Reproducibility of Spectral-Domain Optical Coherence Tomography Retinal Thickness Measurements and Conversion to Equivalent Time-Domain Metrics in Diabetic Macular Edema

Abstract

Diabetic Retinopathy Clinical Research Network Writing Committee IMPORTANCE Understanding measurement variability and relationships between measurements obtained on different optical coherence tomography (OCT) machines is critical for clinical trials and clinical settings.OBJECTIVE To evaluate the reproducibility of retinal thickness measurements from OCT images obtained by time-domain (TD) (Stratus; Carl Zeiss Meditec) and spectral-domain (SD) (Cirrus; Carl Zeiss Meditec, and Spectralis; Heidelberg Engineering) instruments and formulate equations to convert retinal thickness measurements from SD-OCT to equivalent values on TD-OCT. DESIGN, SETTING, AND PARTICIPANTSA cross-sectional observational study was conducted in private and institutional practices. Persons with diabetes mellitus who had at least 1 eye with central-involved diabetic macular edema, defined as Stratus central subfield thickness (CST) of 250 μm or greater, participated. An additional normative cohort (individuals with diabetes but without diabetic macular edema) was enrolled. Each study eye underwent 2 replicate Stratus scans followed by 2 replicate Cirrus or Spectralis scans (real-time image registration used) centered on the fovea. MAIN OUTCOMES AND MEASURESOptical coherence tomography CST and macular volume. RESULTSThe Bland-Altman coefficient of repeatability for relative change in CST (the degree of change that could be expected from measurement variability) was lower with Spectralis (7%) compared with Cirrus (14%) and Stratus (12% and 15% within Cirrus/Stratus and Spectralis/Stratus groups, respectively). For each cohort, the initial Stratus CST was within 10% of the replicate Stratus measurement nearly all of the time; the conversion equations predicted a Stratus CST within 10% of the observed thickness 86% and 89% of the time for Cirrus/Stratus and Spectralis/Stratus groups, respectively, which is similar to the agreement on Stratus test-retest. The Bland-Altman limits of agreement for relative change in CST between machines (the degree of change that could be expected from measurement variability [combining within and between instrument variability]) were 21% for Cirrus and 19% for Spectralis when comparing predicted vs actual Stratus measurement.CONCLUSIONS AND RELEVANCE Reproducibility appears to be better with Spectralis than with Cirrus and Stratus. Conversion equations to transform Cirrus or Spectralis measurements to Stratus-equivalent values, within 10% of the observed Stratus thickness values, appear feasible. Central subfield thickness changes beyond 10% when using the same machine or 20% when switching machines, after conversion to Stratus equivalents, are likely due to a change in retinal thickness rather than measurement error.

Are we making good use of our public resources? The false-positive rate of screening by fundus photography for diabetic macular oedema

“…14 The DRCR Network also showed that sd-OCT measurement can be reliably converted to standard Stratus time-domain OCT measurement with conversion equations. 13 If CMT of 250 µm in time-domain OCT is converted to the sd-OCT, it will range from 290.2 µm to 313.4 µm. We chose 300 µm as the cut-off value for the upper limit of normal macular thickness to distinguish abnormal from normal because our Carl Zeiss Cirrus OCT is a sd-OCT.…”

“…6 In recent years, there has been a move towards the use of newer treatment modalities, such as intravitreal injection of anti-vascular endothelial growth factor (VEGF) agents that are superior to the traditional laser treatment in the management of CSME. [7][8][9][10][11][12][13][14] Screening for DR has been proven to be cost-effective in reducing significant vision loss by early detection of the pathology. [15][16][17] This will subsequently reduce the financial burden caused by vision complications of DR on the health care system.…”

A Crossover Design for Comparative Efficacy

“…Following repair of the Cirrus, both Cirrus and Spectralis OCT scans were captured at 150 subsequent participant visits, enabling development and validation of a linear conversion function for CSMT from Spectralis to Cirrus, similar to work done previously by the DRCR.net. 22 Prediction error of the conversion function was evaluated using a bootstrap cross-validation routine and was estimated to be 8.4 μm (95% CI [8.4, 8.6]). Spectralis values were converted and utilized as Cirrus CSMT values for the 12% of key visits at which the Cirrus scan was not performed.…”

Recent advancements in diabetic retinopathy treatment from the Diabetic Retinopathy Clinical Research Network

“…The DRCR Network has published 2 manuscripts in the last year that provide some metrics for the conversion of SD-OCT data from the Cirrus (Carl Zeiss Meditec), the Spectralis (Heidelberg Engineering), and the RTVue (Optovue) to TD-OCT (Carl Zeiss Stratus) standards. [11,12] The analysis provided by the network is useful in evaluating and comparing results across trials and developing machine-specific thresholds on SD-OCT for interventions in subsequent clinical trials.…”