Analysis of the Correlations between Changes in Posterior Segment and Anterior Chamber Segment after Implantable Collamer Lens Implantation in Highly Myopic Patients

doi:10.21203/rs.3.rs-5286545/v1

Purpose

To investigate the effects of implantable collamer lens (ICL) implantation on the posterior segment of the eye and its correlation with the structural changes of the anterior chamber angle in patients with high myopia.

Methods

Patients with high myopia undergoing ICL surgery from September 2022 to June 2023 were selected as the surgical group, while those with high myopia not undergoing surgery during the same period served as the non-surgery group. The patients in the surgical group underwent assessments for uncorrected distance visual acuity (UDVA), intraocular pressure (IOP), refraction, anterior segment optical coherence tomography (AS-OCT), optical coherence tomography (OCT), and optical coherence tomography angiography (OCTA) preoperatively, and on 1 day, 1 week, 1month, and 3 months postoperatively. In contrast, the patients in the non-surgery group were evaluated at the baseline and three months later.

Results

Conclusion

Anterior chamber depth narrowed after ICL implantation, which remained stable at 3 months postoperatively. The superficial vessel density fluctuated postoperatively, returning to preoperative levels by 3 months. The deep vessel density (DVD) also fluctuated, with the nasal quadrant around the fovea showing an increase in DVD at 3 months postoperatively compared to preoperatively, while DVD in other areas returned to preoperative levels by 3 months. The fluctuations in vascular density postoperatively correlated with changes in the anterior chamber angle structure. ICL implantation demonstrates good safety and efficacy for patients with high myopia.

ICL Implantation

Anterior Chamber Angle Structure

Retinal Vascular Density

High myopia, a category of refractive error with myopia greater than 600 diopters, accompanied by axial elongation and degenerative changes in the retinal and choroidal layers of the eye¹. Implantable collamer lens (ICL) implantation is currently a widely adopted effective method for the correction of high myopia. Its efficacy and stability have been extensively validated through numerous studies^2–4. Patients can gain improved and stable visual quality, with a smaller increase in total higher-order aberrations⁵, and show greater long-term stability in refractive outcomes postoperatively⁶.

The ICL is fixed within the iridociliary sulcus, and its implantation can affect the anterior chamber structure. Previous reports have documented adverse complications such as glaucoma, shallow anterior chamber, corneal endothelial damage, and complicated cataract following ICL implantation³. Numerous studies indicate that after ICL implantation, there are significant reductions in the anterior chamber angle, volume, and depth^7–10.

Current studies have reached inconsistent conclusions regarding the effects of ICL implantation on fundus blood flow, choroid, and optic nerve fiber layer. Xu et al.¹¹ found that ICL implantation in highly myopic eyes increased retinal thickness in all paracentral recess regions and decreased RNFL thickness in the temporal optic disc, FAZ region, and blood density in certain retinal layers. But Pachon et al.¹² found no significant change in mean RNFL thickness. Zhu et al.¹³ observed increased retinal thickness, CT, and plexiform layer thickness in 73 eyes, with no significant change in retinal capillary density. All of the above studies have addressed the early changes in retinal function after ICL to some extent, but the parameters studied differed, some conclusions were divergent, and the reasons for the changes in some parameters were analyzed differently.

Therefore, in this study, we measured the anterior chamber angle and posterior segment structure using OCT and OCTA, respectively, to observe the changes in the anterior chamber angle and posterior segment structure after ICL implantation in highly myopic eyes, to investigate the effects of ICL implantation on the fundus SVD, DVD, and FAZ area, and to clarify whether the changes in the posterior segment structure are related to the changes in the structure of the anterior chamber after the operation, so that the effects of ICL implantation on the safety of the fundus in patients with high myopia can be better evaluated in clinical treatments.

Study Designs and Patients

This study was a prospective study. Patients who underwent ICL surgery from September 2022 to June 2023 and non-surgical patients during the same period were included and enrolled into surgical group and non-surgery group. The study was approved by the Ethics Committee and followed the principles of the Declaration of Helsinki throughout (Implementation of Research Ethics Approval No. GZAIER2023IRB25; China Clinical Trial Record No. MR-44-24-009241). All subjects read and signed the informed consent form before participating in this study.

Inclusion Criteria for Surgery Group

(1) The patients themselves have the desire to improve their refractive status by ICL surgery; (2) Myopic patients with refractive error not less than -6.00 D, or eye axis ≥26 mm; relatively stable (refractive error change ≤0.50 D per year for 2 consecutive years); (3) Central anterior chamber depth ≥2.8 mm; (4) Corneal endothelial cell density ≥2,000 cells/mm²; (5) No progressive clouding of the lens; (6) No uncontrolled glaucoma; (7) No cone cornea, severe dry eye, active ocular lesions or infections; (8) No history of diabetes, hypertension, autoimmune disease, hematologic disease, systemic connective tissue disease or other systemic diseases, and no history of taking related medications; (9) Normal fundus retina or retinal tear who has undergone retinal laser photocoagulation; (10) No history of eye surgery or trauma; (11) Age above 21 years old; (12) The patient is willing to cooperate with the follow-up observation.

Inclusion Criteria for Non-surgery group

Patients who meet the above items (2) to (12) but have no intention to undergo ICL/TICL surgery within six months for the time being.

