Measurement bias between optical coherence tomography instruments can affect access to treatment: a new lottery

Andrej Kidess, Adonis El Salloukh, Poonam Dutt, Pearse A Keane, Marie D Tsaloumas, Alastair K Denniston

Queen Elizabeth Hospital Birmingham, University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK

It is with great interest that we read the publication entitled "Critical appraisal of ranibizumab in the treatment of diabetic macular edema" by Stewart.¹ The author emphasized the importance of the vascular endothelial growth factor (VEGF) in the pathophysiology of diabetic macular edema (DME). As highlighted in that article, the anti-VEGF ranibizumab is a superior treatment compared to traditional argon photocoagulation, leading to better anatomical and functional results.
In April 2013, the National Institute for Health and Care Excellence (NICE) of the UK approved the use of ranibizumab as a treatment option to treat diabetic macular edema of the eye if it has a central macular thickness (CMT) of 400 μm or more at the beginning of the treatment.² The guidelines did not specify which optical coherence tomography (OCT) device(s) should be used for this assessment. This is important as, although good consistency has been shown in using the same instrument, there is a known divergence in CMT measurements between different instruments.^3–6 For example, the Spectralis^® OCT (Heidelberg Engineering; Carsbad, CA, USA) generally shows higher values of mean CMT in a normal eye compared to most other instruments, in part due to the retinal segmentation algorithm that it employs.⁴ We hypothesized that similar (or increased) differences might be observed in DME, and that for those countries (such as the UK) where a fixed CMT is used to define eligibility for treatment, the "lottery" of OCT instruments may influence eligibility.

View original paper by Stewart.