Application of Pentacam in the early diagnosis of keratoconus

Abstract

Objective To investigate the change in morphologic parameters using the Pentacam to discriminate between clinical keratoconus eyes,subclinical keratoconus eyes and normal eyes for early diagnosis.Methods This was a case control study.Adopting the Rabinowitz diagnosis standards,we divided 35 patients with keratoconus into 2 subgroups:16 patients (16 eyes) with clinical keratoconus and 19 patients (19 eyes) with subclinical keratoconus.Twenty-nine patients (29 eyes) with myopic astigmatism were used as a control group.The following morphologic parameters of the anterior corneal surface provided by Pentacam in the clinical keratoconus group,subclinical keratoconus group and control group were recorded:index of surface variance (ISV),index of vertical asymmetry (IVA),keratoconus index (KI),central keratoconus index (CKI),index of highest asymmetry (IHA),index of highest decentration (IHD),minimum sagittal curvature (Rmin) and aberration coefficient (ABR).An analysis of variance,Dunnett-t test and receiver operating characteristic (ROC) curves were used for analysis and partial least squares (PLS) was used to construct models with corneal morphologic parameters of the anterior corneal surface for early diagnosis.Results There were significant differences between the clinical keratoconus group,subclinical keratoconus group and control group.The values of the area under the curve (AUC) were all close to 1,and the diagnosis accuracy was high.The optimum cutoff points of the ISV for clinical keratoconus and subclinical keratoconus were 39 and 22.4,Rmin was 6.765 and 7.11,and KI was 1.085 and 1.045.The PLS model of clinical keratoconus was Yhat=8.231+0.006×ISV+ 0.843×IVA+ 0.869×KI-3.186×CKI-0.010×IHA+ 0.679×IHD-0.649×Rmin-0.057×ABR,and the PLS model of subclinical keratoconus was Yhat=7.861-0.563×Rmin+ 0.018× ISV+ 0.390×IVA-3.281×KI+ 0.571×CKI-0.010×IHA+ 0.727 ×IHD-0.009×ABR.Conclusion Pentacam is important in the early diagnosis of clinical keratoconus eyes and subclinical keratoconus. Key words: Keratoconus; Pentacam; Anterior coneal surface; Morphological parameter