With the increase in educational pressure and limited time outdoors, myopia has become the most common vision problem (Morgan et al., 2018). Recent epidemiological studies indicated a prevalence of myopia as high as 80%–90% in young adults in East Asia (Foster and Jiang, 2014; Wu et al., 2016). It is estimated that, in 2050, half of the world’s population will be affected with myopia and 10% of people will be at a relevant risk of becoming blind as a result of high myopia (Holden et al., 2016; Hopf and Pfeiffer, 2017). With the elongation of the eyeball that occurs with the progression of myopia, the retinal microvascular decrease was observed in the myopia subjects (Yang et al., 2016; Al-Sheikh et al., 2017; Li et al., 2017).

Since the introduction of the Implantable Collamer Lens (ICL; Staar Surgical, Nidau, Switzerland) in 1993, refractive surgery has entered a new era of myopia treatment (Assetto et al., 1996). Because it significantly increased best-corrected visual acuity (BCVA) while reducing caused higher-order aberrations and improving postoperative contrast sensitivity (Wang and Zhou, 2016), the ICL is most frequently used to correct high and extreme myopia. In addition, the ICL performs superbly in the treatment of low to moderate myopia (Kamiya et al., 2012; Dougherty and Priver, 2017; Kamiya et al., 2018).

However, multiple studies revealed that intraocular refractive surgery, such as cataract surgery, may lead to early retinal ischemia, hypoxia, or even retinal vasculitis (Alnawaiseh et al., 2018; Kim et al., 2018; Pilotto et al., 2019; Liu J et al., 2021). Retinal complications would cause a potential or substantial threat to patients’ vision. So, it is vital to monitor retinal microvascular alteration after intraocular refractive surgery. ICL implantation is also a kind of intraocular refractive surgery. However, it is still unknown whether the ICL implantation surgery will affect the retinal microvasculature of myopic eyes.

Optical coherence tomography angiography (OCTA) is a new, non-invasive imaging technique with wide application potential for retinal vascular disease (de Carlo et al., 2015; Gao et al., 2016; Wylegala, 2018). In 2006, Optical Coherence Angiography was first performed to visualize the vasculature in the human eyes (Makita et al., 2006). OCTA can produce high-resolution, three-dimensional images and measure the microvascular network in different layers of the retina structure without the use of contrast agents (Gao et al., 2016; Zhang Q et al., 2016). This study aimed to use OCTA to uncover potential retinal capillary network alterations induced by ICL implantation surgery.

The demographics of the enrolled subjects are summarized in Table 1. The mean patient age at the time of surgery was 27.0 ± 3.8 years (ranging from 21 to 36 years). The preoperative manifest refraction spherical equivalent (MRSE) was −8.50 ± 2.68 D (ranging from −3.50 D to −13.88 D). The preoperative manifest sphere was −7.95 ± −2.57 D (ranging from −3.00 D to −13.75 D). The preoperative manifest refractive cylinder was −1.16 ± 0.92 D (ranging from 0.00 to −3.25 D). The IOP was 14.60 ± 2.71 mmHg. AL was 26.63 ± 1.06 mm (ranging from 24.87 to 29.50 mm). WTW was 11.90 ± 0.31 mm (ranging from 11.3 mm to 12.7 mm). ACD was 3.26 ± 0.25 mm (ranging from 2.92 mm to 3.80 mm).

All surgical procedures were uneventful, and no postoperative complications, such as cataract formation, pigment dispersion syndrome, pupillary block, or axis rotation, were seen throughout the observation period. Visual acuity improved for all patients on the first day after surgery. Three months postoperatively, 2% of eyes lost one line of vision and 98% of eyes maintained or gained BCVA (Figure 3A). The efficacy index was 1.11 ± 0.24 (preoperative BCVA: 0.01 ± 0.06 logMAR and postoperative UCVA: −0.02 ± 0.06 logMAR, p < 0.05; Figure 3B). The mean preoperative IOP and postoperative IOP (14.6 ± 2.7 versus 15.2 ± 3.2, p > 0.05; Figure 3C) were not significantly different. At 3 months postoperatively, 90% and 100% were within ±0.5 and 1.0 D of the attempted correction, respectively (Figure 3D). The time course changes in the manifest refraction were shown in Figure 3E. Changes in the manifest refraction from 1 day to 3 months were 0.02 ± 0.68 D. Three months postoperatively, the vault was 0.64 ± 0.20 mm.

Preoperative versus postoperative retinal microvascular density for myopia patients, with p values for comparison. The total annular zone was divided into four quadrantal zones and six annular zones (bandwidth = 0.73 mm). No significant difference in the microvascular density within each annular zone and all quadrantal zones of the superficial and deep layers was found in myopia patients between pre-surgery and post-surgery (Figure 4).

