Implantable contact lens (ICL) is a refractive lens that is placed in the posterior chamber of the eye behind the iris before the lens is fixed in the ciliary sulcus and is designed to arch anteriorly at a certain height to avoid contact with the anterior lens capsule. The predictability, effectiveness, safety, and stability of ICL for myopia correction have been well documented [1-5], along with some reports of short- and long-term potential complications after ICL surgery, such as anterior lens capsule cataract, iris pigment loss, peripheral anterior chamber shallowing, and pupillary block glaucoma. The occurrence of these complications is related to the distance between the ICL and the natural lens. the distance between the posterior surface of the ICL and the anterior lens capsule surface is called the arch height of the lens (vault), and vault is an important indicator used to evaluate the safety of the ICL after implantation. In this study, the arch height was measured 6 months after ICL surgery and correlation analysis was performed to further provide a basis for the safety of ICL.
I. Study subjects and methods
1. Study subjects: 42 cases (77 eyes), 15 men and 27 women, aged 19 to 43 years, including 28 cases under 30 years old, 12 cases between 30 and 40 years old, and 2 cases over 40 years old. The patients had a preoperative spherical lens of -5.0 D to -23.0 DS, with a mean of -12.38 DS. Corneal thickness ranged from 459 to 621µm, with a mean of 523µm. Best corrected visual acuity: 0.2 to 1.2. All patients met the following conditions: corneal transverse diameter ≥10.8 mm, anterior chamber depth ≥2.8 mm, normal intraocular pressure (10 to 21 mmHg ), corneal endothelial cell count >2200 cells/mm2., clear lens, and no active ocular inflammation or other eye diseases.
The ICL is calculated by a special software. The refractive power of the ICL is determined by the optometry, corneal curvature, anterior chamber depth, and corneal thickness. The length of the ICL is determined by the transverse corneal diameter (i.e., the distance from 3:00 to 9:00 white to white, W to W). The height (vault), which is the distance between the central posterior surface of the ICL and the anterior lens capsule surface.
2. Surgical approach: Laser peripheral iridotomy is completed 3 days before surgery. The location of the peripheral iridotomy is two holes in each eye at the 10:30 and 1:30 points of the iris. Before ICL implantation, the pupil was dilated sufficiently, and a 3.2-mm wide temporal clear corneal incision was made under surface anesthesia, and the anterior chamber was injected with viscoelastic, and the ICL was implanted into the posterior chamber using a special pushing device from STAAR. Postoperative drops of tobramycin dexamethasone ophthalmic solution were used to spot the eyes for 1 week.
3. Postoperative follow-up: All patients were examined for refractive error, central anterior chamber depth, and gap between the ICL and the clear lens 6 months after surgery.
4. Examination instruments and methods: Oculus’ Pentacam HR three-dimensional anterior segment analysis diagnostic system was used for the examination of the anterior chamber depth and the gap between the ICL and the clear lens. The white-to-white distance was measured under the microscope with calipers, and the examinations were all performed by the same examiner.
5. Statistical analysis method: All data were analyzed using SPSS13.0 statistical software.
II. Results
1.Patients’ general information
Table 1: General information of patients
Parameters Mean SD [min, max]
Age (y) 28.6 7.9 [18, 49]
Spheroscopy (D) -12.91 4.08 [-5, -23]
Columnar lens (D) -1.12 1.05 [0, -4]
Lens length (mm) 11.88 0.34 [11.5, 12.5]
Lens degree (D) -16.68 3.85 [-7.50, -23.00]
White-to-white distance (mm) 11.59 0.35 [10.80, 12.20]
Anterior chamber depth (cm) 3.19 0.27 [2.80, 3.83]
2, Lens gap and anterior chamber depth at 6 months of surgery
The Petencam 3D anterior segment analysis and diagnostic system is used to analyze and scan the anterior segment by Scheimpflug imaging technology, which can measure the anterior chamber depth (ACD) and the gap between the ICL and the clear lens (vault). The postoperative patient follow-up rate at 6m was 84.6% (77/91), with a mean follow-up time of 9.54±4.12 months. Follow-up observation of vault and ACD was performed by 6m after surgery. The mean anterior chamber depth at 6 months after surgery was (2.87±0.28) mm. vault at 6 months after surgery was on average (452±216.38)µm, with a maximum of 1080µm and a minimum of 130µm.
