Cystoid macular edema after femtosecond laser–assisted versus phacoemulsification cataract surgery: Letter 1

Abstract

We read with interest the findings of Ewe et al.1 We respectively suggest that the results do not support the stated hypothesis and conclusions and might be interpreted in an alternative manner. The study design was to evaluate the incidence of cystoid macular edema (CME) between the 2 groups, and the study found that there was no statistically significant difference. The authors performed a further subgroup analysis of femtosecond laser–assisted cataract surgery cases after a software upgrade and again found no statistical difference in the incidence of CME. These findings are consistent with previously published prospective studies that similarly described no difference in the incidence of clinical CME between femtosecond laser–assisted cataract surgery and manual surgery.2,3 Despite no statistical difference and that the smaller cohort effectively reduced the potential power of the results, the authors concluded that “CME might be a subthreshold retinal injury safety signal.” No published study has indicated that the incidence of clinical CME is significantly higher after femtosecond laser–assisted cataract surgery, and one cannot therefore use these results to speculate about possible damage to the retina by all makes or any make of femtosecond laser. The sentence stating “CME is now typically less common because of prophylactic pre- and postoperative topical NSAID [nonsteroidal antiinflammatory drug] use combined with postoperative topical steroids” can also be challenged. The reference used is from a 1996 study4 that evaluated angiographic CME in groups receiving diclofenac or a placebo. There are several concerns referencing this study; namely, the small sample and the corresponding high incidence of intraoperative complications. Of clinical relevance to 2016, up to 76% of patients in each group had extracapsular surgery by the attending surgeon or by residents in training. It is therefore difficult to undertake a meaningful comparison with patients having laser-assisted cataract surgery today. Current data are available. Tzelikis et al.5 showed in a randomized prospective trial that NSAIDs were not efficacious in preventing macular edema. The authors hypothesize that thermal damage might be intensified as a result of prolonged elevated pressure as docking “reduces cooling due to impaired perfusion.” This was not measured during the study, was not a primary or secondary endpoint, and therefore is speculation. Hypotheses should be carefully phrased, especially when they are not based on study findings. The statement is even more speculative because previous data with the same femtosecond laser found only a minimal increase in intraocular pressure (IOP) and most cases of CME in this study occurred after the software upgrade, which would logically decrease the amount of time the pressure was applied. In conclusion, the study’s purpose was to compare the incidence of CME between femtosecond laser–assisted cataract surgery and manual cataract surgery. It found no statistical difference between the 2 groups. It was not designed to show the effect of NSAIDs on either group, nor did it measure IOP before, during, or after laser application. It did not measure retinal blood flow or function or the heat generated by the laser. As such, speculation in the abstract and conclusion that “[i]ncreased CME might be a subthreshold retinal injury safety signal after femtosecond laser pretreatment” is not supported by the design or results in the study.