Exclusion criteria

(1) Patients who are mentally or psychologically abnormal, unable to understand the risks of surgery or have unrealistic expectations; (2) Those who are unable to complete follow-up visits; (3) During pregnancy or breastfeeding.

Preoperative and postoperative examinations

Routine Examination

All patients in the surgical group underwent routine preoperative examinations, including uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), computerized refraction, cycloplegic refraction, non-contact intraocular pressure (IOP), slit-lamp examination, corneal topography, corneal biomechanics, axial length (AL), central corneal thickness (CCT), ultrasonic biologic microscopy (UBM), corneal endothelial cells, and scanning laser ophthalmoscopy (SLO).The non-surgery group did not undergo UBM examination, with all other routine examinations being the same as the surgical group.

AS-OCT, OCT and OCTA Examination

All patients underwent AS-OCT examination, which was done by the same skilled technician who had received standard training and passed the examination skills test for the relevant instrument. Anterior chamber angle structural parameters such as AOD, ARA, TIA, and TISA measured at 250, 500, and 750 μm were recorded. (Figure 1)

All patients underwent OCT and OCTA examinations, which were performed by the same skilled technician who had received standardized training and passed the relevant instrumental examination skills test. Angio Retina (3×3mm), HD Angio retina (6×6mm), Grid, ONH and Angio Disc modes were selected for scanning respectively. Images with an imaging quality score >6 or clear as a slice were selected for inclusion in the analysis. foveal avascular zone (FAZ) area, choroidal thickness (CT), SVD, DVD, retinal nerve fiber layer (RNFL) thickness and disc retinal perfusion capillary vessel density (DRVD) were recorded (Figure 2).

CT measurements were taken from the outer edge of the RPE layer to the inner edge of the choroidal layer, averaging horizontal and vertical orientations at the macular central sulcus nadir, as shown in Figure 3a. FAZ area was measured in Angio Retina (3 × 3 mm) mode, spanning from 10 μm below the inner border membrane to 10 μm above the outer plexiform layer, as shown in Figure 3b. DRVD measurements were based on the percentage of the area occupied by the vascular system of the RPC plate, from the inner border membrane to the nerve fiber layer, as detected in HD Angio Disc mode, as shown in Figure 3c.

The RNFL thickness was obtained based on ONH scanning measurements within a 3.4mm diameter circle centered on the optic disk, as shown in Figure 4.

Surgical procedure and postoperative medication

All surgeries were performed by the same experienced surgeon (Z.W). Patients in the surgical group used 0.5% levofloxacin eye drops (Santen, Japan) four times daily for three days prior to surgery. Preoperative preparations included full pupil dilation and topical anesthesia with oxybuprocaine eye drops (Santen, Japan). During surgery, a 2.8mm temporal corneal incision was made, and the ICL lens was implanted after viscoelastic injection. The lens haptics were positioned in the ciliary sulcus, and viscoelastic was aspirated. The procedure concluded without complications, and Tobramycin-Dexamethasone Eye Ointment (Santen, Japan) was applied, followed by gauze dressing. Postoperatively, patients used 0.5% levofloxacin and tobramycin-dexamethasone eye drops for one week, and 0.1% sodium hyaluronate eye drops (Ursapharm, Germany) for four weeks, all administered four times daily.

Statistical Analysis

Statistical analysis was conducted using SPSS 26.0 software (SPSS Inc., Chicago, Illinois, USA). All measurement data underwent normality testing with the Kolmogorov-Smirnov test, and were expressed as mean ± standard deviation (mean ± SD). Based on the normality test results, comparisons of differences between preoperative and various postoperative follow-up time points were performed using the paired samples t-test or Wilcoxon rank sum test; inter-group comparisons between the surgical group and the non-surgery group were analyzed using the independent samples t-test or Mann Whitney U test; univariate continuous changes were assessed using repeated measures analysis of variance (Re-ANOVA) or Friedman's test. A statistical difference exists when P<0.05. Spearman correlation analysis was employed to examine the correlation between variables.

Baseline characteristics

In the surgical group, 99 eyes met the inclusion criteria, with 36 eyes completing the 3-month follow-up. In the non-surgical group, 39 eyes met the criteria, with 23 completing the follow-up. Baseline characteristics are detailed in Tables 1-4. The control group had lower UDVA than the surgical group, with no significant differences in age, AL, refractive error, CCT, and IOP. The control group also showed slightly higher nasal and temporal ARA250, temporal ARA750, and temporal TISA250, but these differences were not statistically significant. The surgical group had lower SVD, higher nasal RNFL thickness, and lower temporal RNFL thickness, with no significant differences in DVD, subfoveal CT, and superior/inferior RNFL thickness between the groups.

Table 1 Baseline characteristics in two groups

	surgical group	non-surgery group
Age (years)	27.86±4.43	27.61±2.17
UDVA (logMAR)	1.23±0.27^*	1.47±0.31^*
Diopter (D)	-8.64±1.71	-8.58±1.38
AL (mm)	26.98±1.19	27.25±0.56
ACD (mm)	3.20±0.25	3.24±0.24
CCT (μm)	533.56±27.36	541.70±29.64
IOP (mmHg)	18.03±1.97	17.35±2.29