To investigate and compare vaulting and movement changes during accommodation in eyes with the V4c and V4 implantable collamer lenses (ICL).
Comparative, observational case series.
The medical records of 35 eyes (18 patients) with the V4 ICL and 51 eyes (26 patients) with the V4c ICL were retrospectively examined and included in analyses. Anterior chamber depth (ACD), posterior corneal surface–to–ICL distance (endo-ICL distance), pupil size, and postoperative vaulting were evaluated using the Visante anterior chamber optical coherence tomography system. Images were taken during the nonaccommodative and accommodative states 3 months after ICL implantation. Refractive error, keratometry values, axial length, intraocular pressure, and central corneal thickness were evaluated at 3 months postoperatively.
ICL vaulting did not significantly change during accommodation in eyes with either the V4 or V4c ICL ( P = .532 for V4 ICL and P = .415 for V4c ICL). However, significant reductions in ACD, endo-ICL distance, and pupil size were observed during accommodation in both groups. In eyes with a V4 ICL, the change in [Δ] ACD was 0.2 ± 0.1 mm ( P < .001), Δendo-ICL distance was 0.2 ± 0.1 mm ( P < .001), and Δpupil size was 0.5 ± 0.9 mm ( P = .021). For eyes with the V4c ICL, ΔACD was 0.2 ± 0.2 mm ( P < .001), Δendo-ICL distance was 0.2 ± 0.2 mm ( P < .001), and Δpupil size was 0.8 ± 1.2 mm ( P < .001). The mean reductions of each parameter were not statistically different between eyes with the V4 ICL and the V4c ICL.
Contrary to the light stimulation response, accommodation does not significantly affect ICL vaulting differently in eyes with either the V4 or V4C ICLs.
The implantable collamer lens (ICL) is a posterior chamber phakic intraocular lens that effectively corrects moderate to high myopia. Although ICL implantation offers outstanding benefits, postoperative complications have been reported by several investigators. Most adverse effects are associated with lens vaulting, defined as a change in the distance between the posterior surface of the ICL and the anterior surface of the crystalline lens. The development of secondary glaucoma and/or cataracts following ICL implantation is of significant concern. These complications can be more effectively anticipated and prevented by better understanding the effect of vaulting and its dynamic changes.
High vaulting conditions cause mechanical contact between the ICL and the iris, resulting in inflammation and increased intraocular pressure (IOP). Secondary glaucoma, pigment dispersion, iris atrophy, and metabolic cataract formation are also associated with high vaulting. Toward the other extreme, low vaulting conditions cause the ICL and crystalline lens to touch and the aqueous circulation in the perilenticular space to be inadequate. Mechanical contact and aqueous humor circulation impairment are thought to play a role in anterior subcapsular cataract development. Low vaulting also causes ICL decentration and tilt.
Measurements of ICL vaulting in the standard clinical setting have been traditionally carried out in predetermined mesopic lighting conditions without accommodation. Recently, the V4c Visian ICL (STAAR Surgical Company, Monrovia, California, USA) was designed with a 360 μm central hole to allow aqueous humor to flow without the need for an iridotomy. Clinically, the V4c ICL has shown comparable results to the conventional V4 ICL, which does not have a hole.
A recently published study compared vaulting between the V4c and V4 ICLs, but measurements were only made under mesopic lighting conditions with cycloplegia to avoid the potential influence of accommodation. However, vaulting unexpectedly and continuously changes with dynamic ICL movement and these changes are dependent on surrounding lighting conditions and the accommodative state of the eye. In our previous study, we compared the effect of lighting conditions on V4 and V4c ICL vaulting. We demonstrated that vaulting differences between photopic and mesopic lighting conditions are significantly larger in eyes with the V4c ICL than in those with the V4 ICL. Regarding accommodation, previous studies have indicated that accommodation-induced vaulting changes were not significant in eyes with a V4 ICL. However, it is possible in human eyes that, during accommodation, forward movement of the crystalline lens anterior pole and accompanying increases in lens thickness and zonular tension could affect vaulting in eyes with a V4c ICL.
In the present study, therefore, we examine and compare vaulting changes during accommodation in eyes with the V4c ICL and in eyes with the V4 ICL. Anterior chamber depth (ACD), posterior corneal surface–to–ICL (endo-ICL) distance, and pupil size are also examined.
This retrospective, comparative observational case series was performed with the approval of the Institutional Review Board of Yonsei University College of Medicine (Seoul, South Korea). All study conduct adhered to the tenets of the Declaration of Helsinki and followed good clinical practices. All patients provided written informed consent to allow their medical information to be included in study analyses.
