Study design and patients
This was a retrospective study of patients who underwent EVO-ICL surgery at Wuhan Bright Eye Hospital between October and December 2019. This study was approved by the Ethics Committee of this Hospital. The written informed consent was obtained from all patients.
The inclusion criteria were: 1) age: 21–45 years; 2) anterior chamber depth (ACD) > 2.8 mm; 3) corneal endothelial cell density (ECD) > 2000/mm²; and 4) completed EVO-ICL surgery and follow-up in this hospital. The exclusion criteria were: 1) other eye diseases such as cataracts and glaucoma that caused visual loss; 2) systemic diseases such as diabetes, autoimmune diseases, or collagen diseases that could affect postoperative healing; or 3) being unable to measure vaulting due to unclear intraoperative OCT images.
Preoperative Measurement
The preoperative diopter, corrected visual acuity (CVA), white-to-white distance (WTW), IOP, ACD, anterior chamber volume (ACV), crystalline lens rise (CLR), axial length, and ECD were recorded. During surgery, the RESCAN 700 system (Carl Zeiss GmbH, Oberkochen, Germany) was used to measure EVO-ICL vaulting. Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) were checked using an international standard visual acuity chart (converted into logMAR visual acuity).
Subjective and objective refractions were performed using a CV-5000 comprehensive refractometer (Topcon Corporation, Tokyo, Japan). The anterior ocular segment was determined using an SL-115 Classic slit lamp microscope (Carl Zeiss GmbH, Oberkochen, Germany). A Pentacam HR three-dimensional panoramic analyzer for the anterior segment (Oculus, Wetzlar, Germany) was used to check corneal morphology, ACV, CLR, and WTW. A CT-800 non-contact tonometer (Topcon Corporation, Tokyo, Japan) was used to measure IOP. An IOL Master 700 biometer (Carl Zeiss GmbH, Oberkochen, Germany) was used to measure ACD and axial length. An SP-3000P corneal endothelial cell counter (Topcon Corporation, Tokyo, Japan) was used to measure corneal ECD. Fundoscopy was performed using a V90C non-contact slit lamp pre-set lens (Halma plc, Amersham, UK). Intraoperative vaulting was observed by using a RESCAN700 microscope (Carl Zeiss GmbH, Oberkochen, Germany). SD-OCT was used for scan imaging, and the ImageJ software was used to measure the ICL vault value. A CIRRUS HD-OCT (Carl Zeiss GmbH, Oberkochen, Germany) was used to measure the distance between the posterior surface of the EVO-ICL and the anterior lens capsule, namely the vault value. All measurements were performed by an ophthalmologist with 9 years of professional experience.
EVO-ICL Surgery
All procedures were performed by the same ophthalmologist with 4 years of professional experience. The size of the EVO-ICL was determined based on WTW, ACD, ACV, and CLR. The online system provided by the manufacturer was used to calculate the EVO-ICL diopter (STAAR Surgical Co., Monrovia, CA, USA). At 3 days before surgery, levofloxacin eye drops (Santen Pharmaceutical Co., Ltd., Osaka, Japan) were continuously administrated at 4 times/day. At 30 min before surgery, compound tropicamide eye drops (Santen Pharmaceutical Co., Ltd., Osaka, Japan) were used for mydriasis. Oxybuprocaine hydrochloride eye drops (Santen Pharmaceutical Co., Ltd., Osaka, Japan) were used to perform surface anesthesia. The axis of corneal astigmatism was marked under the slit lamp before surgery. Conventional disinfection and draping were conducted. The conjunctival sac was washed. The main incision was made at the steepest meridian of the cornea. A syringe was used to inject the EVO-ICL into the anterior chamber. An appropriate amount of 15 mg/ml medical sodium hyaluronate gel (Hangzhou Singclean Medical Products Co., Ltd., Hangzhou, China) was injected above the EVO-ICL to maintain the ACD. The four angles of the EVO-ICL were adjusted to the ciliary sulcus behind the iris with the adjustment hook, and the EVO-ICL was adjusted to the marked area and the residual viscoelastic in the anterior chamber. An Icare rebound tonometer (Icare Finland Oy, Vantaa, Finland) was used to measure the IOP, which was controlled at 15–18 mmHg by replenishing and releasing aqueous humor. A RESCAN 700 microscope (Carl Zeiss AG, Oberkochen, Germany) was used to perform the SD-OCT scan imaging. The five-line scanning mode was used, with a scanning depth of 2.0 mm and a scanning length of 2.0 mm. The distance between the posterior surface of EVO-ICL and anterior lens capsule was observed, and the snapshot mode was used to save the screenshot after clearing. After the end of the surgery, tobramycin dexamethasone eye drops (Alcon-Couvreur SA, Puurs, Belgium) were used.
Intraoperative Measurement Of Vaulting
A RESCAN 700 (Carl Zeiss AG, Oberkochen, Germany) was used for intraoperative imaging, and SD-OCT was used for scanning imaging. For intraoperative SD-OCT image export, the ImageJ software (version 1.48) was used for processing, and the scanning depth was adjusted to 2.0 mm. The distance between the posterior surface of EVO-ICL and anterior lens capsule was measured. All measurements were conducted three times, and the average values were recorded, namely the intraoperative vaulting values.
Follow-up
All patients were followed routinely at 1 month after surgery. The distance between the posterior surface of the EVO-ICL and anterior lens capsule (namely, the vaulting value) was measured using a CIRRUS HD-OCT (Carl Zeiss AG, Oberkochen, Germany). Under the same indoor light, all measurements were performed by the same ophthalmologist three times, and the average values were recorded. For the vault at 1 month after surgery, 250–750 µm was defined as normal vaulting, < 250 µm as low vaulting, and > 750 µm as high vaulting [27, 28]. At the same time, visual acuity, IOP, and diopter were measured.
Statistical analysis
SPSS 22.0 (IBM Corp., Armonk, NY, USA) was used for data processing and statistical analyses. Normally distributed continuous data (according to the Kolmogorov-Smirnov test) were presented as means ± standard deviations and analyzed using Student’s t-test. Non-normally distributed data were presented as medians (ranges) and analyzed using the Mann-Whitney U-test. Categorical data were presented as frequencies (percentage) and analyzed using the chi-square test or Fisher’s exact test. For the multivariable analysis, high vaulting at 1 month after surgery was used as the dependent variable, and the factors with between-group differences (P < 0.05) in the univariable analyses (enter method) were used as the independent variables. Binary logistic regression analysis was performed. Linear correlation analysis was performed regarding the intraoperative and postoperative vaulting. Two-sided (except for the chi-square test) P-values < 0.05 were considered statistically significant.