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Kim, Li, Lee, and Yoon: Measurement of Corneal Power and Astigmatism Using Placido-based Videokeratography and Comparison with Other Keratometers
Original Article

J Korean Ophthalmol Soc 2016;57(12):1874-1881.

Published online: 25 September 2016

DOI: https://doi.org/10.3341/jkos.2016.57.12.1874

Measurement of Corneal Power and Astigmatism Using Placido-based Videokeratography and Comparison with Other Keratometers

Yung Hui Kim, MD, Ying Li, MD, Hyo Seok Lee, MD, Kyung-Chul Yoon, MD, PhD

Department of Ophthalmology, Chonnam National University Medical School, Gwangju, Korea

Address reprint requests to Kyung-Chul Yoon, MD, PhD Department of Ophthalmology, Chonnam National University Hospital, #42 Jebong-ro, Dong-gu, Gwangju 61469, Korea Tel: 82-62-220-6753, Fax: 82-62-227-1642 E-mail: kcyoon@jnu.ac.kr

Received 18 August 2016       Revised 20 September 2016       Accepted 22 November 2016

Copyright © 2016 Korean Ophthalmological Society

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

In the present study, the repeatability and reproducibility of the corneal power and astigmatism measurements using placido-based video keratography were evaluated and the agreement with other keratometers were compared.

Methods

This prospective study included 45 patients (45 eyes) scheduled to undergo cataract surgery between November 2015 and January 2016. Three sets of corneal power and astigmatism were measured using placido-based video keratometer (Keratograph® 5M), automatic keratometer (KR-8900®), manual keratometer (B&L manual keratometer®), Placido-scanning-slit keratometer (ORBscan II®), Scheimpflug keratometer (Pentacam®), and low coherence interferometry (Lenstar LS900®). Reliability of each device was analyzed using the coefficient of variation, standard deviation and intraclass correlation coefficient. Repeated measures analysis of variance was used to analyze the interdevice comparison of mean absolute difference. The agreement between the devices was evaluated with 95% limits of agreement (LoA) and Bland-Altman plots.

Results

The mean corneal power, astigmatism and power vector analysis (J0, J45) were not significantly different among devices (p > 0.05). In the Bland-Altman plot analysis, the 95% LoA of corneal power, J0, and J45 when comparing Keratograph® 5M with others ranged from −0.78 to 0.55 D, from −0.42 to 0.45 D, and from –0.39 to 0.47 D, respectively.

Conclusions

Keratograph® 5M showed good repeatability and reproducibility of corneal power and astigmatism measurements and was interchangeable with other keratometers.

Keywords: Astigmatism, Corneal power, Keratograph, Keratometer, Placido-based

References

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Figure 1.
Keratometric measurements by several keratometers. Mean corneal power (A) and astigmatism (B) measured by Keratograph® 5M and other keratometers. No statistically significant differences (p > 0.05).
jkos-57-1874f1.tif
Figure 2.
Disagreement in flat axis location are scattered according to magnitude of corneal astigmatism between Kerato-graph® 5M and other keratometers. Note that when the astigmatism is more than 1.5 diopters (vertical line), the difference is comparable.
jkos-57-1874f2.tif
Figure 3.
Scatter plot of power vector analysis (J0, J45) of astigmatic magnitude measured by Keratograph® 5M and other keratometers. There was no significant differences in the astigmatic components (p > 0.05). J0 = Jackson cross-cylinder, axes at 90 and 180 degrees; J45 = Jackson cross-cylinder, axes at 45 degrees and 135 degrees; D = diopter; sim K = simulated keratometry.
jkos-57-1874f3.tif
Figure 4.
Comparison of corneal power and astigmatism among keratometers. Bland-Altman plots which show differences in corneal power (A), J0 (B) and J45 (C) measurements between Keratograph® 5M and other keratometers. The solid line indicates the mean difference. The upper and lower dotted lines indicate the 95% limits of agreement. There was no significant difference of corneal power, J0, and J45 between Keratograph® 5M and other keratometers (p > 0.05). J0 = Jackson cross-cylinder, axes at 90 and 180 degrees; J45 = Jackson cross-cylinder, axes at 45 degrees and 135 degrees.
jkos-57-1874f4.tif
Table 1.
Reliability of corneal power and astigmatism measurements
  Mean K (D) CoV (%) ICCs Astigmatism (D) CoV (%) ICCs
Keratograph® 5M 44.09 ± 1.54 0.22 0.992 0.95 ± 0.15 12.0 0.981
KR-8900® 44.08 ± 1.60 0.25 0.989 0.99 ± 0.21 12.5 0.912
Pentacam® 44.17 ± 1.69 0.27 0.976 0.93 ± 0.17 14.7 0.976
ORB scan II® Sim K 44.38 ± 1.41 0.31 0.991 0.99 ± 0.23 12.3 0.948
ORB scan II® 3 mm zone K 44.32 ± 1.48 0.27 0.953 1.03 ± 0.16 14.2 0.883
B&L Mannual keratometer® 44.04 ± 1.55 0.30 0.990 0.90 ± 0.11 11.3 0.937
Lenstar LS900® 44.22 ± 1.61 0.42 0.964 1.05 ± 0.26 10.5 0.899

