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. 2021 Nov 16;8(1):44.
doi: 10.1186/s40662-021-00266-y.

Comparisons of corneal biomechanical and tomographic parameters among thin normal cornea, forme fruste keratoconus, and mild keratoconus

Lei Tian #  1   2 , Di Zhang #  3   4 , Lili Guo  1 , Xiao Qin  3   4 , Hui Zhang  3   4 , Haixia Zhang  3   4 , Ying Jie  5 , Lin Li  6   7
Affiliations

Comparisons of corneal biomechanical and tomographic parameters among thin normal cornea, forme fruste keratoconus, and mild keratoconus

Lei Tian et al. Eye Vis (Lond). .

Abstract

Background: To compare the dynamic corneal response (DCR) and tomographic parameters of thin normal cornea (TNC) with thinnest corneal thickness (TCT) (≤ 500 µm), forme fruste keratoconus (FFKC) and mild keratoconus (MKC) had their central corneal thickness (CCT) matched by Scheimpflug imaging (Pentacam) and corneal visualization Scheimpflug technology (Corvis ST).

Methods: CCT were matched in 50 eyes with FFKC, 50 eyes with MKC, and 53 TNC eyes with TCT ≤ 500 µm. The differences in DCR and tomographic parameters among the three groups were compared. The receiver operating characteristic (ROC) curve was used to analyze the diagnostic significance of these parameters. Back propagation (BP) neural network was used to establish the keratoconus diagnosis model.

Results: Fifty CCT-matched FFKC eyes, 50 MKC eyes and 50 TNC eyes were included. The age and biomechanically corrected intraocular pressure (bIOP) did not differ significantly among the three groups (all P > 0.05). The index of height asymmetry (IHA) and height decentration (IHD) differed significantly among the three groups (all P < 0.05). IHD also had sufficient strength (area under the ROC curves (AUC) > 0.80) to differentiate FFKC and MKC from TNC eyes. Partial DCR parameters showed significant differences between the MKC and TNC groups, and the deflection amplitude of the first applanation (A1DA) showed a good potential to differentiate (AUC > 0.70) FFKC and MKC from TNC eyes. Diagnosis model by BP neural network showed an accurate diagnostic efficiency of about 91%.

Conclusions: The majority of the tomographic and DCR parameters differed among the three groups. The IHD and partial DCR parameters assessed by Corvis ST distinguished FFKC and MKC from TNC when controlled for CCT.

Keywords: Corneal biomechanical parameters; Forme fruste keratoconus; Mild keratoconus; Thin normal cornea.

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Conflict of interest statement

The authors declare that there is no conflict of interests regarding the publication of this study.

Figures

Fig. 1
Fig. 1
Corvis ST parameters measured, first applanation (a), highest concavity (b), second applanation (c). A1DA, corneal deflection amplitude during the first applanation; A1L, length at the first applanation; A1T, time from starting until the first applanation; HCDA, corneal deflection amplitude at the moment of the highest corneal concavity; PD, peak distance at the highest concavity; HCR, central concave curvature at highest concavity; HCDL, highest concavity deflection length; HCT, time from the measurement beginning to the moment of reaching the highest concavity; A2DA, corneal deflection amplitude during the second applanation; A2L, length at the second applanation; A2T, time from starting until the second applanation
Fig. 2
Fig. 2
Differences between the three groups with respect to IHA (a) and IHD (b). *, # and &represent statistically significant differences between TNC and FFKC, TNC and MKC, and FFKC and MKC, respectively. IHA, index of height asymmetry; IHD, index of height decentration; TNC, thin normal cornea; FFKC, forme fruste keratoconus; MKC, mild keratoconus
Fig. 3
Fig. 3
The receiver operating characteristic curves for MKC vs. FFKC for Pentacam (a) and Corvis ST (b) parameters. FFKC, forme fruste keratoconus; MKC, mild keratoconus
Fig. 4
Fig. 4
Results of keratoconus (KC) diagnosis with the keratoconus diagnosis model. <  − 0.5: MKC group; [− 0.5, 0.5): FFKC group; ≥ 0.5: TNC group. TNC, thin normal cornea; FFKC, forme fruste keratoconus; MKC, mild keratoconus
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