Although many clinical trials and studies have been conducted on intravitreal anti-VEGF administration for BVO-ME, most had only a short-term follow-up (less than 3 years) [7]. These studies showed that baseline BCVA, CRT, the integrity of the EZ layer and foveal bulge, and the presence of SRD are predictors of post-treatment visual outcomes. However, to date, limited data exist on long-term (more than 5 years) outcomes. Based on the anti-VEGF therapy followed by a PRN regimen for BVO-ME, we investigated additional useful information to reveal an ideal treatment strategy for BVO-ME from our long-term (average of 64 months follow-up) study. This study demonstrated that baseline BCVA, the integrity of the EZ layer, and the presence of a foveal bulge were significant predictors of post-treatment visual acuity in the long-term, as well as in the short-term, as shown in other studies. In contrast to other studies, this study showed that CRT was not a useful predictor based on long-term observation. Although most studies that have a short-term follow-up showed that the presence of SRD negatively affected visual prognosis, our long-term analysis showed that the presence of SRD at initial presentation did not affect visual prognosis. Still, the presence of recurrent SRD did predict a poor visual prognosis.
To identify associations between visual acuity and clinical features, we classified patients with BVO-ME into 2 groups based on their final BCVA and investigated several parameters for visual prognosis (i.e., Group A [good response to treatment], with a final decimal BCVA of 0.7 or higher; Group B [poor response to treatment] with a final decimal BCVA of 0.6 or lower). Short-term reports have shown a close correlation between 1) final BCVA and baseline BCVA and 2) final BCVA and baseline CRT. In our study, there were significant differences between Groups A and B in the median BCVA at all observation periods [2, 6, 7]. In contrast, there were no significant differences between Groups A and B in the median CRT at any observation timepoint, except at the final visit. Therefore, baseline BCVA is a useful predictor for long-term visual prognosis, as well as short-term prognosis, as previously shown in other studies. In contrast, our study showed that CRT was not a useful predictor for the long term. Interestingly, Group A showed a significant improvement in BCVA in the initial 6 months after treatment start. Moreover, the improved BCVA in Group A was maintained until the final visit. In comparison, Group B did not show the same tendency as Group A. Hasegawa T et al. also reported that an improvement in BCVA was not observed later than 7 months after the initial injection, although there was an improvement during the initial 6 months after treatment start [8]. From the results of Hasegawa’s report and ours, BCVA did not show a remarkable improvement more than 7 months after initial treatment. Therefore, BCVA at 6 months after initial injection is a useful predictor for long-term visual prognosis.
According to the BRAVO and CRUISE studies, improved BCVA and reduced CRT correlated with better visual prognosis in BVO-ME [9–11]. However, in the current study, a reduction of CRT did not correlate with better visual prognosis. Although the BRAVO and CRUISE studies did not analyze the retinal outer segment shape, other reports have studied OCT parameters other than CRT as predictors of post-treatment visual acuity in patients with BVO-ME [7, 12]. For example, Rupak R et al. suggested that the EZ band and foveal bulge must be intact to gain better visual outcomes. Our study also evaluated EZ integrity and the presence of a foveal bulge at 1 month, 6 months after initial injection, and at the final visit. In our study, the ratio that the number of eyes which intact EZ and the presence of a foveal bulge were observed in Group A was significantly higher than that in Group B. We suppose this may be because the EZ band and foveal bulge in Group B had already been damaged at 1 month after the initial injection and never repaired by repeated treatments. Therefore, we believe that severe damage to photoreceptor cells during the ME leads to substantial defects in the outer segments (OS) of the photoreceptor cells, resulting in a lack of the EZ band. Hasegawa T et al. suggested that the foveal bulge seen in OCT images could be related to the morphologic maturation of the photoreceptor OS, which is characterized by an increase in foveal photoreceptor OS density and elongation of foveal photoreceptor. In other words, the lack of a foveal bulge was induced by shortening of the photoreceptor OS length and a decrease in foveal photoreceptor OS density. In addition, even with foveal cystoid spaces in the retina, good visual function may be maintained only if the foveal photoreceptor layer, especially its outer aspect, is preserved. Therefore, similar to Hasegawa’s report, our study showed that integrity of the EZ band and an intact foveal bulge are good predictors of visual function for BVO-ME in the long-term. Moreover, our patients who had severe foveal photoreceptor damage never improved their BCVA in our long-term study. Based on these results, we believe it is very important to protect photoreceptor cells while treating BVO-ME.
