Sir,
We highly appreciate the comments of Dr Engelbert et al on our recently published article.1 We agree with the observations made by Dr Engelbert et al that the measurement of retinal thickness (RT) with optical coherence tomography (OCT) will vary depending on the outer retinal boundary delineated by each instrument. Therefore, appropriate boundaries for thickness determination should be set, if allowed by the instrument.
The outer boundary used by Spectral SLO/OCT can be hypothesized according to the reported data about RT in normal eyes, as measured with different spectral OCT models. Mean RT, as measured with spectral domain SLO/OCT, was 281±88 μm before exclusion of the artefacts and 277.1±66 μm after their removal. In a recent report by Han et al,2 Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany) generated a similar RT measurement (279±26 μm). According to previously described thickness measures of specific outer retinal layers, Spectralis OCT likely sets the outer retinal boundary for RT measurement at the junction of Bruch's membrane and the choriocapillaris; the same outer boundary could be used by Spectral SLO/OCT.
References
Forte R, Cennamo GL, Finelli ML, de Crecchio G . Comparison of time domain Stratus OCT and spectral domain SLO/OCT for assessment of macular thickness and volume. Eye 2008; 12 December 2008 [E-pub ahead of print].
Han IC, Jaffe GJ . Comparison of spectral spectra and time-domain optical coherence tomography for retinal thickness measurements in healthy and diseased. Am J Ophthalmol 2009; 4 February 2009 [E-pub ahead of print].
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Forte, R., Cennamo, G., Finelli, M. et al. Response to Dr Engelbert et al. Eye 24, 193–194 (2010). https://doi.org/10.1038/eye.2009.59
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DOI: https://doi.org/10.1038/eye.2009.59