In our study, we evaluated the microvascular OCTA parameters of superficial vascular plexus (IVD, FVD, IPD and FPD) and functional outcomes (BCVA) after primary RRD, according to macular involvement, following uncomplicated PPV with postoperative anatomical success.
In the overall analysis, the differences found in the superficial microvascular parameters and the association between BCVA and the OCTA parameters could be explained by the macula-off subgroup, since the majority of patients (23 patients, 71.90%) presented macular detachment and no correlations were found in the macula-on group in the subgroup analysis.
No differences were found between the affected and the fellow eye in the macula-on group, regarding any of the macular vascular parameters, since macular vascular disturbance and ischemia does not occur in eyes classified as macula-on in fundus biomicroscopy. However, Barca and colleagues(20) verified that even in eyes without macular involvement, early reduction of the macular superficial vascular density may be detectable, with a recovery at 6 months of follow-up. In our study, if any microvascular alteration had occurred in the macula-on RRD eyes, this was resolved at 3 months postoperatively, but not in the macula-off group, with worse superficial microvascular parameters and poorer final visual acuity.
In fact, previous studies demonstrated that macular status was associated with visual prognosis.(5, 9, 10, 20) In the macula-off subgroup, the postoperative OCTA quantitative parameters IVD and FVD were significantly decreased when compared with the macula-on subgroup. Higher values of difIVD and difFVD (which means lower IVD and FVD in macula-off eyes comparing with the fellow eyes) and lower values of IVD were correlated with poorer BCVA 3 months after uncomplicated PPV with anatomical reattachment.
Furthermore, the duration of macular detachment is another main preoperative predictor of postoperative VA.(10, 11). We observed that longer duration of macular detachment was significantly correlated with worse BCVA at 3 months. The duration of detachment was itself inversely correlated with several OCTA biomarkers, namely IVD, FDV, IPD and FPD. Christou et al. also observed that macular capillary plexus microcirculation was more vulnerable to changes and tissue destruction caused by RRD with macular involvement in chronic than in recent onset cases.(5) Moreover, the extension of RRD was also significantly correlated with macular microvascular status (IVD and FVD). A longer RRD duration and a larger detachment extension could induce greater ischemic damage and significant microvascular changes. The subretinal fluid (SRF) limits free diffusion of oxygen from the choriocapillaris to the photorreceptor layer, leading to tissue hypoxia and nutrient deprivation. The levels of inflammatory and vascular mediators including prostaglandins, cytokines and endothelin-1 in the SRF are also increased. Muller cell activation and promotion of vasoconstriction are other of the proposed mechanisms for the vascular changes.(5, 20–22) Furthermore, macular vascular flow reduction may be a consequence of an autoregulatory mechanism of reversible vasoconstriction due to hypoxia, which could become sufficiently severe and prolonged following long-duration and extensive retinal detachment, leading to structural vascular changes and capillary dropout.(5, 20)
Regarding other OCTA quantitative parameters, in our study, CVD and CPD were not significantly affected by macular status or correlated with BCVA. Thus, it could indicate the existence of a central vascular region more resistant to the disruptive detachment forces. In fact, a previously described anatomic structure called foveal ring, which consists of the connection point between the three retinal capillary plexuses (and corresponds to the edge of the FAZ) could offer more resistance to a process of hemodynamic instability triggered by the retinal detachment.(23) On the other hand, it emphasizes that the foveola, the thinnest region and responsible for the highest visual acuity, characterized in this study by CVD and CPD, is independent of the vascularization provided by the SCP and, in contrast, fully dependent of the choriocapillary plexus (CCP) perfusion. It would be plausible to conceive that there could be some permanent changes in foveal microvascular parameters as sequels of retinal detachment. Nonetheless, when comparing the affected and fellow eyes, only IPD was significantly decreased in the affected eye. However, and as previously demonstrated by Wang et al, retinal microvasculature tends to recover in some extent over a 12-week follow-up period, after successful surgical repair.(24)
This study has limitations. Firstly, we must point its retrospective nature. Secondly, we investigated the parameters of FAZ, VD and macular perfusion in the SCP and not in the deep nor the choriocapillary plexus due to software limitations that only allowed direct extraction of microvascular parameters in the SCP. Nonetheless, it is hypothesized that in a recent onset disease such as retinal detachment, the SCP is the most affected plexus because it may be the first vascular layer involved due to its greater density in arterioles and in smooth muscle, leading to a stronger and faster contraction with vascular flow, resistance and vessel density changes.(20) Wang et al. and Tsen et al. found similar results, not only comprising the SCP, but also in the deep and choriocapillaris layers.(24, 25) Hong et al. also found that the postoperative subfoveal VD of the CCP was positively correlated with BCVA in macula-off RRD.(26) Thirdly, the sample size was relatively small. Fourthly, we could not disregard the existence of previously described confounding factors including spherical equivalent (although we have excluded patients with spherical equivalent < -6D) and axial length, medication and systemic hypertension, which may influence the microvascular evaluation with OCTA(27, 28) and, possibly, the visual outcome. Moreover, the postoperative follow-up period was relatively short. Our patients were imaged shortly after presentation with a follow-up period of 3 months after surgery, similar to other studies.(5, 20, 24) It would be of great benefit to continue the examination of the patients for a longer period to confirm our results. Lastly, the differences observed in the IPD between the affected and fellow eyes in the overall analysis and among the macula-off group, although statistically significant, were small. This finding should be interpreted concerning its relevance in clinical practice.
In conclusion, we found the decrease of IVD and FVD to be correlated with a worse BCVA exclusively in macula-off eyes, three months after uncomplicated repair surgery with anatomical success. Macular detachment would be the trigger for these vascular abnormalities, which are exacerbated by a longer duration and larger extension of the detachment. These correlations found between BCVA and superficial microvascular changes allow a deeper comprehension of the physiopathology behind vision impairment in macula-off eyes after RRD. Further prospective randomized studies with a larger number of patients and a longer follow-up period should be performed to support our findings and to assess long term visual outcomes.