Choroidal structural changes following vitrectomy performed with phacoemulsification in unilateral idiopathic epiretinal membrane

The CVI represents the proportion of the lumens of choroidal vasculature in the choroid and is considered a marker of choroid vascular health [14, 15] as well as a relatively stable and consistent indicator of choroidal disease progression. It has been frequently used in evaluating the choroidal vascular structure changes in various ocular diseases such as uveitis or diabetic retinopathy [12, 16, 17].

It has been reported that the CVI and/or CT increased after cataract surgery, which lasted at least 3 months [17], whereas the CVI and/or CT decreased after PPV. Thus, there is a possibility that phacoemulsification and vitrectomy have opposite effects on the choroidal vessels. Understanding the changes in the choroid after combined vitrectomy with phacoemulsification can help predict the visual prognosis of ERM patients with cataract after the combined operations. Nevertheless, the influence of combined surgeries on choroidal vasculature is not well understood in this population, so this study aimed to investigate the effects of combined operations on the choroidal vasculature.

The changes in CT and CVI were measured before and after phacovitrectomy to explore the choroidal vasculature changes in IERM and the influence of surgery, showing that the CVI of the IERM patients increased significantly within 3 months after phacovitrectomy surgery, which suggests choroidal vessels dilatation. At the same time, the CT also increased significantly in some areas of the macula, in line with CT changes after cataract surgery. Prolonged inflammatory reactions have been described after cataract surgery [18] with proinflammatory cytokines expressed in the choroid following cataract surgery, and there is evidence of upregulation of IL-1β and CCL2 gene and protein expression in the choroid [19]. The vitrectomy also causes inflammation as part of the healing process, with increased cytokines such as TGF-β1, IL-8, and IL-6 in the aqueous humor [20]. In addition, the reduced IOP is likely to cause increased CT in the early period following phacoemulsification performed with or without vitrectomy due to increased ocular perfusion pressure [21, 22]. The present study demonstrated that the CT/CVI increased in the early postoperative period, which is similar to that reported in ERM and MH patients undergoing vitrectomy [21, 23]. Therefore, the upregulation of proinflammatory cytokines and the decreased IOP after surgery might cause an increased CVI/CT after combined vitrectomy. The decreased IOP might increase the CVI/CT in the early postoperative period, which lasts at least 1 week postoperatively, and the inflammation-induced increase in CVI/CT might last at least 3 months.

Moreover, recurrent ERM is also a process of fibrocellular proliferation caused by excessive collagen production by hyalocytes, RPE cells, or retinal glial cells, which might remain after surgery or migrate to the surface of the retina because of surgical trauma. Though the cause of ERM recurrence is unclear, greater surgical trauma and subsequent postoperative inflammation might increase the recurrence rate [24]. Whether the increased surgical trauma and inflammatory response caused by combined surgery increase the recurrence rate compared with non-combined surgery may be worthy of further studies.

The pathological mechanism of IERM has not been fully elucidated, but posterior vitreous detachment (PVD) is considered an important pathogenic factor. Anteroposterior (AP) traction promotes the expression of growth factors, including vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) in the retina [25, 26]. In our study, the 26 patients with unilateral IERM without VMT lacked mechanical AP traction, but the IERM eyes did not have a greater CT than the fellow eyes. Although the average CT of the macula in ERM eyes was not significantly different from that of the fellow eyes, the subfoveal and nasal CT values of ERM eyes were respectively thinner than that of fellow eyes at baseline. Interestingly, CVI was lower at baseline in the ERM eyes than in the fellow eyes, which might imply the possible involvement of abnormal choroidal vessels in the pathogenesis of IERM, especially unilateral IERM. Kang et al. found that choroidal thickness was greater in IERM eyes with than without VMT, suggesting that VMT could lead to choroid thickening, but they did not compare the results with fellow eyes [27]. Other studies did not observe any difference in the CT between the fellow eyes [28] or a significantly higher CT in IERM eyes than in fellow eyes [29]. However, the presence or absence of VMT was not described in these studies, and not all patients were unilateral, which may be the reason for the inconsistency in results. Therefore, further larger studies are needed with more precise grouping.

It was reported that ERM could influence the choroid microvasculature through ERM-associated traction [30]. In this study, CMT decreased significantly postoperatively compared with baseline 3 months after ERM-ILM removal. The release of mechanical stretching mainly led to a decrease in thickness of retina. As mentioned above, CT increased after surgery, whereas CT subsequently decreased gradually within 3 months postoperatively, which might be due to the combined effect of reduced mechanical stretching and decreased level of VEGF and inflammatory cytokines as time went on after surgery.

This study has some limitations. First, the relatively small sample size, but the patients had a consistent diagnosis, homogeneous ethnicity, and underwent the same surgery method, thereby reducing some confounding effects. A second limitation is the short period of follow-up of 3 months, so a long-term follow-up should be conducted with a larger sample.

In conclusion, the present study revealed increased CVI and thickened CT following phacoemulsification performed with vitrectomy in eyes with unilateral idiopathic epiretinal membrane without VMT, suggesting that the choroidal vessels dilate due to postoperative inflammation. However, whether the increased postoperative inflammation could be a potential risk of recurrence requires further investigation. Future studies should involve a long-term follow-up to determine how long the increase in CVI/CT and the possible latent postoperative inflammation following phacoemulsification will last after surgery, as well as the possible effect on visual prognosis and ERM recurrence in this population.

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