Risk Factors Associated With Night Vision Disturbances After Phakic Intraocular Lens Implantation




Purpose


To investigate the incidence and severity of night vision disturbances after implantable collamer lens surgery and to analyze the risk factors.


Design


Retrospective, noncomparative study.


Methods


Medical charts from 50 eyes of 25 patients who underwent implantable collamer lens implantation were retrospectively reviewed. The incidence and severity of night vision disturbances were evaluated using questionnaires administered 6 months after surgery. Univariate simple and multiple logistic regression analyses were used to detect risk factors associated with postoperative night vision disturbances. Potential risk factors included in the analysis were 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 diameter, sulcus-to-sulcus diameter, and postoperative implantable collamer lens vaulting. The power, size, optic zone diameter, and toricity of the implantable collamer lens were also included as variables.


Results


The incidence of night vision disturbances was 34.0% for halos and 26.0% for glare. Halos were found to be significantly related to the difference between mesopic pupil size and implantable collamer lens optic zone diameter ( P = .013), white-to-white diameter of the cornea ( P = .028), and implantable collamer lens optic zone diameter ( P = .030). For glare, toricity of the implantable collamer lens was revealed as a significant risk factor ( P = .047).


Conclusions


Although not severe, the incidence of night vision disturbances after implantable collamer lens implantation was not negligible. Possible risk factors for night vision disturbances include implantable collamer lens optic zone diameter, the difference between mesopic pupil size and implantable collamer lens optic zone diameter, and white-to-white diameter of the cornea for causing halos, and the toricity of the implantable collamer lens for causing glare.


Phakic intraocular lens (IOL) implantation is a well-known refractive surgery, along with photorefractive keratectomy (PRK), laser-assisted subepithelial keratomileusis (LASEK), and laser in situ keratomileusis (LASIK). Implantable collamer lenses (Visian ICLs; STAAR Surgical, Nidau, Switzerland) are sulcus-placed posterior chamber phakic intraocular lenses. They are particularly important for patients with a thin cornea or a high level of myopia. These patients are not ideal candidates for corneal refractive surgery. Implantable collamer lens implantation has been accepted as a safe and effective surgical procedure with low risk of chronic anterior chamber inflammation, iris atrophy, and endothelial cell damage when compared with anterior chamber iris-fixed phakic intraocular lenses.


Postoperative night vision disturbances are a major factor in causing decreased visual satisfaction after refractive surgery. Halos are bright circles that appear to surround a light source, such as oncoming car headlights. Glare consists of difficulties seeing in the presence of bright light, such as car headlights at night. Several studies have been conducted about night vision disturbances after corneal refractive surgery. A few studies reported that implantable collamer lens implantation is superior to LASIK in terms of visual outcomes, including visual quality. However, no prior reports have focused on postoperative night vision disturbances after implantable collamer lens implantation.


Herein, we report the incidence and severity of night vision disturbances after implantable collamer lens implantation and analyze the risk factors associated with night vision disturbances.


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 ).



Table 1

Demographics of Patients Who Underwent Implantable Collamer Lens Implantation




































Parameter Mean ± SD Range
Age (y) 31.4 ± 8.3 19-50
Sex (% female) 64.0
Laterality (% right eye) 50.0
ICL power (diopters) −14.4 ± 6.4 −7.0 to −24.0
ICL size (mm) 12.1 ± 0.4 11.5-13.0
ICL vault (μm) 619.0 ± 215.4 252.5-1152.0
Toric ICL (%) 38

ICL = implantable collamer lens.


Table 2

Preoperative and Postoperative Outcomes in Eyes That Underwent Implantable Collamer Lens Implantation



















































Parameters Mean ± SD
Preoperative Postoperative P Value (Paired t Test)
Spherical equivalent (diopters) −11.05 ± 4.56 −0.25 ± 0.66 <.01
Aberrations (μm)
Total RMS 9.63 ± 4.70 1.42 ± 0.71 <.01
Higher-order RMS 0.38 ± 0.16 0.43 ± 0.17 .11
Coma 0.23 ± 0.16 0.26 ± 0.23 .44
Trefoil 0.16 ± 0.10 0.31 ± 0.24 <.01
Spherical aberration 0.06 ± 0.17 0.00 ± 0.25 .15
Mesopic pupil size (mm) 5.97 ± 0.93 5.69 ± 0.68 .01

RMS = root mean square.


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 3

Potential Risk Factors for Postoperative Night Vision Disturbances After Implantable Collamer Lens Implantation a





































































































































































































































Halos Glare
Exp(B) Sig Exp(B) Sig
Age 1.054 .156 0.985 .705
Keratometric value
Flat K 0.906 .614 0.915 .673
Steep K 0.855 .385 1.088 .670
Mean K 0.868 .470 1.004 .986
Sim K 0.798 .500 1.658 .147
Anterior chamber depth (mm) 2.680 .278 3.144 .232
Sulcus-to-sulcus diameter (mm) 3.373 .087 0.891 .871
White-to-white diameter (mm) 6.613 .034 0.421 .342
Residual refractive errors (diopters)
Spherical 0.819 .695 0.796 .668
Cylindrical 0.282 .026 0.428 .113
Spherical equivalent 0.512 .184 0.610 .278
Pupil size (mm)
Preoperative 1.424 .339 0.807 .518
Postoperative 0.871 .751 0.411 .082
Postoperative – preoperative 2.125 .124 1.609 .336
Preoperative aberrations (μm)
Total RMS 0.957 .504 1.037 .618
Higher-order RMS 0.839 .635 0.876 .681
Coma 0.711 .860 4.307 .450
Trefoil 25.873 .313 3.838 .699
Spherical aberration 10.442 .317 0.242 .631
Postoperative aberrations (μm)
Total RMS 1.258 .587 1.309 .548
Higher-order RMS 0.880 .942 0.102 .304
Coma 0.497 .630 0.720 .829
Trefoil 0.087 .165 2.612 .451
Spherical aberration 0.003 .098 1.393 .834
ICL power (diopters) 0.983 .729 0.973 .647
ICL size (mm) 13.795 .010 0.955 .958
ICL optic zone diameter (mm) 0.058 .008 0.906 .919
Toric ICL 1.778 .346 0.214 .065
Toricity of the ICL 1.089 .621 0.357 .072
Pupil – ICL optic zone diameter (mm) 2.999 .053 0.311 .092
Postoperative ICL vaulting (μm) 1.003 .043 0.997 .087

Exp(B) = odds; ICL = implantable collamer lens; K = keratometric value; RMS = root mean square; Sig = significance ( P value).

a Univariate simple logistic regression analysis.



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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Jan 9, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Risk Factors Associated With Night Vision Disturbances After Phakic Intraocular Lens Implantation

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