Repeatability of Ophtha TOP in measuring corneal parameters and its agreement with Pentacam

Authors:Yu Shasha,  Song Hui,  Tang Xin
DOI: 10.3760/cma.j.issn.2095-0160.2016.12.014
Published 2016-12-10
Cite as Chin J Exp Ophthalmol, 2016,34(12): 1116-1120.

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Accurate measurement of corneal refractive parameters plays an important role in the diagnosis of eye diseases, design of refractive surgery and calculation of intraocular lens (IOL) power.Ophtha TOP is a new IOL calculator, so it is necessary to evaluate the repeatability and accuracy of Ophtha TOP in measuring corneal refractive parameters.


This study was to evaluate the repeatability of Ophtha TOP in measuring corneal refractive status in normal eyes and determine the agreement of the measuring outcomes between Ophtha TOP and Pentacam in pre-surgery cataract eyes.


A reliability evaluation method of diagnosis test was performed from September 2013 to October 2014.Sixty eyes of healthy volunteers aged (30.83±8.66) years old were examined in Tianjin Eye Hospital with Ophtha TOP for more than 5 times to evaluate the stability in measuring corneal refractive parameters.Corneal refractive parameters were measured by both Ophtha TOP and Pentacam for more than twice in 30 pre-surgery cataract eyes to assess the agreement with Pentacam.Keratometry and astigmatism parameters were recorded, including the flattest meridian (Kf), steepest meridian (Ks), mean keratometry (Km) and the astigmatism at J0 and J45.Intra-class correlation coefficients (ICC), repeatability (2.77Sw) and coefficient of variation (CoVs) were used to assess the stability of Ophtha TOP, and Bland-Altman graphs were adopted to value the consistency of measuring outcomes between Ophtha TOP and Pentacam.This study complied with Helsinki declaration, and written informed consent was obtained from each patient prior to any medical examination.


The ICC of Ks, Kf, Km, J0 and J45 by Ophtha TOP were all ≥0.90, and 2.77Sw were all ≤0.36, The CoVs of Kf, Ks, Km by Ophtha TOP were all ≤0.30.The measuring values of Kf, Ks and Km were significantly higher in the Ophtha TOP than those in the Pentacam, with the mean differences (0.18±0.28)D, (0.24±0.29)D and (0.21±0.26)D, respectively(t=3.48, 4.50, 4.49, all at P=0.00). The mean difference of the J0 was (0.07±0.21)D and that of the J45 was (-0.02±0.18)D between Ophtha TOP and Pentacam, showing insignificant differences between them (both at P>0.05). Bland-Altman graphs revealed that the 95% limit of agreement (LoA) of Kf, Ks and Km between the two methods was -0.37 D to 0.73 D , -0.33 D to 0.81 D and -0.30 D to 0.72 D, respectively, and that of J0 and J45 was -0.34 D to 0.48 D and -0.37 D to 0.33 D, respectively.


Ophtha TOP shows an excellent repeatability.Compared with Pentacam, Ophtha TOP presents a good consistence for measurement of the corneal astigmatism and moderate consistence for corneal curvature.

Key words:

Biometry/methods; Diagnostic techniques, ophthalmological/instrumentation; Corneal topography/methods; Reproducibility of results; Agreement; Astigmatism/diagnosis

Contributor Information

Yu Shasha
Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Institute, Tianjin Eye Hospital, Clinical College of Ophthalmology, Tianjin Medical University, Tianjin 300020, China
Song Hui
Tang Xin
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Updated: February 21, 2023 — 2:30 am