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Brief Report |

Comparison of In Vivo Confocal Microscopy, Ultrasonic Pachymetry, and Scheimpflug Topography for Measuring Central Corneal Thickness

Soundaram MeenakshiSundaram, MD1; Aalia Rasool Sufi, MD1; N. Venkatesh Prajna, MD1; Jeremy D. Keenan, MD, MPH2,3
[+] Author Affiliations
1Department of Cornea and External Diseases, Aravind Eye Hospital, Madurai, India
2Francis I. Proctor Foundation, University of California, San Francisco
3Department of Ophthalmology, University of California, San Francisco
JAMA Ophthalmol. 2016;134(9):1057-1059. doi:10.1001/jamaophthalmol.2016.2183.
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Importance  In vivo confocal microscopy could be useful in cases of fungal or acanthamoeba keratitis to determine the depth of infectious elements, but its accuracy in determining corneal thickness relative to more traditional techniques has not been well characterized.

Observations  In this cross-sectional observational case series, central corneal thickness was determined by in vivo confocal microscopy, ultrasonic pachymetry, and Scheimpflug topography in 47 normal corneas and 23 keratoconic corneas from November 2014 to July 2015. Analyses undertaken from July 2015 to August 2015 showed that confocal microscopy overestimated the central corneal thickness in nonkeratoconic eyes, measuring on average 5 μm thicker (95% limits of agreement [LoA], 54-64) than ultrasonic pachymetry and 14 μm thicker (95% LoA, 47-76) than Scheimpflug topography. The bias was more pronounced in keratoconic eyes, where confocal microscopy overestimated central corneal thickness by 50 μm relative to ultrasonic pachymetry (95% LoA, 77-178) and 52 μm relative to Scheimpflug topography (95% LoA, 69-174).

Conclusions and Relevance  Confocal microscopy overestimated central corneal thickness relative to the other instruments, but the magnitude of the differences were small, especially in nonkeratoconic eyes. This level of measurement bias is acceptable to us for determining the depth of fungal filaments and acanthamoeba cysts in infectious keratitis.

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Bland-Altman Plots for Pairwise Comparisons of 3 Tests of Central Corneal Thickness

The dotted line represents the mean difference between the 2 tests, and the shaded area represents the 95% limits of agreement. CCT indicates central corneal thickness; IVCM, in vivo confocal microscopy; USG, ultrasonic pachymetry.

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