J Korean Ophthalmol Soc.  2016 Dec;57(12):1874-1881. 10.3341/jkos.2016.57.12.1874.

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

• Kim YH
• Li Y
• Lee HS
• Yoon KC

• KMID: 2362704
• DOI: http://doi.org/10.3341/jkos.2016.57.12.1874

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 (Jâ‚€, Jâ‚„â‚…) were not significantly different among devices (p > 0.05). In the Bland-Altman plot analysis, the 95% LoA of corneal power, Jâ‚€, 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.

Keyword

Astigmatism; Corneal power; Keratograph; Keratometer; Placido-based

MeSH Terms

Astigmatism*
Cataract
Corneal Topography*
Humans
Interferometry
Loa
Prospective Studies

Figure

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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).

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  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.

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  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.

• 

  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.

Reference

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