	0.0104
Steep keratometry (D)	49.61 ± 4.01	49.25 ± 3.59	0.0115
Corneal astigmatism (D)	3.48 ± 1.84	3.38 ± 1.68	0.4921
Kmax (D)	55.44 ± 6.22	54.68 ± 5.56	0.0061
Thinnest corneal thickness (µm)	450.43 ± 41.74	444.00 ± 39.35	< 0.0001

Abbreviations: D, diopter; Kmax, maximum keratometry; AS-OCT, anterior segment optical coherence tomography; CXL, corneal cross-linking.

Table 5 Multiple Regression Analysis Investigating Factors Affecting the Changes in the Preoperative and Postoperative CXL SBT Parameters

Dependent Variable	Explanatory Variables	Partial Regression Coefficient	Standardized Partial Regression Coefficient	VIF	Coefficient of Determination (R^2)
ΔIntegrated radius (1/mm)	None
ΔMax inverse radius (1/mm)	None
ΔDA Ratio Max (2 mm)	Age	0.032	0.407	1.040	0.327
	Δaverage K (D)	0.247	0.348	1.044
	Δthinnest (µm)	−0.015	−0.292	1.004
ΔSP-A1	ΔIOP (mmHg)	1.794	0.338	1.000	0.115
ΔSSI	ΔIOP (mmHg)	0.022	0.363	1.000	0.132

Abbreviations: VIF, variance inflation factor; Integrated radius, integrated area under the curve of the inverse concave radius; Max inverse radius, maximum inverse radius; DA ratio max, deformation amplitude ratio max 2 mm; SP-A1, stiffness parameter at applanation 1; SSI, stress-strain index; D, diopter; average K, Average keratometry; thinnest, Thinnest corneal thickness; IOP, intraocular pressure; CXL, corneal cross-linking; SBT, Scheimpflug-based tonometer.

Figure 1 Correlation between Δcorneal biomechanical parameters and other parameters. A moderate positive correlation was found between the Δdeformation amplitude (DA) ratio max (2 mm) and age (A) (R=0.305, p=0.044). No significant correlation was found between the ΔDA Ratio Max (2 mm) and Δaverage K (B) (R=0.228, p=0.137). No significant correlation was found between the ΔDA Ratio Max (2 mm) and Δthinnest (C) (R=−0.265, p=0.083). A moderate positive correlation was found between the Δstiffness parameter at applanation 1 (SP-A1) and Δintraocular pressure (IOP) (D) (R=0.332, p=0.028). A moderate positive correlation was found between the Δstress-strain index (SSI) and ΔIOP (E) (R=0.308, p=0.042).

Figure 2 Correlation between each anterior segment optical coherence tomography (AS-OCT) parameter change and Δintegrated radius. No significant correlation was found between the change in each AS-OCT parameter and Δintegrated radius. ((A) Δaverage K, R=0.071, p=0.648) ((B) Δsteep K, R=0.147, p=0.342) ((C) Δcylinder, R=0.117, p=0.449) ((D) Δmaximum keratometry [Kmax], R=0.180, p=0.242) ((E) Δthinnest, R=−0.138, p=0.370).

Figure 3 Correlation between each anterior segment optical coherence tomography (AS-OCT) parameter change and Δ maximum (Max) inverse radius. No significant correlation was found between the change in each AS-OCT parameter and ΔMax inverse radius. ((A) Δaverage K, R=0.027, p=0.863) ((B) Δsteep K, R=0.029, p=0.854) ((C) Δcylinder, R=0.017, p=0.912) ((D) Δ maximum keratometry [Kmax], R=0.025, p=0.872) ((E) Δthinnest, R=−0.147, p=0.340).

Figure 4 Correlation between each anterior segment optical coherence tomography (AS-OCT) parameter change and ΔDA ratio max (2 mm). No significant correlation was found between the change in each AS-OCT parameter and Δ deformation amplitude (DA) ratio max (2 mm). ((A) Δaverage K, R=0.228, p=0.137) ((B) Δsteep K, R=0.196, p=0.201) ((C) Δcylinder, R=0.075, p=0.628) ((D) Δ maximum keratometry [Kmax], R=0.216, p=0.159) ((E) Δthinnest, R=−0.265, p=0.083).

Figure 5 Correlation between each anterior segment optical coherence tomography (AS-OCT) parameter change and Δ stiffness parameter at applanation 1 (SP-A1). No significant correlation was found between the change in each AS-OCT parameter and ΔSP-A1. ((A) Δaverage K, R=−0.030, p=0.848) ((B) Δsteep K, R=−0.038, p=0.805) ((C) Δcylinder, R=−0.018, p=0.905) ((D) ΔKmax, R=−0.028, p=0.858) ((E) Δthinnest, R=0.47, p=0.762).

Figure 6 Correlation between each anterior segment optical coherence tomography (AS-OCT) parameter change and Δ stress-strain index (SSI). No significant correlation was found between the change in each AS-OCT parameter and ΔSSI. ((A) Δaverage K, R=−0.036, p=0.818) ((B) Δsteep K, R=−0.022, p=0.888) ((C) Δcylinder, R=−0.017, p=0.913) ((D) Δ maximum keratometry [Kmax], R=−0.111, p=0.474) ((E) Δthinnest, R=0.38, p=0.806).