As described before, the present study had a rigorous design. Before us, few studies focused on the postoperative macular changes in macular-on RRD patients and different tamponade effects due to various intravitreal tamponade choices. We made prudent criteria to avoid potential influence caused by preoperative macular status and surgical options on macular area. Furthermore, we emphasized on the changing value of all OCT/OCTA evaluation indicators during follow-up. Thus, compared to previous studies, we believe that our work could be more reliable in demonstrating different tamponade effects of silicone oil and sterilized air on postoperative fundus change.
It is unethical to randomly choose intravitreal SO or sterilized air as intravitreal tamponade. The criterion of the endotamponade selection was based on surgeon’s comprehensive estimation of intraocular pathological conditions (tear size/tear number/tear location/detachment extent etc.). In the present study, we tried to pick up patients with similar intraocular pathological conditions. The SO group had relatively larger extent of detachment than the Gas group, while the number of retinal tears and symptom duration had no significant intergroup difference (Table
1). More importantly, the macular area was not involved in detachment. Macular vasculature could remain intact in eyes with macula-on RRD [
20]. Thus, we believe that our results could represent the true different tamponade effects between the two intravitreal tamponade materials without being much influenced by other factors. The best time for SO removal is yet to reach a consensus in practice. The removal of SO is recommended to reduce potential SO-related complications such as cataract, glaucoma, and keratopathy. As routine practice for our ophthalmic clinical center, anatomically well-reattached retina based on OCT examination and no sign of progressive PVR after PPV for RRD patients over 3 months indicate SO removal. Thus, the duration of observation in the present study was 12 weeks.
Retinal and choroidal flow density
The macular perfusion changes after RRD surgery have not reached a commitment according to previous researches, which is due to different study designs and observation length. Wu et al. found significantly lower blood flow in both SCP and DCP than fellow eyes after retinal repair [
26]. The surgical operation included vitrectomy and scleral buckling. The follow-up time was relatively longer than our research (3.6 ± 2.4 months, ranging 2–9 months). Wang et al., found significant increase in retinal blood flow in RRD eyes with successful PPV [
22], however, the operation was combined with cataract surgery in their study. Phacoemulsification operation has been demonstrated to increase macular perfusion after surgery for up to 3 months [
28,
29]. Furthermore, these two studies enrolled RRD patients with macular involvement. Detachment of macula before retinal repair could possibly influence macular perfusion even after successful reattachment [
25]. Thus, the finding of differences in the alterations of various retinal blood flow among our macular-on RRD patients is more likely to present the exact fundus vasculature changes after surgery. For retinal blood flow, from 2 weeks to 6 weeks, we found an increasing trend in gas tamponade eyes (Tables
2 and
4). The short-term increase of blood flow might be related to postoperative inflammation [
22]. On the other hand, we found a decrease of blood flow in SO tamponade eyes. More importantly, such opposite changing trend led to significant intergroup difference (Tables
2 and
4). From 6 weeks to 12 weeks, we could still found that SO tamponade led to more blood flow decrease in both SCPFD and DCPFD than Gas tamponade (Table
2). Thus, the present study demonstrated that SO tamponade may result in poorer macular perfusion in both superficial and deep retinal capillary plexus.
For postoperative choroidal status after retinal repair, previous studies used choroidal thickness as an indicator. Akkoyun et al. reported increased subfoveal choroidal thickness (SFCT) at 1 week after retinal repair, which they thought might represent inflammatory reaction [
30]. Karimi et al. reported time-related reduce of SFCT in SO tamponade eyes which may possibly be due to tamponade effect of silicone oil [
18]. However, change of choroidal thickness is not necessarily associated with choroidal vasculature change [
31,
32]. We failed to find any significant result from choroidal thickness comparison during observation. On the other hand, we found significant intergroup difference in parafoveal CCPFD between Gas tamponade and SO tamponade eyes (Table
2). From 2 weeks to 6 weeks, parafoveal CCPFD had more increase in SO tamponade eyes. We suspect the increased of choroidal blood flow in SO group may indicate more severe postoperative choroidal inflammation, which could be related to the relatively greater amount of cryopexy or laser photocoagulation during procedure following SO use. We postulate that choroidal blood flow change could be a more sensitive indicator than choroidal thickness change.