Table 2: Distance (vault) between ICL and lens (6 months postoperatively)
Vault (µm) Number of eyes Proportion
Under 150 3 3.9%
150 to 300 18 25.4%
300～500 30 42.3%
500～700 20 28.2%
Above 700 6 8.5%
2. The multiple regression analysis of vault is shown in Table 3
Pearson correlation analysis, and vault was correlated with white to white distance (r=0.405, p=0.000), length of ICL (r=0.465, p=0.000), and anterior chamber depth (r=0.390, p=0.000) in that order. Multiple regression equation: vault=0.040×ICL length-0.231×W to W+0.138×ACD-2.113; the relationship between vault and white-to-white and ACD are shown in Figure 1 and Figure 2, respectively. the greater the white-to-white distance, the deeper the anterior chamber, the greater the selected ICL length, and the greater the vault after ICL implantation.
Table 3: Multiple regression analysis of vault
Variables Regression coefficient (B) Standardized B P value
ICL length 0.040 0.698 0.000
W to W -0.231 -0.393 0.011
ACD 0.138 -0.205 0.048
Constant -2.113
Adjusted R2 0.294
III. Discussion
A serious complication after ICL surgery is the development of anterior subcapsular cataract. For the mechanism of postoperative cataract, it is generally believed to be related to the injury during surgery, the contact between ICL and lens, the disruption of atrial circulation in the lens after surgery, and the non-specific inflammation in the eye after surgery [3]. Therefore, the arch height (vault) of the ICL in the eye is a key factor in determining the position of the ICL. vault is too small for the ICL to come into contact with the lens and thus lead to cataract, while vault is too large to cause anterior chamber shallowing, iris pigment loss and thus the possibility of glaucoma and corneal endothelial damage [6]. vault is determined by the natural curvature of the ICL design, the length of the ICL and the length of the ciliary sulcus. With a large white-to-white distance, the gap between the ciliary sulcus and the iris is larger, and the pressure of the iris on the ICL is reduced so that the vault gap is larger [7]. So it is very important to study the factors related to vault for the rational selection of ICL size. For the selection scheme of ICL length we adopt a combination of white-to-white distance and anterior chamber depth: when the ACD is between 2.8 and 3.0 mm, the ICL length takes ≤ white-to-white plus 0.5 mm; when the ACD is between 3.0 and 3.4 mm, the ICL length ≥ white-to-white distance plus 0.5 mm, and when the ACD ≥ 3.4 mm, the ICL length ≥ white-to-white plus 1 mm. in In our study, analysis using multiple stepwise regression revealed that vault was significantly correlated with ICL length, white-to-white distance, and anterior chamber depth; the greater the white-to-white distance, the deeper the anterior chamber, and the longer the selected ICL length, the greater the vault. This result is consistent with our initial selection scheme for the lens, and our results suggest that selecting a longer ICL length for patients with a larger white-to-white distance and a deeper anterior chamber can maintain an appropriate vault.
For the specific measurement of vault, the size of vault has traditionally been roughly estimated by comparing the thickness of vault and cornea by slit lamp, and some scholars recommend that the minimum distance of vault should not be less than 10% of corneal thickness (CCT), with the ideal vault being 30% CCT or more [8]. elies et al [9] graded the size of vault It was graded as 0-4, with grade 0 vault being 0, grade 1 100µm, grades 2 to 3 between 200 and 450µm and no contact with the lens around the central arch of the ICL, and grade 4 above 500µm. However, this grading of vault lacks some rationality, because the corneal thickness is not the same in different individuals, generally ranging from 450µm to 600µm, so the estimated value of vault is not accurate. Objective measurements of vault using UBM and OCT have been reported [10] to provide a more accurate view of vault size and recommend 250-750µm as the ideal vault. Gonvers et al [6] reported that vault〉90µm can prevent the occurrence of post-ICL cataract, while vault〉150µmICL would not come in contact with the lens. In our study, the distance vault between ICL and lens was measured using the Petencam Eye Ganglion Measurement and Analysis System. The mean value of vault was 452µm, which is about 1 CCT, with a minimum of 130µm and a maximum of 1080µm. And the vault was between 300µm and 700& micro;m between 70.5% of patients (see Table 2), no cases of ICL and lens contact and vault too large (1.35 mm) were observed. Also the change in vault was not statistically significant during the one year follow-up observation. Due to the short observation period of our cases, long-term results are needed for the changes in vault with age.