Peter A Campochiaro et al. reported that a worsened BCVA in BVO-ME patients was induced by damage to photoreceptors from retinal ischemia and recurrent retinal edema. Photoreceptor damage is more likely to occur with prolonged and/or repeated severe retinal edema. From short-term studies, patients who had SRD at initial presentation tended to have worse visual acuity during the follow-up [13]. Broken retinal capillaries lead to sub-retinal fluid, thickening the retina. Then, Müller cell cones are stretched perpendicularly along the walls of the foveal cystoid spaces. Extended Müller cell cones break the external limiting membrane (ELM) barrier, resulting in SRD [14]. However, even though the presence of SRD is believed to be the most important factor for evaluating visual prognosis in patients with BVO-ME, our long-term study showed that SRD at initial presentation did not affect final visual acuity. Nonetheless, the presence of a higher recurrent SRD ratio led to poor visual acuity (Table 3). According to previous reports, VA and CRT can be improved by anti-VEGF treatment in patients with BVO-ME with or without SRD [13, 15]. In addition, a more marked improvement of macular structure was achieved in patients with SRD than in those without SRD. These findings may be explained by the strong association of inflammatory factors and extensive morphological changes with the occurrence and/or recurrence of SRD, thus patients with SRD have better improvement of macular structure by anti-VEGF treatment [13]. Based on previous reports and the current study, we suggest that if SRD is observed only at the first presentation, it does not necessarily predict poor visual prognosis because anti-VEGF treatment can alleviate damage to foveal photoreceptors in the outer segment by restoring the ELM barrier and improving macular structure and function [15]. In comparison, the presence of recurrent SRD causes further damage to the retina, resulting in poor visual outcomes. Therefore, it is important to introduce anti-VEGF treatment at appropriate timing, with attention to the presence of recurrent SRD, to better optimize visual outcomes.
Unlike in the case of AMD, there is no standard regimen for RVO-ME with anti-VEGF agents. In the BRAVO trial, patients received monthly intravitreal ranibizumab (IVR) in the first 6 months, and additional injections during the subsequent 6 months if the patient met the prespecified criteria (6 + PRN regimen). In contrast, the BRIGHTER trial confirmed the efficacy of a less frequent treatment regimen (3 + PRN regimen), where patients received monthly IVR until the VA was stable for 3 consecutive months, and if VA did not change after the last monthly treatment, the next re-treatment was warranted only when VA decreased and if the decrease was due to disease activity in the opinion of the investigator. Considering the relatively good final-visit BCVA in this study (0.097 log MAR unit, which is equivalent to 80 ETDRS letters), we believe the BCVA at the final visit here was comparable to that in the BRIGHTER study (75 ETDRS letters) [16]. Moreover, our 1 + PRN regimen over the course of 2 years maintained the BCVA with fewer IVR injections compared with the PRN regimen over 2 years of IVR injections used in the BRIGHTER study (7.1 ± 2.41 vs 11.4 ± 5.81 injections, respectively). Therefore, 1 + PRN regimen of anti-VEGF injections for BVO-ME could lead to an improved BCVA and be useful in clinical practice.
Similar to the RETAIN study, which reported that 50% of patients with BRVO were treated by anti-VEGF injections for over 4 years, our study also demonstrated that many patients receive long-term anti-VEGF injections (64.38 ± 15.07 [range, 38–100] months) to maintain or improve their visual function. Therefore, long-term observation with proper treatment is essential for better visual outcomes.
There were some limitations in this study. First, it was a retrospective study design with no control group and small sample size. Second, the choice of anti-VEGF drug, including ranibizumab and/or aflibercept, was decided by the treating physicians. The effectiveness of these 2 drugs was not investigated separately. Third, patients who had less than three years of follow-up were excluded from this study. This may have introduced a selection bias, if the excluded patients were good responders to anti-VEGF treatment.
In conclusion, this study demonstrated that the integrity of the EZ band and an intact foveal bulge (signifying intact photoreceptor cells) were significant predictors of post-treatment visual acuity in the long-term and short-term. In comparison, we found that recurrent SRD led to poor visual acuity in this long-term study, even if patients with BVO-ME had a good BCVA in the short-term. Therefore, this study showed that recurrent SRD is an important indicator for poor visual prognosis during long-term observation.