The Visian implantable collamer lens (ICL, STAAR Surgical Co.) is a posterior chamber phakic intraocular lens (pIOL); studies1–4 have shown its safety, predictability, and efficacy. Today, implantation of this pIOL is a common recommendation in patients who might not be good candidates for corneal refractive surgery.
The ICL design has continuously evolved with the goal of improving clinical outcomes and reducing the incidence of complications, mainly lens opacity and pupillary block.5,6 One modification is the central hole in the V4c model; the hole allows increased circulation of the natural aqueous humor. As a result, its implantation does not require a peripheral Nd:YAG iridotomy or surgical iridectomy, preventing the complications related to these procedures.7
Previous studies8,9 have shown that the presence of the central hole does not affect visual acuity or contrast sensitivity. However, some studies10,11 found a relationship between the presence of the central hole and photopic phenomena, such as ring-shaped dysphotopsia. These findings suggest that the presence of the central hole can negatively affect the quality of vision. Thus, the quality of life might also be affected under certain conditions, such as when viewing oncoming car headlights while driving at night. Nonetheless, these studies did not take into account the exact location of the central hole postoperatively.8–10
To our knowledge, only 2 studies have analyzed the effect of the location of the central hole on clinical and visual parameters.12,13 However, these studies did not analyze the exact ICL decentration based on Cartesian or polar coordinate systems or evaluate the influence of glare sources that might play a key role in visual disturbances when driving. Likewise, they did not assess the quality of vision and the related quality of life from the patient’s perspective.
The aim of the present study was to determine exact postoperative central hole location of the V4c ICL with respect to the pupil center and the visual axis (based on angle κ). Then, we evaluated the effect of the location on the quality of vision, including progressive headlight glare simulation under low mesopic conditions and the patient’s quality of life.
Patients and methods
This pilot interventional case series study was prospectively approved by the University Clinic Hospital Ethics Committee, Valladolid, Spain. The study was performed in compliance with the tenets of the Declaration of Helsinki, and all patients provided written informed consent.
This study included the far distance–dominant eyes of patients who had myopic posterior chamber V4c ICL implantation by the same experienced surgeon (M.J.M). The ICL power and size were determined according to the manufacturer’s recomendation using an online calculator.A The target was emmetropia.
Inclusion criteria were age 21 years or older, at least 6 months since ICL surgery, and a postoperative manifest spherical equivalent (SE) ranging from +0.50 diopter (D) to –0.50 D. Exclusion criteria included cataract, glaucoma, retinal anomalies, amblyopia, macular diseases, or a history of ocular surgery other than ICL implantation.
All tests were performed in both eyes. Outcomes in the dominant eye for distance were selected for statistical purposes because that eye tends to have priority in visual processing.14 Ocular dominance was detected by 3 successive trials using the hole-in-card test.14
All patients had a complete ophthalmologic examination. The evaluation included intraocular pressure (IOP)15 with the Ocular Response Analyzer (Reichert Technologies); objective central vault,16 defined as the narrowest perpendicular distance between the lens and the crystalline anterior capsule, measured with optical coherence tomography17 (3D-2000, Topcon Corp.); pupil diameter measurements (Wavelight Topolyzer Vario, Alcon Laboratories, Inc.), and visual acuity (Early Treatment Diabetic Retinopathy Study Chart, Precision Vision). The safety index and efficacy index were also calculated.
Central Hole Location
The central hole location of the pIOL was monocularly determined with respect to the visual axis. The contralateral eye was occluded during the measurement procedure. The measurement was performed in 3 steps.
First, the location of the center of the hole with respect to the pupil center was determined using slitlamp biomicroscopy (SL-8Z, Topcon Corp.). The patient was asked to open the eye and look straight ahead. A photograph was taken with a ×25 magnification under the illumination of a 5.0 mm wide parallelepiped. The x-coordinate and y-coordinate corresponding to the location of the center of the central hole with respect to the pupil center were measured in pixels using the caliper tool of IMAGEnet i-base software (version 3.17, Topcon Corp.); the measurements were later converted to millimeters.18 Regardless of the eye evaluated, nasal side displacement of the central hole along the x-axis was considered a positive value, while temporal side displacement was considered a negative value.
