Patients and Methods

The medical charts for 25 individuals (50 eyes) who underwent implantable collamer lens implantation (ICL V4 model) at Samsung Medical Center between October 2010 and December 2011 were retrospectively reviewed. The exclusion criteria included history of previous ocular surgery, anterior segment abnormality, and additional corneal ablation surgeries to correct excessive astigmatism or residual myopia, all of which could influence the presence of night vision disturbances. All patients included in the study were aged 18 years or older and in good general health. Institutional review board approval was obtained from the Samsung Medical Center Institutional Review Board, and all procedures adhered to the Declaration of Helsinki.

Comprehensive ocular examinations were performed before and after surgery, including uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) using a Snellen chart. Examinations also included manifest and cycloplegic refraction, slit-lamp biomicroscopy, noncontract tonometry, fundus examination, noncontact specular microscopy (SP-8000; Konan Medical, Inc, Nishinomiya, Hyogo, Japan), corneal topography (Orbscan IIz; Bausch & Lomb, Rochester, New York, USA), WaveScan imaging (Abbott Medical Optics, Santa Ana, California, USA), and ultrasound biomicroscopy (UBM) 835 (Carl Zeiss Meditec, Dublin, California, USA). UBM was performed to measure the horizontal sulcus-to-sulcus (STS) diameter preoperatively and to check implantable collamer lens vaulting postoperatively. UBM with a 50-MHz transducer and a fluid-filled eye cup was conducted under standard room lighting after instillation of proparacaine (Alcaine; Alcon, Fort Worth, Texas, USA). Pupil sizes were obtained preoperatively and postoperatively by WaveScan imaging under mesopic conditions with an illumination of 50 lux. Independent technicians performed the UBM, WaveScan, and Orbscan imaging.

Implantable collamer lens power calculations were performed with formulas provided by STAAR Surgical Co, based on keratometry, corneal thickness, anterior chamber depth with Orbscan, and cycloplegic refraction. We determined the implanted implantable collamer lens size based on the horizontal STS diameter acquired by UBM, which was described in our previous study.

Two peripheral iridotomies were performed using an argon and neodymium–yttrium-aluminum-garnet laser 2 weeks before surgery to prevent postoperative pupillary block. The iridotomies were located superiorly approximately 90 degrees apart. They were covered by the upper eyelid to avoid transillumination defects and to prevent light scattering.

Operations were performed by 2 skilled surgeons (E.S.C. and T.Y.C.) at Samsung Medical Center. Under topical anesthesia, a 3.0-mm temporal clear corneal incision was made with a diamond knife. Sodium hyaluronate 1.0% (Hyal 2000; LG Life Sciences, Seoul, South Korea) was injected into the anterior chamber, and the implantable collamer lens was inserted through the temporal incision with an injector (MicroSTAAR injector; STAAR Surgical Co). Toric implantable collamer lenses were implanted in eyes with a preoperative cylindrical power greater than 1.00 diopters (D) at the spectacle plane. If eyes had 0.50-1.00 D of astigmatism superiorly, we implanted a spherical implantable collamer lens and adopted a superior clear corneal incision in order to reduce astigmatism. Foot plates were tucked under the iris and on the ciliary sulcus using a modified intraocular spatula. Any remaining viscoelastic was irrigated out of the anterior chamber with a balanced salt solution. The corneal wound was self-sealed without any suturing. All of the surgeries were uneventful. Postoperative medication included topical antibiotics (Cravit; Santen, Japan) and steroids (Fluorometholone; Osaka, Santen) taken 4 times a day for up to 1 month.

The incidence and severity of night vision disturbances were evaluated using a questionnaire administered 6 months after surgery. Implantable collamer lens recipients were asked to evaluate their current night vision disturbances (glare and halo) using a 5-point scale (0 = no symptoms, 1 = minimal, 2 = mild, 3 = moderate, 4 = severe), which was adopted from a prior study. At the time of questionnaire administration, patients underwent postoperative ophthalmologic examinations as described above.

The possible risk factors for night vision disturbances that were evaluated included keratometric value, anterior chamber depth, postoperative residual refractive error, higher-order aberrations, preoperative and postoperative mesopic pupil size, the difference between preoperative and postoperative mesopic pupil size, the difference between mesopic pupil size and implantable collamer lens optic zone diameter, white-to-white (WTW) diameter, STS diameter, and postoperative implantable collamer lens vaulting. The power, size, optic zone diameter, and toricity of the implantable collamer lens were also assessed as possible risk factors.