Myopia is one of the most prevalent eye disorders, and the epidemic of high myopia, in particular, is a serious hazard to public health, such as financial, psychological, quality of life, and direct and indirect risks of blindness. ICL implantation is one of the methods to treat myopia. According to our data, ICL implantation is a safe and effective treatment for both moderate and high myopia. No eye loses two or more lines of vision after ICL implantation. All eyes were within ±1.0 D of the attempted correction and both refractive status and IOP remained stable for 3 months after surgery. Its performance in safety, effectiveness, stability, and predictability is even better than the results of Sanders et al. (2004) due to the advancement of surgical techniques and the update of ICL.

Retinopathy is the most common complication of high myopia, which is a slowly progressive and sight-threatening condition. Several studies have investigated the retinal microvascular in patients with myopia, revealing the retinal microvascular network alterations in myopic eyes. The structural elongation of the eyeball mechanically stretches the retinal tissue, resulting in the straightening and narrowing of the microvessels and consequently the decrease of the retinal microvascular density and perfusion in myopic eyes (Li et al., 2017; Leng et al., 2018; Li et al., 2018; Milani et al., 2018; Gołębiewska et al., 2019; Guo et al., 2019). Jiang et al. (2021) found that the superficial and deep macular microvascular density in high myopia was significantly higher than that in non-high myopia by using OCTA; Liu M et al. (2021) also reached the same conclusion in a larger sample study and found a negative correlation between microvascular density and axial length.

OCT angiography, as an advanced imaging technique characterized by non-invasiveness, quantification, and reliability, which can detect blood flow signals in the retina, has superior advantages over traditional angiography techniques. OCTA is widely used in the evaluation and diagnosis of eye diseases, such as high myopia retinopathy (Grudzińska and Modrzejewska, 2018), glaucoma optic nerve damage (Rao et al., 2020), retinal vein occlusion (Hirano et al., 2021) and diabetic retinopathy (Sun et al., 2021). Using OCTA, images from different layers of the retina can be projected clearly due to its high resolution. In the present study, by using OCT angiography, superficial and deep retinal capillary density were measured in moderate and high myopia patients who underwent ICL implantation between pre-surgery and post-surgery. The OCTA provided the macular perfusion of a 6 mm × 6 mm area, we calculated the microvascular density in each region through the box-counting method after correcting for magnification. Our data showed that ICL implantation surgery would not leave adverse effects on the retinal capillary network.

Moreover, clinical evidence suggests that eye surgery would cause the alteration of retinal microcirculation (Alnawaiseh et al., 2018; Kim et al., 2018; Liu J et al., 2021). Pilotto et al. (2019) found that the perfusion of the retinal microvascular plexus in the deeper layers of the macula increased after uncomplicated cataract surgery, which may be related to the early postoperative local inflammatory response. Analogously, Chen et al. (2017) used a retinal oximeter to detect retinal oxygen desaturation due to retina oxygen deficiency after ICL implantation. ICL implantation surgery as a safe and effective refractive surgery plays an important role in correcting moderate and high myopia. However, due to the unusual anatomy and physiology of the retina in high myopia eyes, it deserves our attention for any microcirculation abnormality inherent to ICL implantation surgery. Using OCTA, ophthalmologists can easily assess patients’ retinal microvascular health and disease, which might be beneficial for pre-operative evaluation of ICL implantation surgery and the detection of postoperative complications.

There were a few limitations to this study. Since the levels of microvascular density in the retinal capillary plexuses after ICL surgery detected by OCTA were stable in this study, the sample size could not be calculated. Although we have included as many participants as possible in this study, the number of patients was relatively small and the follow-up period was only 3 months. In bigger populations and during longer follow-up periods, retinal microvascular change may be seen. Besides, because most of the patients who underwent ICL implantation were young people, this study did not include children and the elderly, whose preoperative retinal microcirculation is slightly different (Leng et al., 2018; Golebiewska et al., 2019), and might respond differently to ICL implantation surgery. Moreover, the OCTA scan area used in this study is 6 mm × 6 mm around the macula. Although it has a wider scan range, it has not achieved the best presentation on retinal microvasculature.

In conclusion, this study demonstrates that ICL implantation is an effective treatment for both moderate and high myopia in young patients, with excellent safety, predictability, and stability. Simultaneously, using OCTA, this research provides evidence that ICL implantation has no adverse effects on retinal microvascular. Further larger sample sizes and longer-term studies are warranted to confirm the conclusions presented herein.