We would like to comment some aspects of the manuscript by Okamoto and associates regarding the relationship between metamorphopsia and macular morphologic changes in patients who have undergone surgery for rhegmatogenous retinal detachment (RRD).
Interestingly, the authors report that 64% of the metamorphopsic eyes exhibited normal-appearing spectral-domain optical coherence tomography (OCT) findings. However, OCT images and metamorphopsia scores were obtained at variable intervals (6-12 months) after operation, so it is possible that substantial retinal morphologic abnormalities were already resolved by the time the images were taken. The chance of missing subtle abnormalities might have been further enhanced by the use of an OCT protocol consisting of only 5 horizontal and 5 vertical raster scans. Another limitation of the study is that the authors do not clarify if special attention was paid to check whether the central scan was centered on the fovea and whether the retinal abnormalities involving the central scan were considered more relevant than those observed elsewhere. This is important because alterations occurring at the fovea may have repercussions on the quality of vision, including metamorphopsia, more conspicuous than alterations involving other macular areas.
The authors speculate, but do not prove, that metamorphopsia in eyes with “normal-appearing OCT” might be related to unintentional retinal displacement, a complication clearly visualized using fundus autofluorescence (FAF) imaging (not recorded in this study). According to our experience, the rate of unintentional displacement, originally reported as high as 62% in association to cystic RRD managed with pars plana vitrectomy (PPV) and gas, is reduced by postoperative face-down posturing. In the present study, patients injected with gas were instructed to maintain a face-down position during the first postoperative week. Therefore, it is possible that at least some cases of unexplained metamorphopsia were actually related to subtle abnormalities that remained undetected on OCT rather than to retinal displacement.
Recently, we described that hyperreflective lesions formed by the folded hyperreflective bands constituted by the photoreceptor inner segment/outer segment (IS/OS) and by the external limiting membrane (ELM) lines, the so-called “outer retinal folds” (ORFs), are common findings after RRD repair with PPV and gas and relate to metamorphopsia evaluated by Amsler grid. ORFs tend to resolve spontaneously within 6 months or less from the operation, leaving behind sharply demarcated skip changes in reflectivity of the IS/OS line, the so-called “IS/OS skip reflectivity abnormalities” (RAs). There is no true loss or irregularity but rather skip reflectivity attenuation of the IS/OS line in the context of IS/OS skip RAs.
These abnormalities probably reflect morphologic changes and/or very subtle misalignment of the distal end of photoreceptors, are noticed in areas previously occupied by ORFs or pockets of subretinal fluid (both of which may cause metamorphopsia), and may be associated with metamorphopsia themselves. IS/OS skip RAs may still be visible in a substantial proportion of eyes 6 months after operation.
We believe that becoming familiar with these subtle abnormalities might be useful to explain at least some cases of “unexplained” metamorphopsia occurring in eyes not showing gross OCT abnormalities in the macula after successfully repaired RRD.