Characteristics of macular microvasculature before and after idiopathic macular hole surgery

INTRODUCTION

An idiopathic macular hole (MH), caused by tangential traction, can be successfully closed by pars plana vitrectomy with gas-fluid exchange. The anatomic and functional outcomes were further improved by the advent of peeling of the internal limiting membrane (ILM). However,the postoperative visual acuity (VA) is sometimes poor despite successful anatomic closure. Long-term restoration of the microstructure and function of the fovea has been evaluated following surgery for idiopathic MH. Previous studies in eyes with MH have focused mainly on disruption of the outer retina, including the external limiting membrane (ELM), the ellipsoid zone (EZ), and the photoreceptors with respect to the visual prognosis.

Recently, researchers demonstrated an association of disorganization of the retinal inner layers (DRIL) with VA in various retinal diseases. The presence of vitreous cortex,proliferative glial tissue, and retinal hydration has been suggested as factors in the formation of macular holes in histologic studiesand possibly contribute to DRIL. DRIL indicates specific anatomic damage to the structures in the retinal layers that transmit visual data and also a poor inner retinal circulation.

对于公路工程施工所使用的机械设备，应该确保机械设备不是老旧设备，若经常出现故障将直接影响施工进度，应该在项目资金可支配的情况下，优先考虑购买或者租赁技术先进的机械设备，确保项目的施工效果和施工进度能够满足预期的要求。

With the development of imaging technology, optical coherence tomography angiography (OCTA) provides highresolution, depth-resolved images for evaluation of the retinal capillary plexuses in eyes with MH in a noninvasive and dye-free manner. In our previous work, we used a commercially available OCTA device with custom-built imaging software and concluded that disorders in the inner retinal vessels corresponded to disruption of the outer retinal layers and VA in the setting of dysfunctional vasculature.The recovery of the retinal microvasculature in patients with a surgically closed MH remains to be elucidated. Meanwhile,limited information is available regarding quantitative evaluation of the preoperative status of the retinal microvasculature in eyes with MH. Accurate OCTA measurements should correct for ocular magnification and require information on axial length.Until now, no study has accurately quantified the changes that occur in the vasculature of the macula in eyes with MH after surgical treatment or the relationship between preoperative vascular parameters and the postoperative VA.The aims of this retrospective study were to characterize macular microvasculature in the superficial and deep retinal layers following surgery in patients with idiopathic MH using OCTA and to investigate the association of preoperative microvascular parameters in the inner retina with postoperative best-corrected visual acuity (BCVA) and healing.

SUBJECTS AND METHODS

This study was approved by the Ethics Committee at Wenzhou Medical University and complied with the tenets of the Declaration of Helsinki. Informed consent was obtained from all patients.

Independent-test and Mann-Whitneytest were used to compare continuous variables between the groups. Repeated-measures analysis of variance was used to evaluate differences in the chronologic data. Post multiple comparisons were evaluated using the Bonferroni test. The Pearson correlation test was used to determine the associations between preoperative vascular parameters and postoperative BCVA. The associations between preoperative vascular parameters and postoperative healing stage were evaluated using the Spearman correlation test. All data are expressed as the means±standard deviations and analyzed with SPSS version 22.0 software (IBM Corp., Armonk, NY, USA).logMAR values of 2.0 and 3.0 were assigned for counting fingers and hand motion vision, respectively.<0.05 indicated statistical significance.

The AngioVue version 2017.1.0.155 software was used. The macular region was imaged using a central 3×3 mmarea. Low-quality OCTA images with a scan quality <5/10, severe artifacts attributable to poor fixation, or failure of automatic layer segmentation were excluded. The area and perimeter of the foveal avascular zone (FAZ) were determined by the software embedded in the instrument. The vessel density (VD) was calculated as the percentage of pixels with a flow signal greater than the threshold value and automatically measured using custom-built imaging software implemented in MATLAB (Mathworks,Natick, MA, USA). The mean brightness of the FAZ was taken as the threshold for the retinal vessels. Parafoveal and perifoveal VDs were calculated in the regions of the radius between 0.5 and 0.875 mm and between 0.875 and 1.25 mm,respectively, from the foveal center (Figure 1A, 1B). To reduce the effects of decentration of the FAZ and the artifacts at the edge of the scan, a circular area with a diameter of 2.5 mm was used instead of the entire 3×3-mmarea.

