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To the Editor:
We appreciate the opportunity to respond to the interesting comments made by Casswell et al regarding our article entitled “Incidence and relation with anatomical and functional variables of postoperative macular displacement in rhegmatogenous retinal detachment,” which was published in Retina in 2016.1 We thank Caswell et al for their thoughtful input.
In our study, we included 20 consecutive eyes with rhegmatogenous retinal detachment, 12 of which were macula-on and 8 macula-off. Retinal displacement was observed in 5 of the macula-on cases (42%) and 7 (87%) of the macula-off cases (P = 0.055). Based on our cut-off level (P < 0.05) for statistical significance, this finding was close to reaching statistical significance. Previous studies, with larger sample sizes, have demonstrated a significant association between retinal displacement and macula involvement.2,3 The most important causes of displacement are probably the small amount of subretinal fluid remaining in the posterior pole after surgery and the effect of the gas tamponade. In patients with a previously detached macula, fluid accumulates more easily than in patients with an attached macula; however, even in these cases, gravity could cause some fluid to slide toward the posterior pole. In our study, the retinal displacement was observed only within the vascular arcades, probably because this is where the autofluorescence image was focused; consequently, we did not assess peripheral retinal displacement.
We used the Wilcoxon test to perform the statistical analysis because our primary aim was to identify associations between the study variables; we did not seek to determine causality. The Fisher exact test was performed to analyze the relation between macular involvement and retinal displacement.
As Casswell et al point out, neither our study nor previous studies provide an adequate comparison between time and type of proper head positioning after rhegmatogenous retinal detachment surgery, and thus there is insufficient evidence to demonstrate that face-down positioning prevents retinal displacement. However, it is important to note that, in our study, the face-down position was implemented in the operating room immediately after the surgical intervention and maintained for 5 days; moreover, the percentage of eyes with retinal displacement in our study was comparable with previous reports2–4 in which face-down positioning was not implemented in the operating room. These findings suggest that it may not be essential to immediately implement face-down positioning, but we are aware that the data we have so far are not enough, and more studies are needed.
In conclusion, we agree with Caswell et al that, based on the currently available evidence, the best way to prevent retinal displacement after rhegmatogenous retinal detachment surgery is to recommend that patients maintain the face-down position. This position is important to ensure that the gas bubble pushes the retina against the retinal pigment epithelium in the posterior pole during the first days after surgery, thus minimizing the likelihood of postoperative retinal displacement.
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