Lackner [11] et al. did a 3-year follow-up observation of ICL patients and found that the occurrence of postoperative lens clouding was related to surgical operation injury and age, and the risk of lens clouding was higher in patients over 50 years of age, while it was not related to the distance vault of ICL from the lens. Also the fourth generation lens produced by STAAR has an improved arch height, it is designed with sufficient arch height within the ICL to avoid contact with the anterior lens capsule, so the incidence of cataract is also significantly lower than before [12]. In all cases in our study, no lens clouding developed during the follow-up observation period. Surgical proficiency and skill are critical to the success of the procedure, which is done without touching the lens as much as possible. Lege et al. reported that in 49 patients with ICL surgery, there was a tendency for the vault to decrease with age after surgery [13], analyzing the reason why the lens increases its thickness with age related to the increase in the central thickness of the lens making the lens more convex forward, which would lead to a decrease in the distance between the ICL and the anterior lens capsule with age. kazutaka [14] et al. also analyzed the vault correlation, and found that vault was correlated with white-to-white distance and age; the greater the white-to-white distance, the greater the vault, and the older the patient, the smaller the vault, and their measurement of vault was performed using slit lamp photography and was under the condition of pupil dilation, and vault would be large after pupil dilation, which is related to the fact that the anterior ICL after pupil dilation Without iris compression, Vanessa [15] and domestic Wang Ningli et al [16] found no statistically significant effect on vault in the medically constricted and regulated condition, while pupil narrowing under natural light exposure made the distance between ICL and lens decrease. In our study, the Petencam preocular segment measurement and analysis system measured vault under natural conditions, which removed the influence of pupillary factors on vault and was closer to the normal state of vault. This is also related to the low age of our patients and the short observation period, as 65% of our patients were under 30 years old and only 3 cases were over 40 years old, so further observation is needed on the effect of age on vault.
In our study, there was no correlation between vault and ICL prescription, although according to STARR data, ICL design increases in height and thickness with increasing refraction, with ICL prescriptions ranging from -3.00-23.00 D refraction and total height ranging from 1.19-2.09 mm, with the difference between minimum and maximum prescription height Only 0.9 mm, this height difference has almost no effect on vault size. Some scholars have pointed out that the measured white-to-white distance does not reflect the true horizontal diameter of the ciliary sulcus [17] and suggested that measuring the sulcus-to-sulcus distance of the ciliary sulcus with ultrasound biology (UBM) is more appropriate for determining vault in ICL; Kim et al [10] used a single-variable stepwise regression method to analyze the significant association between the horizontal diameter of the ciliary sulcus measured by UBM and the white-to-white distance, and Je Hyun also analyzed the correlates of vault and found that vault was correlated with white-to-white distance but not with ciliary sulcus diameter, implying that vault was relatively larger for patients with large white-to-white distance and deeper anterior chamber [18]. This is consistent with our results where vault and white-to-white distance are off because for ICL length selection, the deeper the anterior chamber the greater the ICL length selected for the same white-to-white, such that vault is greater.
In our study, we only observed vault at 6 months after surgery, and long-term follow-up observation should be performed for patients after ICL surgery.
IV. Conclusion
Vault correlates with white-to-white distance and anterior chamber depth, and patients with larger white-to-white and deeper anterior chamber have greater relative choice of ICL length and greater vault obtained.
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