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layer, and outer plexiform layer could not be identified. Two independent observers interpreted the OCTA and OCT images.The observers reached a consensus in all cases.To eliminate the effect of magnification, the images obtained by OCTA and OCT were corrected by Bennett’s formula using the axial length. The relationship between the OCT image measurements and the actual scan diameter was expressed by the formula t=p×q×s, where t is the actual axial length, p is the magnification factor determined by the camera of the OCT imaging system, q is the magnification factor in relation to the eye, and s is the original measurement obtained from the OCT image. The correction factor q was determined using q=0.01306×(AL–1.82).

Preoperative minimum diameter of the MH was measured in the OCT images. The postoperative healing stage,,restoration of the photoreceptor layer, was graded from 1 to 3. Grade 1 was assigned when the EZ and ELM were disrupted, grade 2 when the EZ was disrupted but the ELM was restored, and grade 3 when both the ELM and EZ were restored. DRIL was defined as the horizontal extent within the central 2000 µm for which any boundaries between the ganglion cell-inner plexiform layer complex, inner nuclear

英国人洛克曾说过“在缺乏教养的人身上，勇敢就会成为粗暴，学识就会成为迂腐，机制就会成为逗趣，质朴就会成为粗鲁，温厚就会成为谄媚。”若这种现象发生在承载着实现中华民族伟大复兴梦希望的大学生身上，恐怕是所有人都不想看到的。而事实却是部分大学生责任感与使命感缺乏、浮躁与迷惘俱在、审美价值观扭曲，这是不容否认的现象。因此，面对当前的大学生审美价值观现状，作为审美教育的影视艺术教育理应成为改变这一现状的中坚力量，积极引导大学生树立正确的审美价值观。与其他的价值观教育途径相比，影视艺术教育会通过左右大学生的审美价值观进而在潜移默化中影响大学生整个价值观念体系的形成。

All procedures were performed by a single surgeon. Standard 3-port pars plana vitrectomy was performed using 23-gauge instruments. Cataract surgery was performed on all 20 phakic eyes. A 31-year-old patient underwent cataract surgery for congenital cataract. A concentration of 0.025% indocyanine green (ICG) was injected into the vitreous cavity and washed out no later than 3 seconds by 23-gauge cutter. Then the ILM was peeled by carefully grasping with forceps without retinal damage to about 4-disc diameters centered on the macula. All patients performed fluid‐air exchange with air, and the sclerotomies were sutured.Patients were instructed to remain in a prone position for 3-5d postoperatively.F: Female; M: Male; OS: Left eye; OD: Right eye; BCVA: Best-corrected visual acuity.

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The medical records of patients who had undergone successful MH closure by vitrectomy and ILM peeling in the Fundus Department at the Eye Hospital, Wenzhou Medical University, from June 2018 to May 2020 were reviewed. Each patient underwent a complete ophthalmic examination, including slit-lamp examination, intraocular pressure measurement, fundoscopy, preoperative axial length measurement, OCT (Spectralis; Heidelberg Engineering,Heidelberg, Germany), and OCTA (AngioVue; Optovue,Inc., Fremont, CA, USA). The slit-lamp, fundoscopy, OCT,and OCTA examinations were performed before surgery and 2wk, 1, and 3mo after surgery. The inclusion criterion was a Gass stage 2-3 idiopathic full-thickness MH confirmed on OCT. Eyes with macular disease, such as age-related macular degeneration, epimacular membrane, myopic choroidal neovascularization, a spherical equivalent refractive error>±6.0 diopters, significant cataract (LOCS scale higher than N2, C1, P2)or macular edema after surgery, glaucoma,other marked complications, or a history of intraocular surgery were excluded. Chronic macular holes (defined by visual symptoms of greater than 1y), heavy smokers, or patients with systemic disease, such as diabetes, hypertension were also excluded. The patients were divided into groups according to whether or not their 3-month postoperative BCVA was <20/32 or ≥20/32.

