Implantation of the posterior chamber phakic Visian Implantable Collamer Lens (ICL) (STAAR Surgical AG, Nidau, Switzerland) has been proved to be an effective and predictable method of correcting high myopia.1–3 Numerous studies have proved its safety, and the incidence of moderate and severe complications is low.4–8 However, complications (eg, postoperative intraocular pressure [IOP] increase, endothelial cell loss, and inflammation) have been reported and may cause long-term safety concerns.2,9
Since the emergence of ophthalmic viscosurgical device (OVD) in the 1980s, endothelial cell protection and anterior chamber stabilization have been its main roles during ophthalmic surgeries.10 As in other anterior segment operations, OVD has been used in ICL implantation surgery since the first case in 1993.11 However, the use of OVD could bring its own complications. OVD removal can last up to several minutes and sometimes can be difficult to clear, especially behind the ICL in the posterior chamber. Retained OVD can obstruct the trabecular meshwork and lead to postoperative IOP spikes in the early period after surgery.12 The dramatically increased IOP could further cause endothelial cell damage.13 Moreover, too much OVD in the anterior chamber would prolong the process of ICL unfolding, sometimes even causing ICL inversion.14 Thus, to avoid such complications, OVD is used less often by experienced surgeons during ICL implantation.
The minimum OVD technique has been widely adopted by experienced surgeons in recent years. The ICL is inserted into the anterior chamber without any OVD and only a minimal amount of OVD is injected to adjust the ICL into the posterior chamber. This approach could minimize the OVD retained in the posterior chamber and simplify the OVD removal. This study evaluated the safety of the minimum OVD technique compared with the standard procedure, especially the effects on IOP and endothelial cell loss.
Patients and Methods
This was a retrospective cohort study conducted at the Department of Ophthalmology, Peking Union Medical College Hospital. The study was approved by the Ethics Committee of Peking Union Medical College Hospital. The tenets of the Declaration of Helsinki were followed throughout the study and written informed consents were obtained from all patients.
Patients who received ICL implantation with the minimum OVD technique from January to May 2018 were consecutively enrolled in the minimum OVD group. Patients who received ICL implantation with the standard technique from January to May 2016 were assigned to the standard OVD group. All patients were followed up for at least 12 months. Exclusion criteria were inadequate follow-up time (less than 12 months), missing tests during the follow-up, and previous ophthalmic disease.
Before surgery, a comprehensive ophthalmic examination was performed, including manifest refraction, cycloplegic refraction, corrected distance visual acuity (CDVA), IOP (Topcon CT-80A Computerized Tonometer; Topcon Tokyo, Japan), slit-lamp biomicroscopy, corneal topography (Tomey TMS-4; Tomey Nagoya, Japan), aqueous depth (AQD), white-to-white (WTW) distance, central corneal endothelial cell density (ECD) count, and dilated fundus examination.
The AQD was measured with anterior segment optical coherence tomography (AS-OCT) (Visante AS-OCT 1000; Carl Zeiss Meditec, Dublin, CA) as previously described.15,16 In brief, the enhanced anterior segment single mode (scan length, 16 mm; 256 A-scans) was applied to capture images at the nasal and temporal angle quadrants (3- and 9-o'clock meridians). The highest quality image showing a vertical line orthogonal to the anterior corneal curvature was selected for analysis. Preoperative AQD was measured from the corneal endothelium to the anterior surface of the crystalline lens. WTW distance was obtained manually using a caliper under the slit lamp from the outer margin of the transition zone between the cornea and sclera to the opposite side of it. ECD count was measured using the specular microscope (SP-3000P; Topcon). The measurement was taken automatically over an area of 0.25 × 0.5 mm2 covering the central region of the corneal apex.
The ICL with a central hole (EVO Visian ICL; STAAR Surgical AG) was chosen for all patients. Lens size was calculated through the same protocol based on WTW distance and AQD, according to the manufacturer's suggestion. The ICL power calculation was performed by the manufacturer using a modified vertex formula. Emmetropia was selected as the target refraction for all eyes.