Retinal structural change
In previous studies on retinal structure change after retinal repair, most researchers divided the retinal layer in a relatively general way. In the present study, the retinal layers were strictly segmented into seven layers as introduced in the method section. As components of inner retina, both NFL and GCL + IPL have shown significant intergroup differences in their thicknesses changes. From 2 weeks to 6 weeks, SO tamponade led to more pronounced thickness decrease of these layers than gas tamponade (Tables
3 and
5). Such finding is consistent to the hypothesis of the toxic effect of SO on ganglion cell [
16]. Kamila et al. also reported more pronounced decrease of thickness in GCL-IPL complex after SO tamponade in PPV, compared to gas (C3F8&SF6) tamponade [
16]. As macular was not involved in our RRD patients, our findings may strongly indicate negative tamponade effects of silicone oil on inner retinal structures (NFL&GCL + IPL), which could possibly lead to poorer final visual acuity [
23].
We found relatively more decrease of INL and OPL thicknesses in SO tamponade eyes than in Gas tamponade eyes during our observation (Table
3). Such findings seemed to contradict with results from certain previous studies. Yasin et al. reported thicker central INL and OPL in SO tamponade eyes than in fellow eyes [
17]. Marcel et al. also reported a time related increase of INL-OPL thickness after successful retinal reattachment [
23]. However, their patients all suffered from macular-off detachment. Theoretically, the inflammatory reactions after retinal detachment and reattachment repair may be observed in the pattern of increase in the volume of INL and OPL thickness [
33]. However, in the present study, we found more decrease of these two retinal layers thicknesses in SO tamponade eyes than in Gas tamponade eyes, which led to significant intergroup difference (Table
3). We thought that in the process of structural remodeling of Müller cells after retinal detachment and reattachment, the INL and OPL layer thickness might also be influenced by factors other than postoperative inflammation. SO may have potential negative effects on INL and OPL in the undetached retinal area. Whether our finding indeed revealed variable impacts of different intravitreal tamponades deserve further studies.
Photoreceptor lies in the ONL + IS and OS+RPE layers. The integrity and thickness of IS/OS has been reported to be an important predictor of postoperative VA after RD surgery [
34,
35]. On the other hand, due to ischemia in external layer and neuron cell loss, reduction of ONL thickness after retinal repair has been demonstrated, and maintenance of ONL thickness is also found to be correlated with postoperative VA [
23,
24,
36‐
38]. We found that SO tamponade lead to more decrease in both ONL + IS and OS+RPE thicknesses (Table
3). We hypothesized that compared to gas tamponade, SO tamponade may lead to more thickness loss in ONL, and it might suppress photoreceptor recovery, which could both be related to poorer VA prognosis. Such finding might indicate potential negative impact of SO tamponade on visual prognosis.
During recent years, numerous researches has been performed for the underneath mechanism of Silicone Oil-Related Visual Loss (SORVL), and several pathophysiologic hypotheses have been proposed [
39]. The following factors may all play their roles: photo-toxicity [
40], fat soluble elements from the retina dissolved by SO [
41], lost buffering capacity of the vitreous cavity and presence of intravitreal SO leading to impaired retinal homeostasis [
5,
42,
43]. However, the exact underlying mechanism remains unknown.
Several remarks should be made with respect to the results of this study. On account of tamponade choice and timely SO removal clinical practice in our ophthalmic center, the observation time was relatively short and only comparison between gas and SO tamponade were analyzed. Extended observation period for SO tamponade impact would be necessary in future studies. Due to practical routine of intravitreal tamponade choice in our center, we only compared sterilized air and SO. We obviously lacked fundus vasculature and structure data before surgery as baseline, and we did not take fellow eyes data as control like several previous studies [
16,
17,
22,
24,
26]. Unaffected eyes with asymptomatic feature could have vascular abnormalities in fundus diseases like retinal vein occlusion and primary open-angle glaucoma [
44,
45]. Retinal detachment could also be bilateral in quite a number of patients. Thus, we did not take the fellow eye data of our patients as baseline or control to avoid potential bias. After all, the present study emphasized on the changes of fundus vasculature and structure during follow-up visits. Furthermore, the sample size of our study was relatively small.