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Journal of Peking University(Health Sciences) ›› 2019, Vol. 51 ›› Issue (5): 881-886. doi: 10.19723/j.issn.1671-167X.2019.05.015

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Examination and discriminant analysis of corneal biomechanics with CorVis ST in keratoconus and subclinical keratoconus

Yuan WU1,Xiao-li LI2,Song-lin YANG1,Xiao-ming YAN1,Hai-li LI1,△()   

  1. 1. Department of Ophthalmology, Peking University First Hospital, Beijing 100034, China
    2. Department of Ophthalmology, Tianjin Eye Hospital, Tianjin 300020, China
  • Received:2017-09-06 Online:2019-10-18 Published:2019-10-24
  • Contact: Hai-li LI E-mail:lihaili2013@sina.cn
  • Supported by:
    Supported by the National Natural Science Foundation of China(11372011)

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Abstract:

Objective: To compare the corneal biomechanical properties among keratoconus, subclinical keratoconus and normal corneas by using CorVis ST, and to estimate the effect of these biomechanical indices in discriminating keratoconus and subclinical keratoconus from normal. Methods: A total of 76 eyes of 67 subjects were enrolled and divided into three groups. Keratoconus group included 24 eyes from 17 patients, subclinical keratoconus group included 12 eyes from 12 patients and normal group included 40 normal eyes from 40 subjects.All the eyes were assessed with CorVis ST and ten biomechanical para-meters, intraocular pressure (IOP) and central corneal thickness (CCT) were obtained from this machine. The discrimination of biomechanical characteristic of the three groups based on the all indices was reflected by discriminant analysis and the Fisher discriminant function was established. Results: The values of corneal biomechanics of keratoconus, subclinical keratoconus, normal eyes were increased in sequence, except for three indices: the second applamation time (A2T), time taken to reach highest concavity (HCT) and maximum corneal velocity during the first applanation (Vin). Three sets of data were among a statistically significant difference (P<0.05). There were statistically significant differences (P<0.05) between any two groups by comparing with such two indices: radius value of central concave curvature at highest concavity (HCR) and CCT. The grades of the three groups were obvious, evaluated by the discriminant function. The accuracy of reevaluation was 85% by validation method. The biggest contribution of indices in discriminant function was given by such four indices in sequence: CCT, HCR, maximum deformation amplitude of highest concavity (HCDA) and maximum corneal velocity during the second applanation (Vout). Conclusion: The corneal biomechanical properties of keratoconus and subclinical keratoconus were decreased compared with normal eyes. The biomechanical parameters based on CorVis ST showed a good performance for discriminating among keratoconus, subclinical keratoconus and normal corneas.

Key words: Keratoconus, Biomechanics, Discrimination analysis

CLC Number: 

  • R772.2

Figure 1

Deformation stages of cornea A, initial stage of cornea; B, stage offirst applanation; C, stage of highest concavity; D, stage of second applanation."

Figure 2

Control surface and all parameters of CorVis ST"

Table 1

Corneal biomechanical parameters comparison of three groups"

Parameters Keratoconus (n=24) Subclinical keratoconus (n=12) Control (n=40) Statistics P
A1T/ms, x?±s 6.95±0.22 7.15±0.27 7.37±0.38 F=5.816 <0.001
A2T/ms, M (P25, P75) 21.98 (16.89, 22.82) 21.62 (16.67, 22.53) 21.81 (16.42, 22.64) χ2=4.687 0.176
HCT/ms, M (P25, P75) 16.85 (15.29, 22.33) 16.59 (13.78, 17.69) 16.89 (14.84, 22.94) χ2=3.155 0.061
A1L/mm, M (P25, P75) 1.65 (1.13, 1.79) 1.76 (1.33, 1.86) 1.77 (1.28, 1.89) χ2=24.587 <0.001
Vin/(m/s), M (P25, P75) 0.16 (0.14, 0.23) 0.16 (0.13, 0.17) 0.15 (0.07, 0.19) χ2=3.061 0.019
A2L/mm, x?±s 1.21±0.34 1.57±0.35 1.64±0.31 F=-3.888 0.040
Vout/(m/s), x?±s 0.53±0.19 0.34±0.08 0.35±0.09 F=4.326 <0.001
PD/mm, M (P25, P75) 4.95 (2.46, 6.31) 4.84 (2.46, 5.36) 4.52 (1.92, 6.27) χ2=10.050 <0.001
HCR/mm, x?±s 4.37±1.17 5.64±1.89 6.75±1.36 F=7.136 <0.001*
HCDA/mm, x?±s 1.33±0.16 1.12±0.09 1.08±0.14 F=-6.501 <0.001
IOP/mmHg, x?±s 9.43±2.16 11.63±3.03 13.8±4.02 F=5.572 <0.001
CCT/μm, x?±s 446.2±56.3 496.3±35.37 534.3±36.3 F=6.855 <0.001*

Figure 3

Score plot of all the corneal biomechanical parameters in the 2 discrimination functions"

Table 2

The results of return analysis"

Verification method Groups Keratoconus, n(%) Subclinical
keratoconus, n(%)		 Control, n(%) Total Correct
judgement
Auto-verification Keratoconus 18 (75) 6 (25) 0 24 75.0%
Subclinical keratoconus 0 11 (91.7) 1 (8.3) 12 91.7%
Control 2 (5) 2 (5) 36 (90) 40 90.0%
Cross-vertification Keratoconus 16 (66.7) 6 (25) 2 (8.3) 24 66.7%
Subclinical keratoconus 3 (25) 6 (50) 3 (25) 12 50.0%
Control 3 (7.5) 4 (10) 33 (82.5) 40 82.5%
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