All surgeries were performed by one experienced surgeon (YLuo). In the minimum OVD group, no OVD was injected into the anterior chamber before the insertion of the ICL. After a 3-mm, two-step clear corneal incision was made, the ICL was immediately inserted using an injector cartridge (STAAR Surgical AG) without any OVD. Figure A (available in the online version of this article) shows the wound configuration of the main corneal incision site at postoperative day 1. Instead of OVD, a few drops of balanced salt solution were added to the injector cartridge to keep the ICL hydrated. After the ICL was inserted, a minimal amount of OVD (Amvisc; Bausch & Lomb, Shandong, China) was injected in front of the ICL to adjust it into the posterior chamber. Then OVD was washed out of the anterior chamber using a balanced salt solution with a manual irrigation and aspiration system. In the standard OVD group, all procedures were done as previously described.8,9,17 In brief, a regular amount of OVD (Amvisc) was placed in the anterior chamber before the insertion of the ICL. Then the ICL was placed into the posterior chamber and the OVD was washed out with the same maneuver mentioned above. The same cohesive OVD (Amvisc) was used in both groups throughout the study, which contained 17 mg/mL of pure sodium hyaluronate with a molecular weight of 1 to 2.9 million Daltons and a viscosity at 25°C of 40,500 ± 6,000 mPa.s (at 1.0 s−1). The amount of OVD used in the minimum OVD group was approximately one-third of the standard OVD group.
Anterior segment optical coherence tomographic image of the corneal incision site on postoperative day 1. A two-step wound configuration (white arrow) was observed.
Postoperative Data Collection
Postoperatively, a combination of antibiotic (levofloxacin; Santen, Osaka, Japan) and corticosteroid drops (loteprednol etabonate; Bausch & Lomb, Rochester, NY) were administered topically six times daily for 3 days, after which the doses were gradually tapered and discontinued within 10 days. Data for uncorrected distance visual acuity (UDVA), CDVA, lens vault, and AQD were collected at 1 week and 1, 3, 6, and 12 months postoperatively. IOP was monitored 1, 2, and 3 hours, 1 day, 1 week, and 1 and 3 months postoperatively. If the postoperative IOP exceeded 35 mm Hg, paracentesis would be done through the existing side port to evacuate aqueous humor or diluted OVD remnants and recorded in the medical documents. ECD was measured at 1, 3, 6, and 12 months postoperatively. Postoperative AQD was measured from the corneal endothelium to the anterior surface of the implanted ICL. Lens vault was measured by the AS-OCT with the same procedure as mentioned above and defined as the distance from the posterior surface of the ICL to the anterior crystalline lens pole.
SPSS software (version 22.0; SPSS, Inc., Chicago, IL) was applied for the statistical analysis. The Kolmogorov–Smirnov test was used to confirm data normality. The data were given as mean ± standard deviation. The paired t test was used to evaluate the differences between preoperative and postoperative measurements within the group. Student's t tests was applied to evaluate the differences of measurements between groups. The chi-square or Fisher's exact test was used for the analysis of categorical data. A P value of less than .05 was considered statistically significant.
A total of 147 eyes of 74 patients were collected in the minimum OVD group and 154 eyes of 77 patients in the standard OVD group. Table 1 summarizes the preoperative patient characteristics of the two groups. No significant differences were found between the two groups in baseline parameters.
Safety and Effectiveness
All surgeries were uneventful, and no intraoperative complications were observed. No postoperative adverse events were recorded in either group, except for the expected changes in IOP and ECD. No cataract formation was observed in either group during the 12-month follow-up. No significant difference was found in visual outcomes between the two groups at all follow-up time points (data not completely shown). Figure 1 shows the visual outcomes of the two groups at 12 months after surgery as an example.
Visual outcomes of the minimum ophthalmic viscosurgical device (OVD) group and standard OVD group at 12 months after surgery. UDVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity. D = diopters
Lens Vault and AQD
Although lens vault gradually decreased with time, the difference was insignificant between groups at each postoperative follow-up time point (Table 2). The postoperative AQD, measured from the corneal endothelium to the anterior surface of the implanted ICL, decreased significantly at 1 week after surgery compared with the preoperative data in both groups (P < .001) and remained stable afterward. No significant differences in AQD were found between the two groups at all time points (Table 2).
