Repeatability of Pentacam HR in measuring corneal topographic parameters of keratoconus patients

Objective  To investigate the repeatability of corneal topographic parameters with the Pentacam HR in patients with keratoconus of different severity.

Methods  A diagnostic test study was performed.A total of 120 eyes from 98 patients with subclinical keratoconus or keratoconus were enrolled at Henan Eye Hospital from January 2019 to March 2022.The patients were divided into subclinical keratoconus group, mild keratoconus group, moderate keratoconus group and severe keratoconus group, with 30 eyes in each group.An additional 30 eyes of 30 subjects undergoing refractive surgery were selected as a control group.Three consecutive Pentacam HR measurements were performed by the same clinician.The recordings included a total of 53 parameters in anterior corneal surface, posterior corneal surface, thickness, composite index, and corneal densitometry.The within-subject standard deviation (Sw), repeatability limit ( r) and tolerance index (TI) were calculated to evaluate the repeatability of the parameters between different groups.This study adhered to the Declaration of Helsinki and was approved by the Ethics Committee of Henan Eye Hospital (No.HNEECKY-2019[5]).All subjects were informed of the purpose and significance of the study and signed an informed consent form before enrollment.

Results  Compared with the control group, the TI of the subclinical, mild, moderate and severe keratoconus groups were 54.71%(29/53), 66.04%(35/53), 90.57%(48/53) and 94.34%(50/53), respectively, higher than 0.31.The steep keratometry (Ks), the maximum keratometry (Kmax) of the anterior corneal surface, the anterior corneal radius of curvature, the flat keratometry (Kf) of the posterior corneal surface, the posterior corneal radius of curvature (PRC), the thinnest corneal thickness (TCT), the average densitometry for the anterior 120 μm in the 0-2 mm area (A.0-2 mm), average densitometry for the anterior 120 μm in the 2-6 mm area (A.2-6 mm), average densitometry for the central tissue in the 0-2 mm area (C.2-6 mm), average densitometry for the total cornea in the 0-2 mm area (T.0-2 mm) and average densitometry for the total cornea in the 2-6 mm area (T.2-6 mm) showed good repeatability in the subclinical and mild keratoconus groups (TI<0.31).Kmax Zonal Mean 3 mm, posterior corneal surface mean keratometry, central keratoconus index showed good repeatability in subclinical, mild and moderate keratoconus groups.Kmax Zonal Mean 4 mm and Kmax Zonal Mean 5 mm showed good repeatability in all groups (TI<0.31).

Conclusions  For patients with subclinical and mild keratoconus, Kf of the posterior corneal surface, PRC and TCT are recommended to monitor disease progression.To monitor the condition of patients with moderate and severe keratoconus, we may focus on the detection of Kmax Zonal Mean 4 mm and Kmax Zonal Mean 5 mm.

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