To compare vaulting changes in eyes implanted with V4c and V4 implantable collamer lenses (ICLs) under differing lighting conditions.
Noninterventional, cross-sectional comparative observational case series.
Fifty-six eyes of 38 patients implanted with V4c ICLs, and 54 eyes of 28 patients implanted with V4 ICLs were enrolled and analyzed. Anterior chamber depth, pupil size and postoperative vaulting were evaluated using a Visante optical coherence tomography system under photopic and mesopic conditions 1 month postoperatively. Refractive errors, keratometry values, axial lengths, intraocular pressures, anterior chamber volumes, and central corneal thicknesses were also recorded.
No significant differences were noted in anterior chamber depth between photopic and mesopic conditions in either group. Significant decreases in vaulting and pupil size were detected under photopic conditions in both groups. Moreover, vaulting changes in eyes implanted with V4c ICLs were significantly larger than those in eyes implanted with V4 ICLs.
V4c ICL vaulting decreased more prominently under photopic conditions than did V4 ICL vaulting. Therefore, postoperative vaulting under mesopic and photopic conditions should be considered when interpreting the vaulting of eyes implanted with V4c ICLs.
The Visian implantable collamer lens (ICL) (STAAR Surgical, Monrovia, California, USA) is a posterior-chamber phakic intraocular lens that has been reported to be effective for the correction of moderate to high myopia. Although the implantation of an ICL offers outstanding advantages, postoperative complications associated with high or low vaulting (the distance between the posterior surface of the ICL and the anterior surface of the crystalline lens) have been reported by several investigators.
Excessively high vaulting causes mechanical contact between the ICL and the iris, resulting in inflammation, and it increases in intraocular pressure associated with angle-closure glaucoma and pigment dispersion syndrome. Conversely, the close proximity of the ICL to the crystalline lens may cause mechanical contact or inadequate aqueous circulation, which is also problematic because low vaulting between the ICL and the crystalline lens is responsible for a high incidence of anterior subcapsular cataract formation.
Postoperative measurements of ICL vaulting have been mainly static in nature because vaulting measurements are typically performed in predetermined mesopic conditions. However, vaulting can never be essentially static, based on the fact that vaulting changes continuously with dynamic movement according to lighting conditions or the accommodative status of the eye.
The accommodative reaction or pupil constriction in response to light can affect the amount of ICL vaulting. During accommodation, both the forward movement of the anterior surface of the crystalline lens and the decreases in pupil size were shown, thereby decreasing the amount of vaulting. On the other hand, pupil constriction is induced under photopic conditions merely via the light reflex, which is mediated by retinal photoreceptors and subserved by 4 neurons (the sensory, internuncial, preganglionic motor, and postganglionic neurons), finally causing the ICL to move toward the crystalline lens. Studies evaluating changes in vaulting of the ICL under differing lighting conditions showed a significant decrease in central vaulting under photopic conditions.
Recently, the V4c ICL (CentraFLOW technology, STAAR Surgical) was designed with a 360 μm central hole to allow for the natural flow of aqueous humor without the need for iridotomy. The V4c ICL has shown clinical outcomes comparable to those of the conventional V4 ICL. To date, no study has evaluated postoperative vaulting changes according to differing lighting conditions in eyes implanted with V4c ICLs. Therefore, we investigated vaulting changes in eyes implanted with V4c ICLs under photopic and mesopic conditions and compared V4c ICL and V4 ICL vaulting changes. Furthermore, we evaluated the anterior chamber depths (ACDs) and pupil sizes of eyes implanted with V4c and V4 ICLs under photopic and mesopic conditions.
This retrospective, comparative case series was performed with the approval of the Institutional Review Board of Yonsei University College of Medicine (Seoul, South Korea) and conducted in accordance with the tenets of the Declaration of Helsinki and good clinical practices. All patients provided written informed consent.