Second, the location of the visual axis with respect to the pupil center (ie, angle κ) was determined using a Galilei G4 dual Scheimpflug system (Ziemer Ophthalmic Systems AG). This device provides the distance in Cartesian coordinates (x, y) in millimeters. In addition, total corneal higher-order aberrations (HOAs) for a 6.0 mm pupil were obtained.
Finally, to calculate the actual displacement (in millimeters) of the central hole with respect to the pupil center or visual axis, values corresponding to x-coordinate and y-coordinate obtained with the dual Scheimpflug device were subtracted from those obtained on slitlamp biomicroscopy (Figure 1). In addition, the central hole location was determined using polar coordinates. Using the pupil center as a reference, the radius (r1 in Figure 1, B) was considered the total distance between the location of the pupil center (P in Figure 1) and the center of the central hole (H in Figure 1) by applying the Pythagorean theorem to the x-coordinate and y-coordinate. Using the visual axis as a reference, the radius (r3 in Figure 1, C) was considered the total distance between the location of the visual axis (V in Figure 1) and the center of the central hole. The polar angle with the pupil center reference was defined as the angle (p1 in Figure 1, B) between the central hole and pupil center, taking into account that the x-value and y-value for visual axis were both zero (ie, the pole) (Figure 1, B). With the visual axis reference, it was defined as the angle (p3 in Figure 1, C) between the central hole and visual axis, with both the x-value and y-value of pupil center axis being zero (Figure 1, C).
Progressive Headlight Glare Simulator
The mesopic contrast sensitivity was assessed with a progressive headlight glare simulation system (IOBA Halogen-Xenon Mesopic Contrast Sensitivity Test). The system consists of a room with no windows and walls covered with antiglare paper. A Pelli-Robson test was located 1 m from the seated patient. A 2 m high focal light pointing ahead was located 0.2 m behind the seated patient; this reproduced the ambient light of the driver’s car headlamps reflecting on the road. A headlamp was programmed to produce the intensity of a halogen or xenon car headlamp situated aside the Pelli-Robson chart (Precision Vision). The light intensity of the headlamp situated next to the Pelli-Robson chart was programmed to simulate the dynamic nature of an oncoming car’s headlight glare as experienced during nighttime driving.
The center of the Pelli-Robson chart was situated at 1.11 m height to simulate the average driver eyes’ height while driving.19 It was illuminated by a focal light simulating the illumination of the University of Michigan Transportation Research Institute European car light while driving at night.B Contrast sensitivity measurements were performed after 10 minutes of dark adaptation.20 Mesopic contrast sensitivity was measured under this illuminance. Then, to simulate the headlights of oncoming cars, patients viewed 5 seconds of progressively increasing intensity using the halogen and xenon algorithm. This illumination algorithm reproduces the scenario of an oncoming vehicle approaching from 100 to 40 m. The halogen glare contrast sensitivity and xenon glare contrast sensitivity were recorded. Finally, bothersome glare caused by halogen or xenon light was subjectively assessed using the de Boer rating scale, which ranges from 1 (unbearable) to 9 (unnoticeable) points.21
Quality of Life
Quality of life was quantified using the Quality of Life Impact of Refractive Correction (QIRC) questionnaire. The QIRC was developed and validated to assess the quality of life of people with a refraction correction, including those who had refractive surgery.22 This questionnaire consists of 20 items. The responses were automatically converted into a Rasch-weighted QIRC score on a scale of 0 to 100. The higher the score, the higher the quality of the patient’s life.22
A professional statistician (I.F.) performed the data analysis. The mean and standard deviation were calculated for normally distributed data. When data did not correspond to a normal distribution, the median and interquartile range (IQR) (value between the 25th percentile and 75th percentile of the distribution) were used. Comparisons of normally distributed preoperative data and postoperative data were performed using the paired student t test. The possible association between corneal total HOAs and central hole location or QIRC values was assessed using the Pearson correlation coefficient. The effect of the central hole location on quantitative variables (visual acuity, photostress recovery time, de Boer scale rating, QIRC questionnaire results) was analyzed using multiple linear regression models with the Cartesian coordinates (x, y) or polar coordinates (radius, polar angle) and postoperative time as independent variables.
