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Measurement bias between optical coherence tomography instruments in diabetic macular edema- implications for treatment

Poster Details

First Author: A.Kidess UK

Co Author(s):    D. Trivedi   A. El Salloukh   P. Dutt   P. Keane   M. Tsaloumas   A. Denniston   0   0 0   0 0   0 0   0 0

Abstract Details


The National Institute for Health and Care Excellence (NICE) has recommended the use of ranibizumab for diabetic macular oedema (DMO) in the presence of a central macular thickness (CMT) of 400 µm or more at the beginning of the treatment. However, the guidelines did not specify which optical coherence tomography (OCT) device(s) should be used for this assessment.The purpose of the study was to determine the extent to which the type of OCT device used affects the value of CMT measured when assessing DMO in a ‘real-world’ setting, and whether this might affect patient access to treatment in the UK.


The study was undertaken at the Queen Elizabeth Hospital in Birmingham


50 patients (92 eyes) with suspected DMO in at least one eye were randomly selected to undergo OCT scans using both 3D OCT-1000 (Topcon) and Spectralis OCT (Heidelberg) on the same day. Matched macular-centered scans were obtained in 92 eyes; scans were not possible in 8 eyes due to media opacity or problems with patient fixation.


The mean (standard deviation) CMT in this cohort was 277 (88) μm with a range of 544 μm using the 3D OCT-1000, and 305 (91) μm with a range of 530 μm using the Spectralis OCT. Comparing the two instruments in our cohort using a Bland–Altman analysis, there was a bias of +10.4 μm when using the Spectralis vs the 3D OCT-1000 with a standard deviation of 10.0, and 95% limits of agreement of -9.2 to 30.1 μm. There were two patients who were eligible for treatment (CMT>400 μm) when measured by Spectralis but not eligible (CMT<400 μm) when measured by 3D OCT-1000.


It is important to recognise the differences between instruments when using an absolute threshold for treatment such as the 400 μm CMT level defined by NICE. ‘Real-world’ studies demonstrating repeatability and inter-instrument variability in defined patient cohorts may help inform these decisions.

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