Patients were included in analyses if they were older than 20 years of age and had myopia with a spherical equivalent (SE) between -4.00 and -18.00 diopters (D). All patients had undergone V4 or V4c ICL implantation in a standardized fashion by the same surgeon (D.S.Y.K.) at the Eyereum Eye Clinic (Seoul, South Korea) between August 1, 2013 and July 31, 2014. Patients were excluded from analyses if they had previous ocular or intraocular surgery (other than ICL implant), an ACD from the endothelium <2.8 mm, a corneal endothelial cell density <2000 cells/mm 2 , evidence of acute or chronic corneal infection, corneal inflammation, glaucoma, amblyopia, retinal detachment, diabetic retinopathy, macular degeneration, or neuro-ophthalmic disease.
Examinations and Measurements
All patients underwent complete ophthalmic examinations, which included manifest refraction, slit-lamp examination (Haag-Streit, Köniz, Switzerland), IOP measurement (noncontact tonometer, NT-530; NCT Nidek Co, Ltd, Aichi, Japan), autokeratometry (ARK-530A; NCT Nidek Co, Ltd), and dilated fundus examination. Central corneal thickness, axial length, and horizontal white-to-white distance were measured using ultrasound pachymetry, A-scan, and Visante optical coherence tomography (OCT) calipers (Carl Zeiss Meditec AG, Jena, Germany), respectively.
Three months following ICL implantation, central vaulting of the ICL over the crystalline lens, ACD (distance from corneal endothelium to crystalline lens surface), endo-ICL distance, and pupil size were measured in the nonaccommodative and accommodative states using the Visante OCT system. Central vaulting was designated as the distance between the anterior surface of the crystalline lens and the posterior surface of the ICL at the center of the ICL as shown in the Visante OCT image. Each measurement was performed 3 times by 1 physician and the average of the 3 measurements was used in analyses. A nonaccommodative state was attained by asking patients not to use visual display terminal (VDT) equipment (eg, cellular phone, tablet) or to read books or newspapers for at least 3 hours before examinations were performed. Measurements were taken while the patient fixated on a collimated light-emitting diode (focus at infinity) in a room with a luminance of 2 lux. Room light levels were monitored using a photometer (IL-1700 Radiometer; International Light, Newburyport, Massachusetts, USA). For measurements in the accommodative state, 1 eye was examined while the patient fixated with the nonexamined eye on a cross-shaped target placed 6 cm from the eye. Measurements were performed 3 times by 1 physician and the average of the 3 measurements was used in analyses.
A peripheral iridotomy was performed at the 10:30 and 1:30 clock positions using a neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser for eyes scheduled to receive the V4 ICL, as described in our previous study. Eyes planned for V4c ICL implantation were exempt from this procedure.
Sixty minutes before surgery, pupils were dilated with 0.5% phenylephrine and 0.5% tropicamide (Mydrin-P; Santen Pharmaceutical Co Ltd, Osaka, Japan). Povidone-iodine 5% (Betadine; Alcon Laboratories, Fort Worth, Texas, USA) was applied to the eye 5 minutes before surgery. 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 end of surgery. The ICL was inserted using an injector cartridge after the lens size was calculated by the STAAR Surgical Company. All surgeries were uneventful and no intraoperative complications were noted. The V4 and V4c ICL models have comparable size profiles (V4 vs V4c: 11.5 vs 12.1, 12.0 vs 12.6, 12.5 vs 13.2, and 13.0 vs 13.7).
Following surgery, a topical antibiotic (Vigamox; Alcon Laboratories) and corticosteroid (dexamethasone 0.1%) were used 4 times a day for 1 week. After the first week, dexamethasone 0.1% was replaced with fluorometholone 0.1% and all eye drops were continued 4 times a day for 1 month.
Results are expressed as mean ± standard deviation, where applicable. The Kolmogorov-Smirnov test was used to confirm data normality. To statistically compare data from eyes with V4 and V4c ICL implants, independent t tests were used for continuous variables and χ 2 tests or Fisher exact tests were used for categorical variables. Paired t tests were used to test differences between nonaccommodative and accommodative states in vaulting, ACD, endo-ICL distance, and pupil size. Independent t tests were used to compare these measurements between groups. All statistical analyses were performed using SAS software (version 9.2; SAS Institute, Inc, Cary, North Carolina, USA). Statistical significance was defined as P < .05.
