External validation of cut-off points for foveal thickness taking into account the intraretinal fluid using optical coherence tomography to diagnose diabetic macular oedema

Background In late 2015, cut-off points were published for foveal thickness to diagnose diabetic macular oedema taking into account the presence of intraretinal fluid using optical coherence tomography (OCT) in primary care patients (90 µm in the presence of intraretinal fluid and 310 µm otherwise). Methods This cross-sectional observational study was carried out on 134 eyes of diabetic patients treated in specialised ophthalmology services in a Spanish region in 2012–2013, to externally validate the aforementioned cut-off points. The main variable (Clinical Standard) was the diagnosis of macular oedema through indirect ophthalmoscopy and posterior segment slit-lamp biomicroscopy. As validation variables, both the foveal thickness and the presence of intraretinal fluid obtained by OCT were used. Validation was performed using bootstrapping by calculating the area under the ROC curve (AUC), sensitivity, specificity, positive likelihood ratio (PLR) and negative likelihood ratio (NLR). Results Forty-one eyes presented diabetic macular oedema (30.6%). The bootstrapping validation parameters were: AUC, 0.88; sensitivity, 0.75; specificity, 0.95; PLR, 14.31; NLR, 0.26. These values were very similar to those of the original publication. Conclusion We have externally validated in specialised care patients the cut-off points published for the diagnosis of diabetic macular oedema. We suggest that others carry out validation studies in their communities.