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To the Editor:
We read with great interest the article by Cobos et al1 entitled “Incidence and relation with anatomical and functional variables of postoperative macular displacement in rhegmatogenous retinal detachment” published in Retina 2016;36:957–961. The authors prospectively investigated the effect of macular displacement on retinal function, which is a welcome report, given the high reported incidence of postoperative retinal displacement.1–3 They found that 60% (12/20) eyes had evidence of retinal displacement on Topcon autofluorescence imaging and that no differences were found in multifocal electroretinography measurements between those with or without retinal displacement. This is certainly of interest, but we have a number of observations to make.
The authors report that their cohort of patients included 12 macula-on detachments and 8 macula-off detachments. Evidence of retinal displacement is then reported in 60% (12/20 eyes) at 3 months after surgery, but we are not informed as to where the retinal displacement occurred. Evidence from previous studies suggests that macula displacement and postoperative distortion are more common in macula-off when than in macula-on retinal detachments.2,3 It would therefore be helpful if the authors could specify in how many patients displacement was seen within the macula, rather than more peripherally. For patients in whom the macula was not affected by displacement, one would expect there to be little effect on visual acuity, central multifocal electroretinogram, and stereopsis. What is of interest, however, is whether macula displacement was associated with compromised visual function; and indeed, the number of patients who were judged preoperatively to be macula-on who postoperatively had evidence of macula displacement.
From a statistical perspective, the authors state that the association between multifocal electroretinography voltage, best-corrected visual acuity, and stereopsis and retinal displacement was assessed using the Wilcoxon test. When investigating multiple associations in this way, it may have been more appropriate to use a regression model. The authors also used a Fisher exact test to investigate the relationship between macular involvement and multifocal electroretinography voltage; was the voltage data therefore converted to categorical values for this test?
Finally, the study also states that patients were positioned face down immediately after surgery, but it would be of interest to know for how long they were advised to adopt this posture. We would caution against the suggestion that face-down positioning does not have a role in preventing displacement on the basis of this study or the available literature because there is no consistency as to how long that posture has been adopted or whether adequate comparison with other postoperative positions have been made. Nonetheless, this is a welcome study investigating the incidence of a potentially important postoperative complication and its effect on macular function.
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