A total of 86 eyes of 44 patients (32 women, 12 men) who underwent ICL implantation were ultimately included in analyses. All subjects were myopic and had a mean SE of −9.65 ± 2.42 D (range: −5.12 to −15.94 D). The V4 ICL was implanted into 35 eyes of 18 patients and the V4c ICL was implanted into 51 eyes of 26 patients. Table 1 summarizes patient demographic data and ocular characteristics before and 3 months after surgery. Mean ICL power was −13.0 ± 3.4 D (range, −7.0 to −22.0 D) in both groups. In the V4 ICL group, 4 eyes (11.4%) received an 11.5 lens, 21 eyes (60.0%) received a 12.0 lens, and 10 eyes (28.6%) received a 12.5 lens. In the V4c ICL group, 15 eyes (29.4%) received a 12.1 lens, 29 eyes (56.9%) received a 12.6 lens, and 7 eyes (13.7%) received a 13.2 lens.
|V4 ICL||V4c ICL|
|Age, y||29.7 ± 5.6 (22.0–45.0)||28.0 ± 4.7 (21.0–36.0)||.105|
|Sex (% women)||78%||69%||.739|
|Laterality (% right eye)||49%||49%||.959|
|Refractive errors (D)|
|Spherical||−9.49 ± 2.88 (−15.62 to −5.25)||−8.43 ± 2.01 (−14.75 to −4.25)||.060|
|Cylindrical||−1.53 ± 1.04 (−4.12 to 0)||−1.70 ± 0.67 (−3.50 to 0)||.378|
|Spherical equivalent||−10.26 ± 2.86 (−15.94 to −5.75)||−9.28 ± 2.05 (−15.63 to −5.12)||.084|
|Flat K||43.4 ± 1.0 (41.75–45.50)||43.1 ± 1.4 (40.3–46.3)||.271|
|Steep K||45.2 ± 1.5 (42.50–48.50)||45.0 ± 1.5 (41.8–48.8)||.524|
|Mean K||44.3 ± 1.2 (42.13–46.88)||44.0 ± 1.4 (41.0–47.5)||.378|
|Axial length (mm)||27.3 ± 1.6 (25.2–31.4)||26.9 ± 1.2 (23.8–30.6)||.279|
|WTW diameter (mm)||11.4 ± 0.3 (10.3–12.2)||11.3 ± 0.4 (10.5–12.0)||.141|
|Preoperative pupil size (mm)||6.7 ± 0.6 (5.5–7.4)||6.8 ± 0.6 (5.2–8.2)||.545|
|Preoperative ACD (mm)||3.3 ± 0.3 (2.9–3.9)||3.2 ± 0.2 (2.9–3.6)||.143|
|Preoperative IOP (mm Hg)||14.9 ± 2.8 (10–21)||14.5 ± 2.6 (10–20)||.534|
|Preoperative CCT (μm)||511.4 ± 32.4 (430.0–560.0)||512.4 ± 24.2 (460.0–560.0)||.874|
Postoperative vaulting, ACD, endo-ICL distance, and pupil size of eyes in the V4 and V4c ICL groups in both the nonaccommodative and accommodative states are provided in Table 2 . No significant differences in vaulting, ACD, endo-ICL distance, or pupil size were observed between V4 and V4c ICL–implanted eyes, regardless of accommodative state.
|Characteristics||V4 ICL||V4c ICL||P Value a||P Value b|
|ICL vaulting (μM)|
|Mean ± SD||547.1 ± 183.6||528.6 ± 229.3||582.0 ± 209.6||565.8 ± 237.5||.516||.551|
|Δ (mean/SD/range)||18.6 ± 133.8 (−210 to 350)||16.2 ± 132.2 (−260 to 330)||.947 c|
|Mean ± SD||3.2 ± 0.1||3.0 ± 0.2||3.2 ± 0.2||3.0 ± 0.3||.818||.228|
|Δ (mean/SD/range)||0.2 ± 0.1 (0–0.6)||0.2 ± 0.2 (−0.7 to 0.5)||.276 c|
|Endo-ICL distance (mm)|
|Mean ± SD||2.4 ± 0.3||2.2 ± 0.3||2.4 ± 0.2||2.2 ± 0.3||.896||.866|
|Δ (mean/SD/range)||0.2 ± 0.1 (0–0.5)||0.2 ± 0.2 (−0.3 to 0.8)||.607 c|
|Pupil size (mm)|
|Mean ± SD||5.5 ± 0.8||5.0 ± 1.2||5.4 ± 1.1||4.6 ± 1.3||.598||.168|
|Δ (mean/SD/range)||0.5 ± 0.9 (−0.8 to 3.0)||0.8 ± 1.2 (−1.7 to 3.3)||.278 c|
a P value between V4 ICL and V4c ICL in nonaccommodative state.
b P value between V4 ICL and V4c ICL in accommodative state.