Statistical analyses were performed using PASW 18.0 software (SPSS Inc, Chicago, Illinois, USA). A paired t test was used for the statistical comparison of preoperative and postoperative manifest refraction, aberrations, and pupil size. Univariate simple logistic regression analysis was used to examine the association between night vision disturbances and the aforementioned variables. Factors with a P value less than .1 were considered to be associated with night vision disturbances and included as candidates for multivariate analysis. Stepwise multiple logistic regression analysis was performed to evaluate meaningful risk factors affecting postoperative night vision disturbances. P values less than .05 were considered statistically significant.

Results

Patient baseline characteristics are listed in Table 1 . The mean patient age was 31.4 ± 8.3 years (range: 19-50 years). Nine patients (36.0%) were men and 16 (64.0%) were women. The mean implanted implantable collamer lens power and size was -14.4 ± 6.4 D (range: −7.0 to −24.0 D) and 12.1 ± 0.4 mm (range: 11.5-13.0 mm), respectively. The mean implantable collamer lens vaulting was 619.0 ± 215.4 μm (range: 252.5-1152.0 μm). A spherical equivalent (SE) of ±0.5 D was noted in 94% (47/50) of eyes and 74% (37/50) of eyes achieved UCVA ≥20/20. The mean SE improved significantly from −11.05 ± 4.56 D to −0.25 ± 0.66 D postoperatively ( P = .00). Among higher-order aberrations, trefoil increased significantly after surgery ( P = <.01) ( Table 2 ).

Pupil size was evaluated under mesopic conditions (50 lux) using WaveScan. The mean preoperative pupil size was 5.97 ± 0.93 mm (range: 3.25-7.0 mm), and the mean postoperative pupil size was 5.69 ± 0.68 mm (range: 3.0-6.75 mm). Pupil size decreased in 64% of eyes (32/50), increased in 20% (10/50), and was unchanged in 16% (8/50). Overall, mesopic pupil size was significantly decreased after surgery ( P = .01) ( Table 2 ).

Night vision disturbances were assessed by a questionnaire for each eye. Of all subjects, 34% (17/50) reported halos and 26% (13/50) reported glare. Of all questionnaire responses (2 per patient), 6% (3/50) reported more than a moderate degree of halos that caused difficulties in their lives.

We analyzed multiple preoperative and postoperative variables to determine if any were associated with postoperative night vision disturbances using univariate simple logistic regression. The possible determinants with a significance value P < .1 in univariate analysis were entered in the multiple logistic regression analysis. WTW and STS diameter, residual cylindrical power, postoperative spherical aberrations, size and optic zone diameter of implantable collamer lens, the difference between mesopic pupil size and implantable collamer lens optic zone diameter, and postoperative implantable collamer lens vaulting were summarized as potential risk factors for halos with P values less than .1 ( Table 3 ). Multicollinearity was found among implantable collamer lens size and WTW and STS diameter. Implantable collamer lens size and STS diameter were removed in the multivariable analysis. Table 4 shows the results of multiple logistic regression analysis. Halos were found to be significantly related to the difference between mesopic pupil size and implantable collamer lens optic zone diameter ( P = .013), as well as WTW ( P = .028) and implantable collamer lens optic zone diameter ( P = .030).

Table 4

Results of Multiple Logistic Regression Analysis for Halos After Implantable Collamer Lens Implantation

	B	SE	Wald	Df	Sig	Exp(B)	95% CI
Res cyl	−.820	.726	1.275	1	.259	.440	.106	1.828
ICL OZD	−4.005	1.846	4.708	1	.030	.018	.000	.679
Post SA	−6.853	6.017	1.297	1	.255	.001	.000	139.784
ICL vaulting	−.001	.002	.195	1	.658	.999	.995	1.003
Pupil_OZD	1.984	.797	6.204	1	.013	7.274	1.526	34.668
WTW	3.689	1.677	4.840	1	.028	40.014	1.496	1070.532
Constant	−24.207	16.159	2.244	1	.134	.000

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