Postoperative LV and AQD at Different Time Points
The postoperative IOP was more stable in the minimum OVD group compared with the standard OVD group (Figure 2). The minimum OVD group had significantly lower IOP than the standard OVD group at 2 hours (17.04 ± 4.21 vs 19.40 ± 6.78 mm Hg, P < .001) and 3 hours (15.12 ± 3.38 vs 17.15 ± 5.09 mm Hg, P < .001) postoperatively. In the minimum OVD group, the IOP was significantly higher than the baseline at 1 hour (17.85 ± 5.72 vs 15.95 ± 3.29 mm Hg, P < .001) and 2 hours (17.04 ± 4.21 vs 15.95 ± 3.29 mm Hg, P = .002) postoperatively, and the IOP peak appeared at 1 hour postoperatively. In the standard OVD group, the IOP peak appeared at 2 hours postoperatively and the IOP was significantly higher than the baseline at 1 hour (16.54 ± 5.26 vs 15.43 ± 2.70 mm Hg, P = .032), 2 hours (19.40 ± 6.28 vs 15.43 ± 2.70 mm Hg, P < .001), and 3 hours (17.15 ± 5.10 vs 15.43 ± 2.70 mm Hg, P = .001) postoperatively. The IOP gradually decreased to the preoperative level and no differences were found between the two groups after 24 hours. The occurrence rate of paracentesis was significantly less in the minimum OVD group compared with the standard OVD group (0.68% [1 of 147] vs 3.2% [5 of 154], P < .001).
Mean intraocular pressure (IOP) of the minimum ophthalmic viscosurgical device (OVD) group and standard OVD group at each follow-up time point. *P < .001, two-tailed t test. The error bar indicates the standard deviation.
The ECD gradually decreased with time in both groups after surgery, but there was no significant difference between groups at each follow-up time point (Figure 3). In the minimum OVD group, the ECD reduced 1.7% from 2,824 ± 247 cells/mm2 preoperatively to 2,775 ± 248 cells/mm2 at 12 months postoperatively (P = .092). In the standard OVD group, the ECD reduced 1.6% from 2,742 ± 258 cells/mm2 preoperatively to 2,697 ± 263 cells/mm2 at 12 months postoperatively (P = .136). There was no difference in the change of ECD at 12 months between the two groups (minimum OVD group: −42 ± 144 cells/mm2; standard OVD group: −36 ± 126 cells/mm2; P = .701).
Mean endothelial cell density (ECD) of the minimum ophthalmic viscosurgical device (OVD) group and standard OVD group at 1, 3, 6, and 12 months postoperatively. No significant differences were found between the two groups at each follow-up time point. The error bar indicates the standard deviation.
Many efforts have been made to improve the safety of the ICL for correcting high myopia. The minimum OVD technique is adopted in practice to simplify the surgical procedure and minimize OVD-related complications. To our best knowledge, no studies have evaluated the safety of this technique yet. Our study revealed that the minimum OVD technique could reduce the IOP fluctuations immediately after surgery and would not cause any extra damage to the endothelial cells compared with the standard technique.
OVDs are widely used in ophthalmic surgeries. A major concern of OVD is that it could cause mechanical obstruction of the trabecular meshwork if it is not cleared thoroughly, which could further induce an increase in IOP after surgery.18,19 Elevated IOP may be associated with pain, corneal epithelial edema, and optic disc damage. OVD retention may cause elevated IOP higher than 30 mm Hg in 23% of cases with high viscosity OVD.20 Svedbergh13 found IOP peaks up to 35 mm Hg can cause corneal endothelial cell damage and loss in the vervet monkey. Acute IOP elevation to 30 mm Hg and above could trigger immediate impairment of fine visual discrimination within the central visual field in non-human primates.21 Given that most of the ICL patients are highly myopic, they are associated with a greater risk of glaucomatous optic neuropathy and more vulnerable to IOP fluctuations.22,23 This could be a problem because most of the ICL patients have surgery in the outpatient clinic and are discharged shortly after surgery. Hence, a thorough removal of OVD may be vital to prevent dangerous IOP spikes and the consequent side effects. With the standard procedure, OVD might be trapped behind the ICL, making it difficult to remove, whereas the minimum OVD technique avoids such a problem. Our data revealed minimizing the amount of OVD could induce earlier and lower IOP peaks after ICL implantation surgery. To avoid possible endothelial damage, paracentesis was done for cases with IOP higher than 35 mm Hg in our study and the minimum OVD technique also significantly reduced the chances of paracentesis. The IOP of both groups returned to baseline after 24 hours, which means the IOP spike was transient and might be overlooked sometimes.
