OSLI Retina

September 2018

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654 Ophthalmic Surgery, Lasers & Imaging Retina | Healio.com/OSLIRetina ■ C O R R E S P O N D E N C E ■ Letter to the Editor: Efficacy of the Intravitreal Sustained-Release Dexamethasone Implant for DME Refractory to Anti-VEGF Therapy: Meta-Analysis and Clinical Implications Dear Editor, We have significant concerns regarding the meth- odology used in the Khan et al. 1 meta-analysis and the subsequent size of treatment effect reported. In par- ticular, the result stating that "patients treated with dexamethasone implants for diabetic macular edema (DME) refractory to anti-VEGF [vascular endothelial growth factor] therapy gained a mean of four lines (20 logMAR letters)" appears inaccurate, as none of the included studies reported a treatment effect of the same magnitude. There are several methodological weaknesses highlighted below. MISINTERPRETATION OF THE STANDARDIZED MEAN DIFFERENCE Figure 3 of the paper in question plots the "stan- dard difference in means," but this effect measure is not clearly defined in the methods section. If it is the "standardized mean difference," then this measure of effect is the size of the intervention effect in each study relative to the variability observed in that study and is reported in units of standard deviation. 2 We suspect the authors have mistakenly assumed the val- ue of 0.471 has units of logMAR (rather than units of standard deviation) and hence have incorrectly esti- mated a value of 23 logMAR letters as the mean visual acuity gain achieved. STUDY INCLUSION AND HANDLING We question the wisdom of combining results from such diverse study designs. 3 The report would have benefited from more detailed reporting of design characteristics of the included studies, the data used to calculate the measure of effect, and justification for the judgements on the risk of bias. Some studies also appear to be included incorrect- ly. Using the published references, the authors have included in their meta-analysis two studies 4,5 where one is a subanalysis of the other. Another is from the GENEVA group evaluating efficacy of dexamethasone (Ozurdex; Allergan, Dublin, Ireland) treating macular edema associated with branch or central retinal vein occlusion, 6 and another is a study of four children treated for diseases such as Coats' disease, macular telangiectasia, and uveitis. 7 PRIOR TREATMENT The authors reported "all patients were treated for recalcitrant diabetic macular edema with at least six prior treatments of intravitreal anti-VEGF therapy." They reported "the total number of patients studied was 3,859." On review of the included studies, we struggle to reach this number and precisely say how many injections patients received. In view of the above methodological limitations, we have concerns with the conclusions drawn. 1 Charles Hennings, MBBS, MEng 2 Jennifer Evans, BA (Cantab), MSc, PhD 1 Hemal Mehta, MA, FRCOphth 1 Royal Free London NHS Foundation Trust London, UK 2 International Centre for Eye Health London School of Hygiene and Tropical Medicine London, UK REFERENCES 1. Khan Z, Kuriakose RK, Khan M, Chin EK, Almeida DRP. Efficacy of the intravitreal sustained-release dexamethasone implant for diabetic macular edema refractory to anti-vascular endothelial growth factor therapy: Meta-analysis and clinical implications. Ophthalmic Surg La- sers Imaging Retina. 2017;48(2):160-166. 2. Cochrane Library. The standardized mean difference. Co- chrane Database of Systematic Reviews. http://handbook-5-1.co- chrane.org/chapter_9/9_2_3_2_the_standardized_mean_difference. htm. Accessed March 21, 2018.

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