| Objective: To investigate the diagnostic value of corneal densitometry and corneal topography for keratoconus by comparing the changes of corneal densitometry in normal people and keratoconus.Methods: Retrospective research.A total of 89 cases(89 eyes)in the normal control group and 68 cases(130 eyes)in the keratoconus group were included.Pentacam analysis system was used to measure the corneal densitometry value of anterior layer(up to 120μm),posterior layer(posterior 60μm),middle layer(between the anterior and posterior)and the total layer as well as the diameters of 0～2mm,2～6mm,6～10mm,and 0～12mm with the corneal apex as the center.Meanwhile,Using Pentacam analysis system to measure the corneal topography parameters include front K2(D),front Kmax(D),back k2(D),TCT(μm),corneal vertex thickness(μm),PCT(μm),PPIAvg,ARTmax,Df,Db,Dp,Dt,Da,D,ISV,IHA,IVA,IHD,KI,Rmin and CKI.The difference of corneal densitometry between the two groups was compared by covariance analysis.Person’s correlation test or Spearman’s correlation test was used to determine the correlations between the corneal densitometry and the corneal topography parameters.The receiver operating characteristic(ROC)curve and area under the curve(AUC)were performed to evaluate the diagnostic value of corneal densitometry and corneal topography parameters for keratoconus.Results: Except that the optical density of each layer of cornea in the diameter range of6～10mm was not statistically different between the two groups(all P>0.05),the rest of each layers in different diameters,especially 0～2mm and 2-6mm was higher than that of the control group(all P<0.05).There were statistically significant differences between the two groups of corneal topography parameters(all P<0.001).The ROC diagnostic curves was made using the corneal densitometry values and corneal topography parameters in different diameter ranges as diagnostic indicators.It demonstrated that the AUC was larger in the diameter of 0-2mm including the anterior layer,middle layer and total layer than that of 2-6mm in each layer,and the AUC Both were> 0.6 as well as the difference was statistically significant(all P<0.05).In which the anterior layer in the 0-2mm zone showed the largest one with an AUC of 0.849,a cut-off value of 15.55,a sensitivity of 75.4%,a specificity of84.3% and the 95% confidence interval was 0.799～0.889(P<0.001),and the diagnostic efficiency was the best.Except for IHA(AUC>0.7),anterior K2,Db,Dt,CKI(all AUC>0.8),the AUC values of other corneal topography parameters were all greater than 0.9.Among them,ISV showed the largest one with an AUC of 0.970,a cut-off value of 22.5,a sensitivity of 90%,a specificity of 96.6% and the 95% confidence interval was 0.949～0.991(P<0.001)in a ROC analysis using corneal topography parameters as diagnostic indicators to discriminate eyes with keratoconus from normal.The anterior Kmax,PPIAvg,Df,Db,Dp,Dt,D,ISV,and IHD are significantly positively correlated with the keratoconus group’s anterior,middle and total corneal densitometry values within the 0-2mm zone.The anterior K2 are significantly positively correlated with the keratoconus group’s anterior,middle and posterior corneal densitometry values within the 0-2mm zone.IVA is significantly positively correlated with the corneal densitometry of the anterior and total corneal in the 0-2mm zone,while TCT is significantly negatively correlated with the keratoconus group’s anterior,middle and total corneal densitometry values within the 0-2mm zone.Conclusion: Compared to normal population,the optical density of each layer of the cornea in the central area of keratoconus is higher,that is,the corneal transparency is lower.Meanwhile,corneal densitometry of anterior 0-2mm in the ROC curve has the highest sensitivity and specificity.And the corneal densitometry value in the 0-2mm zone is significantly related to most corneal topography parameters.The increase of densitometry in the anterior cornea of central zone could have certain diagnostic value for early keratoconus. |
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