Any procedure involving the anterior segment would provoke endothelial cell loss and ECD is one of the main parameters used to evaluate the safety of the ICL.9 Endothelial cell loss due to aging is estimated to be 0.5% per year, and younger patients have a faster annual rate of endothelial cell loss.24,25 ECD loss after ICL implantation is highest during the first year, varying between less than 0.3% and 6.8%.2,8,26,27 The difference in the ECD loss from different study groups may be due to the surgical technique, the ICL model, the measurement device, and the age of the patients. The rate of corneal endothelial cell loss usually slows down after 12 months postoperatively.17,27 Our study revealed minimum OVD would not cause any extra damage to the endothelial cells and the percentage of ECD loss at 12 months postoperatively is within the safety range. In the area of other anterior segment surgeries, Schargus et al.28 compared femtosecond laser–assisted cataract surgery with and without OVD and also found no significant difference in endothelial cell loss 6 months postoperatively. However, all of these operations were done by senior and experienced surgeons, and the minimum or no OVD approach raised a much higher requirement for the surgeon's experience and technique.
The EVO ICL with a central hole adopted in our study allows a more natural flow of the aqueous humor, which reduces the chances of cataract formation and eliminates the need for peripheral iridotomies.29,30 The OVD left behind the ICL might block the central hole and induce acute pupillary block after surgery, and this possibility is technically eliminated with the minimum OVD approach. No anterior subcapsular cataract or acute pupillary block was observed during the 12-month follow up. Our study also found a gradual decrease of the lens vault with time, which was in accordance with previous studies.3,8 The significant decrease of AQD after surgery was due to different measurement starting points and was consistent with previous findings.2 The stable postoperative visual acuity of both groups in 12 months also proves it is a safe and predictable procedure.
The study also has several limitations. First, the sodium hyaluronate used in our study is a high viscosity cohesive OVD, which tends to induce relatively higher postoperative IOP spikes.19,31 For the safety of lower viscosity dispersive OVDs, more studies might be needed to confirm the results. Second, our conclusion is based on the fact that surgeons are well trained and have stable performance. The technique may not be applicable for beginners. Studies with a longer follow-up time may be needed to observe the complications in the long term.
The minimum OVD technique could allow surgeons to perform ICL implantation without additional risk to the corneal endothelial cells. It could achieve comparable visual and structural outcomes to the standard procedure, while reducing the IOP fluctuations after surgery.
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|Characteristic||Minimum OVD Group (n = 147)||Standard OVD Group (n = 154)||Pb|
|Age (years)||27.02 ± 6.06||28.21 ± 5.64||.304|
|Sex (male / female)||32 / 115||38 / 116||.551|
|Cycloplegic SE (D)||−9.37 ± 3.61||−10.29 ± 3.06||.913|
|Cycloplegic cylinder (D)||−1.18 ± 1.00||−1.31 ± 1.08||.243|
|Flat K (D)||43.06 ± 1.43||43.30 ± 1.51||.339|
|Steep K (D)||44.38 ± 1.69||44.62 ± 1.55||.355|
|CDVA (logMAR)||0.08 ± 0.12||0.06 ± 0.11||.339|
|WTW distance (mm)||11.73 ± 0.42||11.84 ± 0.40||.319|
|AQD (mm)||3.20 ± 0.33||3.19 ± 0.22||.568|
|AL (mm)||26.96 ± 2.25||27.20 ± 1.35||.226|
|CCT (µm)||526.01 ± 40.40||507.62 ± 86.40||.857|
|IOP (mm Hg)||15.95 ± 3.29||15.43 ± 2.70||.146|
|ECD (cells/mm2)||2824 ± 247||2742 ± 258||.755|
|ICL size (mm)||12.63 ± 2.12||12.76 ± 0.33||.379|
|ICL power (D)||−10.72 ± 3.43||−11.18 ± 3.08||.768|
Postoperative LV and AQD at Different Time Pointsa
|Characteristic||Minimum OVD Group (n = 147)||Standard OVD Group (n = 154)||Pb|
| 1 week||0.62 ± 0.17||0.60 ± 0.19||.184|
| 1 month||0.60 ± 0.17||0.59 ± 0.19||.156|
| 3 months||0.59 ± 0.19||0.58 ± 0.14||.190|
| 6 months||0.59 ± 0.17||0.56 ± 0.20||.236|
| 12 months||0.54 ± 0.13||0.52 ± 0.17||.220|
| 1 week||2.30 ± 0.24||2.38 ± 0.24||.934|
| 1 month||2.33 ± 0.25||2.37 ± 0.26||.716|
| 3 months||2.33 ± 0.21||2.37 ± 0.26||.369|
| 6 months||2.32 ± 0.28||2.37 ± 0.25||.344|
| 12 months||2.40 ± 0.19||2.40 ± 0.23||.240|