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Editors Selection IGR 12-3
Optical Coherence Tomography: Agreement RNFL in three SD-OCT instruments
Comment by Luciana Alencar on:
27805 Agreement among spectral-domain optical coherence tomography instruments for assessing retinal nerve fiber layer thickness, Leite MT; Rao HL; Weinreb RN et al., American Journal of Ophthalmology, 2011; 151: 85-92
In the past years, we have witnessed a boom of new spectral-domain OCT (SD-OCT) imaging devices. Besides the obvious advantages of high-resolution and the benefits of competition, we now face a different problem: can we use these systems interchangeably? Leite et al. (180) have conducted an important study to assess the agreement of retinal nerve fiber layer (RNFL) thickness measurements among three SD-OCT instruments in healthy, suspects and glaucomatous individuals (n = 330 eyes). Patients were examined on the same visit using the RTVue, the Cirrus, and the Spectralis. The authors showed that there were significant differences in the measurements obtained by each instrument for the average and for the sectors' analyses. They observed consistently thicker measurements for RTVue, when compared to Cirrus and Spectralis. Spectralis had thicker measurements than Cirrus for average, temporal, and inferior thicknesses, but thinner measurements for the nasal quadrant. In addition, they showed that the degree of disagreement between instruments was variable, depending on the actual thickness. Consequently, as the authors point out, different stages of disease will be associated with different levels of agreement. It is also possible to assume a variable floor effect, which could explain why differences grow as the RNFL becomes thinner. Of note, eyes with worse visual fields, worse myopia, and greater axial length had even thinner RNFL with the Spectralis.
Direct comparisons should not be made between results obtained with different instruments
Among the factors that influenced the agreement of at least one pairwise comparison, they found age, disease severity, spherical equivalent, and axial length. Disc area and race did not affect the agreement. The authors conclude that measurements from these instruments should not be used interchangeably, and histological studies are needed to determine which one is more accurate. What does this mean for the practicing clinician? Direct comparisons should not be made between results obtained with different instruments, and during follow-up, a patient may benefit from repeated exams in the same SD-OCT.
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