RESULTS

Fortythree eyes of 43 patients with an MH underwent vitrectomy with ILM peeling between June 2018 and May 2020. Twentythree eyes were excluded (8 for high myopia, 4 for severe cataract that prevented acquisition of high-quality OCTA images, 4 for age-related macular degeneration, 2 for diabetic retinopathy, 2 for myopic choroidal neovascularization, 2 for OCTA images of poor quality, and 1 loss in postoperative follow-up), leaving 20 eyes of 20 patients for inclusion (Table 1).

The patients mean age was 59.1±10.1y. Fourteen patients were female (70%) and 6 (30%) were male. The mean preoperative axial length was 23.9±1.1 (range 21.77-25.52) mm. Before surgery, the mean minimum diameter of the hole was 462.9±208.3 (range 206-871) µm.

The logMAR BCVA improved from 0.98±0.59 (range 0.22-2.00,Snellen equivalent 20/200) preoperatively to 0.93±0.64 (range 0.30-3.00, Snellen 20/160) at 2wk, 0.47±0.25 (range 0.15-1.00, Snellen 20/63) at 1mo, and 0.30±0.25 (range 0-1.00,Snellen 20/40) at 3mo postoperatively. Ten patients (50%) had evidence of different degrees of DRⅠL on OCT images during the post-surgery recovery of MHs (Figure 1C, 1D).

统计分析结果表明(表3)：不同施肥处理间新竹株数、胸径以及产量均无明显差异；不同密度条件下，新竹株数与产量同样没有产生明显差异，而对于平均胸径，则低密度林分明显高于高密度林分(P=0.041<0.05)。

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There were significant changes in all vascular parameters after MH surgery (Table 3). The changes in parafoveal and perifoveal VD in both layers are shown in Figures 2 and 3.Before vitrectomy, the mean parafoveal and perifoveal VD values were 47.4%±2.7% and 47.2%±0.03%, respectively, in the superficial layer and 49.2%±0.05% and 47.7%±0.04%,respectively, in the deep layer. A significant reduction in VD was observed 2wk after surgery. Furthermore, there was evidence of recovery of the macular microvasculature in the superficial plexus at 1 and 3mo postoperatively. In the deep plexus, there was no difference between the preoperative VD and the VD at 1mo postoperatively in either region. The mean perifoveal VD at 3mo postoperatively was even greater than that before surgery.

The mean preoperative area and perimeter of the FAZ were 0.43 mmand 2.8 mm, respectively (Figure 2A, 2D). Significant reductions in the mean values for the FAZ parameters were observed during the follow-up period (Table 3 and Figure 2).

There was a correlation between decreased preoperative parafoveal and perifoveal VD in the deep layer and worse 3-month VA(Pearson’s=-0.667 and -0.619, respectively; Table 4, Figure 4A, 4C). A larger FAZ perimeter (Spearman’s=-0.524) and decreased perifoveal VD preoperatively in the deep layer(Pearson’s=0.486) was associated with lower healing stage of photoreceptor layers (Figure 4B, 4D). There was no correlation between FAZ, superficial vasculature parameters and VA at 3mo after surgery. No correlation was found between preoperative superficial VDs and postoperative healing stage.

