In this study, we performed a quantitative assessment of macular vascular density using OCTA and compared the macular blood perfusion before and after phacoemulsification cataract surgery in Chinese normal eyes. We limited the patient's axial length and age to a small range, because these factors may affect the fundus blood flow . Of note, we found that blood flow parameters in the macula area increased gradually and stabilized in about one week after surgery. FAZ related parameters are stable before and after surgery. Main parameters of phacoemulsification surgery have no statistically significant correlations with changes of macular hemodynamics.
The development of phacoemulsification technology has made it one of the most popular techniques in treating cataracts. Surgeons use maximum vacuum to reduce direct damage by the power of phacoemulsification, but it brings the effect of high perfusion pressure at the same time. Previous reports have reported that the instability of the fluidics system during cataract surgery results in a longer operation time and an increase in CDE, which in turn will lead to longer recovery time and even poor visual function in postoperative patients [1–2]. So we wonder whether the fluctuation of intraocular perfusion pressure during phacoemulsification affect fundus microcirculation and then affect the patient's postoperative vision. A few studies have reported the effects of cataract surgery on ocular hemodynamics[10–12]. However, there is a shortage of research on this issue and there is a lack of quantitative study and large number of cases. The emergence of OCTA provides us with new ideas to explore.
The main methods of studying ocular blood flow reported in the literature can be divided into non-invasive and invasive techniques. Invasive techniques primarily involve scanning laser ophthalmoscopic angiography with fluorescein and/or indocyanine green (ICG) dye. These two methods often result in an allergic reaction due to the intravenous administration of dye before examination, and are relatively expensive and time consuming.. Many non-invasive methods based on Doppler technology for detecting ocular blood flow, such as color Doppler imaging (CDI), laser Doppler velocimetry (LDV), laser Doppler flowmetry (LDF). However, their ability to visualize retinal blood vessels, especially retinal microvessels, is limited. Moreover, methods like laser speckle technique and blue field entoptic technique have a large degree of dependence on the subject's cooperation and the study of the fundus structure are limited [3–4]. With the development of OCTA and the gradual application in ophthalmology, non-invasive and quantitative research of fundus blood vessels has become possible[6–8]. It use the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm through the intrinsic motion contrast provided by the flowing erythrocytes, making it possible to noninvasively obtain three-dimensional mapping of the retina and choroidal microvasculature[15, 16]. Good reproducibility and repeatability of OCTA on vascular and FAZ measurements have already been demonstrated[17–18]. So our study used this quantitative method to figure out whether transient hyperperfusion in cataract surgery affects fundus blood flow.
Many literatures have reported the effects of phacoemulsification cataract surgery with intraocular lens implantation on ocular hemodynamics by using various techniques[19–22]. EJR Hilton et al. found that small incision cataract surgery led to an 8.3% postoperative increase in pulsatile ocular blood flow (POBF) after one month following surgery, which was comparable with our present results . However, Spraul CW et al. described a post-operative decrease in POBF and pulse amplitude at 3 days that was not apparent 12 months later , Rainer G. et al reported no change in fundus pulse amplitude, or blood-flow velocities and resistance of the retrobulbar vessels up to 1 month following cataract surgery . And Adam Turk et al. indicated that there were no significant differences in IOP, POBF, and ocular pulse amplitude (OPA) between one week and three weeks after cataract surgery in a study of 52 eyes of 26 subjects. Nevertheless, due to the different equipment used as well as the diversity of the group properties, the conclusions of those previous studies were not highly comparable with our present results.