This study comprised 110 eyes of 66 patients who underwent V4c or V4 ICL implantation in a standardized fashion by the same surgeon (SYK) at the Eyereum Eye Clinic, Seoul, South Korea, between May 2013 and April 2014. The mean patient age was 26.87 ± 5.52 years (range, 20–45 years); 47 patients were women and 19 were men. All subjects were myopic, with a spherical equivalent of −9.43 ± 2.26 diopters (D) (range,−4.00 to −15.87 D). Of 38 patients, 56 eyes received the V4c ICL model, and of 28 patients, 54 eyes received the V4 ICL model. The mean ICL D value was −18.6 ± 2.3 D (range, −11.5 to −23.0 D) in both groups. A further breakdown according to lens size indicated that 14 eyes (25%) were implanted with a size 12.1 lens, 37 eyes (66%) with a size 12.6 lens, and 5 eyes (9%) with a size 13.2 lens, respectively. In the V4c ICL group, 10 eyes (19%) were implanted with a size 11.5 lens, 27 eyes (50%) with a size 12.0 lens, and 17 eyes (31%) with a size 12.5 lens. In the market of South Korea, V4 and V4c ICL models are currently used to treat refractive errors, not the V4b ICL model. Both models showed comparable size profiles (V4, 11.5, vs V4c, 12.1; 12.0 vs 12.6; 12.5 vs 13.2; and 13.0 vs 13.7, respectively).
The inclusion criteria were patients older than 20 years of age who presented with myopia and with spherical equivalent preoperative refractions less than or equal to −18.00 D (range, −18.00 to −4.00 D). Exclusion criteria included previous ocular or intraocular surgery, ACD from the endothelium of less than 2.8 mm, corneal endothelial cell density of less than 2000 cells/mm 2 , cataract formation, opacification of the crystalline lens, evidence of acute or chronic corneal infection, inflammatory conditions of the cornea, history of glaucoma, amblyopia, retinal detachment, diabetic retinopathy, macular degeneration, or neuro-ophthalmic disease.
All patients received complete ophthalmic examinations, including manifested refractions; anterior segment evaluations by slit-lamp (Haag-Streit, Gartenstadtstrasse, Köniz, Switzerland); intraocular pressure measurements by a noncontact tonometer (NT-530; NCT Nidek, Aichi, Japan); keratometric measurements by autokeratometry (ARK-530A; NCT Nidek); and dilated fundus examinations. Central corneal thickness, axial length, anterior chamber volume, and horizontal white-to-white diameter were measured using ultrasound pachymetry, A-scans, a Pentacam (Oculus, Wetzlar, Germany), and Visante optical coherence tomography (OCT) calipers (Carl Zeiss Meditec, Jena, Germany), respectively.
In addition, 1-month postoperative measurements of the ACD (from the corneal endothelium to the crystalline lens surface) and pupil size under photopic and mesopic conditions were performed using a Visante OCT system. First, mesopic measurements were performed in a room luminance of 2 lux, which was monitored using a photometer (IL-1700 Radiometer; International Light, Newburyport, Massachusetts, USA). Second, after the light reflex was induced by shining a penlight into the contralateral eye, photopic measurements were performed. A 1-month postoperative vaulting assessment was performed using the Visante OCT system under photopic and mesopic conditions. Each measurement was performed 3 times by 1 physician, and the results were averaged.
A preoperative peripheral neodymium-yttrium-aluminum-garnet (Nd:YAG) laser iridectomy was performed at the 10:30 and 1:30 o’clock positions for all eyes in the V4 ICL implantation group but not for eyes in the V4c ICL implantation group. Sixty minutes before surgery, tropicamide and phenylephrine eyedrops were instilled. Five minutes before surgery, povidone-iodine 5% (Betadine; Alcon Laboratories, Fort Worth, Texas, USA) was applied. The surgical procedure was performed through a single-plane 3.0-3.2 mm superior corneal incision under topical anesthesia. The anterior chamber was filled with 1% sodium hyaluronate (Healon; Abbott Medical Optics, Santa Ana, California, USA), which was completely removed by manual irrigation and aspiration at the completion of surgery. The ICL was inserted with the use of an injector cartridge after the lens size was calculated by the STAAR Surgical Company after a horizontal white-to-white measurement. All surgeries were uneventful, and no definite intraoperative complications were observed. Postoperative topical medication included an antibiotic (Vigamox; Alcon) and dexamethasone 0.1% eyedrops every hour on the day of surgery, and then 5 times a day for 1 week. After 1 week, the dexamethasone 0.1% was replaced with fluorometholone 0.1%, and all eyedrops were prescribed 4 times daily for 1 month.