DISCUSSION

Several studies have investigated the preoperative configuration of MH using OCT and searched for predictors of the visual outcome after surgery. To the best of our knowledge,postoperative visual recovery has not been evaluated as a predictive parameter by OCTA in eyes with MH. We demonstrated that the preoperative macular microvasculature was denser in eyes with MH that had better VA after surgery,especially in the deep capillaries. Moreover, correlation analysis revealed that a decrease from the preoperative deep capillary VD was strongly correlated with worse postoperative VA. We speculate that this could be attributed to several possible mechanisms. Tornambeproposed the“hydration theory”, whereby during formation of an MH, after the posterior hyaloid has created a retinal defect, vitreous fluid first passes through the inner retina and disrupts homeostasis.Liquid vitreous fluid then accumulates, the MH appears to enlarge, and the inner retinal tissue become swollen, especially in the outer plexiform layer. DRⅠL was recently identified to be a sign of poor inner retinal circulation, indicating disruption of the pathways that transmit visual information from the photoreceptors to the ganglion cells and seemed to be a correlated predictive biomarker for VA in various diseases. We observed a similar phenomenon in a previous study. Given their special watershed-like position, the deep capillaries may be more prone to ischemia and contribute to disruption of the photoreceptor layer and then visual function. The suggested pathophysiologic changes within the inner retinal vasculature,which are supported by histopathologic and imaging studies,collectively may have accounted for the decreased deep blood flow seen in our study.

There were significant differences in preoperative VA, perimeter of the FAZ, and parafoveal and perifoveal VD in the deep plexus between the group with a 3-month BCVA<20/32 and the group with the 3-month BCVA≥20/32 (Table 2). Ⅰn the group with the 3‐month BCVA<20/32, the preoperative VA was significantly worse,and the perimeter of the FAZ was larger. In the deep capillary layer, the VDs in both regions was smaller. The minimum diameter of the hole and the area of the FAZ were larger, albeit not significantly so. No significant differences were found in patient age, preoperative stage, axial length, or VD in either region of the superficial layer.

We quantitively demonstrated recovery of the macular vasculature with magnification correction before and after surgical intervention in eyes with MH. Scupolareported significant improvement in retinal function at 3mo after closure of an MH that was confirmed to be maintained at 6 and 12mo by focal electroretinography. Therefore, we compared the microvascular networks in eyes with MH before, 2wk,1, and 3mo postoperatively. Significant reductions in FAZ parameters were observed 2wk postoperatively, suggesting a movement of foveal tissue toward the central fovea and a centripetal movement when the MH is closed. However, the 2‐week postoperative VDs decreased significantly, and the VA improved only slightly, indicating prompt structural recovery but delayed functional repair. Kimand Demirelreported that the postoperative VD in eyes with a closed MH,particularly in the deep plexus, was lower than that in either fellow eyes or healthy eyes. In the present study, most VD values recovered only to the preoperative status, indicating a lack of functional vascular integrity after surgery. The disrupted microvasculature may impede the dynamic healing process and provide another explanation for the unsatisfactory visual gain after surgery despite successful anatomic closure of the MH.

Correlational analysis revealed a moderate correlation of a decreased deep perifoveal VD and an increased FAZ perimeter with poor healing. The ischemia in inner retinal vasculature is considered to contribute to the disorganization of the outer retina and to lead to poor restoration of the microstructure of the fovea.

This study has several limitations. The first is its retrospective design and relatively small sample size. The second relates to the fact that eyes with MH tend to have poorer stable fixation before surgical closure, leading to exclusion of OCTA images with poor quality upon visual inspection.In conclusion, OCTA analysis before and after surgery in eyes with MH demonstrated the preoperative macular microvasculature and suggests that the status of the deep plexus could predict the postoperative visual outcome.Quantification of the retinal vasculature postoperatively would provide an explanation for the limited visual recovery after surgical closure of MH.

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手写苗文文字样本经过扫描仪进入计算机后，因纸张的厚度、光洁度和取样设备质量的不稳定都会造成录入后的数字图像文字畸变，形成粘连、笔画中断和图像噪点等干扰，所以在进行文字识别之前，务必要对带有噪声的文字图像进行处理。图像预处理方法有许多经验成果〔9-10〕，其大体步骤包括文字图像大小归一化、灰度化、二值化、规范化等等。

Supported by the National Natural Science Foundation of China (No.81900910; No.81700884); Natural Science Foundation of Zhejiang Province (No.LQ19H120003;No.LGF21H120005); Key Project Jointly Constructed by Zhejiang Pronvince and Ministry (No.WKJ-ZJ-2037); Basic Scientific Research Project of Wenzhou (No.Y20210194).

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