Comparisons between postoperative contrast sensitivity variables (mesopic, halogen glare contrast sensitivity, and xenon glare contrast sensitivity) were performed using the Friedman test and paired analysis using the Wilcoxon test with the Bonferroni correction. Because of their low frequency, contrast sensitivity variables were transformed into dichotomous data and analyzed using logistic regression models. The mesopic contrast sensitivity values were grouped into 1.05 and lower log units and 1.05 and higher log units. Halogen glare contrast sensitivity values were grouped into 0.75 or lower log units and 0.75 or higher log units and xenon glare contrast sensitivity values, into 0.75 or lower log units and 0.75 or higher log units. Thus, odds ratio coefficients were obtained to estimate the likelihood of achieving higher contrast sensitivity values. Finally, the pupil diameter was included in the models to determine whether the pupillary aperture could affect the study parameters. Residual analysis was performed to check the assumptions of the regression models. The variance inflation factor was used to verify a lack of multicollinearity.
Two-sided P values less than 0.05 were considered statistically significant.
This study included 30 eyes of 30 patients. The mean age of the 22 women and 8 men was 32.4 ± 5.8 years. The mean postoperative follow-up was 19.9 ± 13.3 months (range 6 to 46 months). The mean manifest SE was −7.06 ± 4.04 D preoperatively and 0.00 ± 0.20 D postoperatively. The mean corrected distance visual acuity was −0.04 ± 0.05 logarithm of the minimum angle of resolution (logMAR) and −0.09 ± 0.07 logMAR, respectively. The mean postoperative uncorrected distance visual acuity was −0.08 ± 0.07 logMAR. The safety index was 1.13, and the efficacy index was 1.12. The mean Goldmann-correlated IOP was 15.5 ± 3.3 mm Hg preoperatively and 15.1 ± 2.2 mm Hg postoperatively, with no statistically significant differences (P = .52). The mean ICL vault was 428.1 ± 234.1 μm. The mean postoperative pupil diameter was 5.2 ± 1.0 mm. There was no association between total corneal HOAs and the central hole location (Table S1, available at http://jcrsjournal.org) or QIRC values (r = 0.20, P = .35). Similarly, the pupil diameter and postoperative time had no influence in any model or variable.
The mean decentration values of the central hole location in relation to the pupil center were as follows: x-coordinate, −0.24 ± 0.14 mm; y-coordinate, 0.11 ± 0.22 mm; radius, 0.34 ± 0.13 mm; polar angle, 154.37 ± 43.7 degrees (Figure 2, A). The mean decentration values of the central hole location in relation to the visual axis were as follows: x-coordinate, −0.33 ± 0.17 mm; y-coordinate, 0.21 ± 0.25 mm; radius, 0.47 ± 0.14 mm; polar angle, 151.55 ± 38.51 degrees (Figure 2, B).
Effect of Central Hole Location on Visual Acuity
The central hole location in relation to the pupil center and to the visual axis had no significant effect on the uncorrected distance visual acuity based on the Cartesian coordinates and polar coordinates (P ≥ .22) (Tables S2 to S4, available at http://jcrsjournal.org).
Effect of Central Hole Location on Progressive Headlight Glare Simulation
Contrast Sensitivity Measures
The median mesopic, halogen glare, and xenon glare contrast sensitivity values were 1.05 log units (IQR, 1.05 to 1.20), 1.05 log units (IQR, 0.75 to 1.05), and 0.75 log units (IQR, 0.75 to 1.05), respectively. The mesopic contrast sensitivity was statistically significantly higher than the halogen contrast sensitivity and xenon contrast sensitivity (both P < .001), and the halogen contrast sensitivity was statistically significantly higher than the xenon contrast sensitivity (P = .004).
Tables S2 to S4 (available at http://jcrsjournal.org) show the effect on contrast sensitivity of the central hole location with respect to the pupil center and visual axis analyzed using Cartesian and polar coordinates.