Values are presented as mean ± SD unless otherwise indicated. K = corneal power; CoV = coefficient of variation; ICCs = intraclass correlation coefficients.

Table 2.
Precision and repeatability of corneal power and astigmatism measurements by several keratometers
  Corneal power
 Astigmatism
MAD (D) Sw (D) Precision Repeatability MAD (D) Sw (D) Precision Repeatability
Keratograph® 5M 0.115 0.097 0.190 0.269 0.098 0.114 0.223 0.316
KR-8900® 0.101 0.112 0.220 0.310 0.104 0.124 0.243 0.343
Pentacam® 0.127 0.120 0.235 0.332 0.086 0.137 0.269 0.379
ORB scan II® sim K 0.119 0.137 0.269 0.379 0.094 0.122 0.239 0.338
ORB scan II® 3 mm zone K 0.135 0.121 0.237 0.335 0.124 0.146 0.286 0.404
B&L manual keratometer® 0.181 0.131 0.257 0.363 0.089 0.102 0.200 0.283
Lenstar LS900® 0.136 0.185 0.363 0.512 0.101 0.110 0.216 0.305

Repeated measures analysis of variance (RM-ANOVA): No statistically significant values (p > 0.05). MAD = mean absolute difference; Sw = within subject standard deviation; Precision = 1.96Sw; Repeatability = 2.77Sw.

Table 3.
Comparison of corneal power and power vector analysis (J0, J45) measurements among 7 keratometric devices
  Corneal power (D)
 J0 (D)
 J45 (D)
Difference 95% LoA p-value* Difference 95% LoA p-value* Difference 95% LoA p-value*
Keratograph® 5M vs. KR-8900® 0.01 ± 0.21 –0.40∼0.42 0.822 0.08 ± 0.19 –0.29∼0.45 0.535 0.04 ± 0.22 –0.39∼0.47 0.616
Keratograph® 5M vs. Pentacam –0.08 ± 0.32 –0.71∼0.55 0.453 0.06 ± 0.14 –0.21∼0.33 0.486 0.03 ± 0.15 –0.26∼0.32 0.511
Keratograph® 5M vs. ORBscan II® sim K –0.29 ± 0.25 –0.78∼0.20 0.057 0.01 ± 0.22 –0.42∼0.44 0.932 –0.04 ± 0.17 –0.37∼0.29 0.348
Keratograph® 5M vs. ORBscan II® 3 mm zone K –0.23 ± 0.22 –0.66∼0.20 0.112 0.08 ± 0.16 –0.23∼0.39 0.399 0.07 ± 0.15 –0.22∼0.36 0.294
Keratograph® 5M vs. B&L manual keratometer® 0.05 ± 0.19 –0.32∼0.42 0.373 – – – – – –
Keratograph® 5M vs. Lenstar LS900® –0.13 ± 0.22 –0.56∼0.30 0.059 0.05 ± 0.20 –0.34∼0.44 0.732 –0.06 ± 0.14 –0.33∼0.21 0.317

Values are presented as mean ± SD unless otherwise indicated. Limits of agreement (LoA): p < 0.05, considered statistically significant.

* Repeated measures analysis of variance on ranks; 6 comparisons (RM-ANOVA): p < 0.05 is considered statistically significant.

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