The results are expressed as the mean ± standard deviation. The Kolmogorov-Smirnov test was chosen to confirm the normal distribution of the data. For the comparison of eyes with V4c or V4 ICL implantation, independent t tests for continuous variables and χ 2 tests for categorical variables were performed. We applied the paired t test to compare postoperative vaulting, ACD and pupil size between photopic and mesopic conditions in each group. In addition, we used an independent t test to compare measurements between the groups under each lighting condition and changes in measurements according to differing lighting conditions between the groups.
The statistical analysis was performed using SAS software (v 9.2; SAS Institute, Cary, North Carolina, USA). Differences were considered statistically significant when P values were less than 0.05.
The preoperative and 1-month postoperative patient data are summarized in Table 1 . Postoperative vaulting, ACD, and pupil sizes of the eyes implanted with V4c and V4 ICLs under photopic and mesopic conditions are demonstrated in Table 2 .
|V4c ICL||V4 ICL|
|Age, years||25.09 ± 4.08 (20 to 33)||28.72 ± 6.21 (20 to 45)||<0.001|
|Sex (% women)||71.1||71.4||0.973|
|Laterality (% right eye)||53.6||51.9||0.857|
|Refractive errors (D)|
|Spherical||−8.80 ± 2.11 (−12.50 to −2.37)||−8.56 ± 2.29 (−15.62 to −3.75)||0.575|
|Cylindrical||−1.49 ± 0.77 (−3.75 to 0)||−1.50 ± 1.06 (−4.12 to 0)||0.953|
|Spherical equivalent||−9.54 ± 2.19 (−13.38 to −4.00)||−9.31 ± 2.33 (−15.87 to −4.31)||0.586|
|Flat K||42.99 ± 1.19 (40.25 to 44.75)||43.41 ± 1.43 (40.25 to 47.00)||0.098|
|Steep K||44.75 ± 1.24 (41.75 to 47.50)||45.13 ± 1.57 (41.25 to 48.50)||0.164|
|Mean K||43.87 ± 1.16 (41.00 to 45.50)||44.27 ± 1.45 (40.75 to 47.63)||0.116|
|Axial length (mm)||27.09 ± 1.10 (24.80 to 29.50)||26.84 ± 1.41 (24.43 to 30.54)||0.311|
|WTW diameter (mm)||11.38 ± 0.30 (10.86 to 12.04)||11.44 ± 0.34 (10.63 to 11.99)||0.397|
|Preoperative pupil size (mm)||6.92 ± 0.71 (4.30 to 8.30)||6.67 ± 0.64 (5.40 to 8.50)||0.053|
|Preoperative ACD (mm)||3.23 ± 0.19 (2.86 to 3.64)||3.21 ± 0.24 (2.86 to 3.85)||0.568|
|Preoperative IOP (mm Hg)||14.91 ± 2.38 (10 to 22)||14.15 ± 1.99 (10 to 20)||0.072|
|Preoperative CCT||509.75 ± 35.68 (416 to 595)||498.70 ± 33.81 (410 to 560)||0.099|
|Postoperative ACV||205.91 ± 22.72 (154 to 247)||197.04 ± 27.47 (138 to 260)||0.067|
|Characteristics||V4c ICL||V4 ICL|
|ICL Vaulting (μM)|
|Mean ± SD||399.5 ± 151.9||547.0 ± 173.1||428.3 ± 221.9||516.5 ± 223.7|
|Range||110 to 960||210 to 1060||60 to 1090||130 to 1230|
|Δ (Mean/SD/range)||147.5 ± 59.4 (60 to 370)||88.2 ± 54.9 (0 to 230)|
|Mean ± SD||3.16 ± 0.19||3.16 ± 0.19||3.14 ± 0.20||3.13 ± 0.21|
|Range||2.74 to 3.60||2.67 to 3.58||2.88 to 3.76||2.84 to 3.72|
|Δ (Mean/SD/range)||−0.001 ± 0.038 (−0.08 to 0.08)||−0.003 ± 0.049 (−0.10 to 0.14)|
|Pupil size (mm)|
|Mean ± SD||3.01 ± 0.55||5.33 ± 0.94||3.24 ± 0.72||5.44 ± 0.76|
|Range||2.12 to 4.32||2.97 to 7.02||2.08 to 5.25||3.35 to 6.89|
|Δ (Mean/SD/range)||2.32 ± 0.73 (0.43 to 3.88)||2.20 ± 0.72 (0.13 to 3.55)|