Furthermore, research methods mentioned above focused more on large vessels than the microvasculature in eye, which is a limitation to show pathophysiologic changes in macular vessels . And the pulsatile component we used to measured is thought to be primarily choroidal in origin which could hardly describe the retinal, especially the macular vessels in a precise way. However, OCTA provides segmented image of the macular vessels and quantitatively measure blood flow at a given location. Siqing Yu et al. used OCTA to study 13 cataract eyes and observed that there was a increase of either perfusion or vessel density on superficial capillary plexus (SCP) and deep capillary plexus (DCP) in a 3 mm × 3 mm en face image one week after surgery, which is consistent with our results. Siqing Yu et al. attributed this increase as the result of the different refractive interstitial conditions before and after surgery. But they did not measure patients’ ocular blood flow status immediately after the surgical intervention was performed, which ignoring the impact of cataract surgery on the macular hemodynamics. Zhennan Zhao et al. studied 32 cases of uncomplicated phacoemulsification surgeries by using OCTA. Significant increases in macular vessel density and macular thickness were found in one month and three months postoperatively. This is basically consistent with the conclusions of our larger sample study. Previous studies have pointed out that fundus perfusion will eventually improve due to the IOP-lowering effect of cataract surgery, which is believed to result from the widening of the anterior chamber[26–29] and vasodilator effect of inflammatory factors[30, 31]. The interpretation of these studies is in support of our findings. Moreover, most of the subjects had earlier cataracts (LOCS scale,median: N3, C4, P3) in current study in order to ensure the imaging quality of larger en face images (6mm × 6 mm), so the effect of lens opacities were diminished.
Previous clinical studies of FAZ have used techniques such as fluorescein fundus angiography (FFA), fundus photography (FP) and adaptive optics scanning laser ophthalmoscopy (AOSLO), all of which have limitations on clinical application due to their invasiveness, complex equipment and long scanning time[32–35]. Some clinical studies using OCTA to analyze FAZ[36–40] are mainly focused on diabetic retinopathy(DR) have shown a decrease in total retinal blood flow associated with an increase in FAZ area with increasing age[41, 42]. Our inclusion criteria have avoided the interference of age factors on the results. Meanwhile, studies[37, 43] of DR patients have showed that the size of FAZ was negatively correlated with both the macular vascular density and BCVA. Therefore, FAZ parameters may detect the impairments of macular micro-vessels and visual function to some extent. In our study, the FAZ area of subjects after cataract surgery increased first and then decreased, while the differences were not significant (P > 0.05). This difference may be due to participants in our study have no systemic vascular disease. The postoperative microcirculation change was only transient and mild, with no qualitative vascular changes. Our result is consistent with the findings of Siqing Yu et al. that there were no significant differences in FAZ area and perimeter between preoperative measurements and one week after cataract surgery. However, unlike our findings, Zhennan Zhao et al found a decrease in the foveal avascular zone after cataract surgery. We analyzed this difference may be contributed to the inconsistency in the axial length of enrolled patients included in the two studies.
The effects of various surgical parameters on ocular structures have been of concern and efforts have been made to evaluate the same[44, 45]. However,there is a shortage of literature on the effect of different flow parameters on the posterior segment. Previous studies demonstrated that phacoemulsification ultrasound energy can induce the production of some cytokines, which in turn affects ocular hemodynamics. This prompts us to explore the correlations between surgical parameters and changes in ocular blood flow. A 6mm × 6 mm OCTA image were used in this study to quantitatively calculate the rate of change of macular vascular density before and after surgery. In our study, no statistically significant correlations were observed between the two parameters (EPT and CDE) and rate of change in both superficial and deep macular vascular densities. It suggests that the main parameters of phacoemulsification surgery may not be the key factors affecting macular hemodynamics. However, the LOCS nuclear opalescence score of our subjects between 2 + and 3+, which may result in a very small fluctuation of surgical parameter and reduce its influence.
The main limitation of this study is the lack of research on patients with more severe cataracts. However, this study is the basis for exploring the effects of phacoemulsification on macular hemodynamics in different populations in the future. Furthermore, studies in the future are needed to focus on abnormal eyes, especially patients who with high myopia, glaucoma and systemic vascular disease. This will give clinicians more reference for practice. For example, a highly myopic patients who have long eyes, weak eyeball wall and liquefying vitreum, will have greater intraoperative IOP fluctuations. Comparison of ocular vasculature changes between long eyes and normal eyes before and after surgery can guide clinicians to further optimize surgical parameters and clinical medication. This study can also be a basis for further studies of fundus hemodynamic changes after vacuum application in femtosecond laser-assisted cataract surgery.