Contrast Sensitivity Photostress Recovery Time After Glare
The mean contrast sensitivity photostress recovery time was 1.44 ± 1.52 seconds (95% confidence interval [CI], 0.87-2.01) after halogen glare and 2.27 ± 1.80 seconds (95% CI, 1.60-2.95) after xenon glare. The difference between the 2 recovery times was statistically significant (P = .02). The regression models using the pupil center and the visual axis as a reference to locate the central hole with Cartesian and polar coordinates showed no significant effect on contrast sensitivity photostress recovery time after halogen or xenon glare (P ≥ .56 and P ≥ .60, respectively) (Tables S2 to S7, available at http://jcrsjournal.org). However, the x-coordinate value had a significant effect on contrast sensitivity photostress recovery time after xenon glare when Cartesian coordinates and the pupil center reference were used (β = 7.17; 95% CI, 2.89-11.44; P = .002) (Table S2, available at http://jcrsjournal.org).
De Boer Scale
The mean de Boer rating scale indicated significantly more discomfort with xenon glare (mean 4.83 ± 2.02 units; 95% CI, 4.08-5.59) than with halogen glare (mean 6.53 ± 2.27 units; 95% CI, 5.69-7.38) (P < .001). The regression models using the pupil center and visual axis as reference systems to locate the central hole and using Cartesian or polar coordinates showed no significant interaction on the de Boer scale for halogen glare or xenon glare (P ≥ .16 and P ≥ .62, respectively) (Tables S2 and S3, available at http://jcrsjournal.org). However, the radius distance had a significant effect on the de Boer halogen scale when polar coordinates were used as a reference system (β = −6.66; 95% CI, −12.91 to −0.41; P = .04).
Effect of Central Hole Location on Quality of Life
The mean QIRC score was 51.59 ± 5.88 points. The regression models performed using Cartesian and polar coordinates and the pupil center as the reference showed no significant effect on QIRC questionnaire values (P > .36). However, using Cartesian coordinates and the visual axis as reference, the y-coordinate of the central hole location had a significant effect on the QIRC outcomes (β = −9.34; 95% CI, −17.80 to −0.88; P = .03). When polar coordinates were used to locate the central hole, the polar angle had a significant effect on the QIRC score (β = 0.08; 95% CI, 0.02 to −0.14; P = .008) (Table S3, available at http://jcrsjournal.org).
The present study assessed the influence of the precise central hole location of the V4c ICL on the quality of vision; to our knowledge, ours is the first study of this topic. We found that a higher central hole location (positive y-values) in the vertical axis and a lower polar angle (upward decentration of central hole) using the visual axis as a reference system were related to worse quality of life as measured using the QIRC questionnaire. Patients’ subjective evaluation of whether the light after halogen glare was bothersome showed that the longer the radius (magnitude of central hole decentration), the more bothersome the light. In addition, the time to recover initial contrast sensitivity after xenon glare was longer when the central hole decentration was greater (positive values) in the x-axis and the pupil center was used as a reference system.
We found that the location of the central hole did not affect visual acuity, as other studies have reported. Park et al.13 assessed 3 groups according to the degree of ICL decentration (ie, within 1-, 2-, or 3-hole diameters from pupil center); they did not find significant variations between the groups. Pérez-Vives et al.12 performed an experimental study using a visual simulator and did not find any effect on visual acuity of 3 predetermined hole locations (centered, decentered 0.3 mm, and decentered 0.6 mm). Therefore, the central hole location does not appear to have a significant influence on visual acuity.
Other studies analyzed the effect of the central hole on the contrast sensitivity.9,23 Shimizu et al.9 did not find an effect under mesopic contrast sensitivity; however, they did not take into account the exact central hole location, as we did in the present study. Our study provides robust evidence regarding this issue because we evaluated patients under conditions simulating common progressive glare sources encountered during nighttime driving and considered the exact central hole decentration in each case.
Mesopic contrast sensitivity under glare conditions with the V4c ICL has also been studied. Shimizu et al.9 compared 2 ICL models (V4 versus V4c) and concluded that the presence of the central hole does not affect static mesopic contrast sensitivity. In the present study, we evaluated contrast sensitivity under progressive halogen and xenon intensity glare sources (similar to oncoming car headlamps) as well as photostress recovery time after glare and the degree to which glare was bothersome during simulated night driving. We found that progressive halogen and xenon glare sources further decreased contrast sensitivity values compared with that under mesopic conditions without glare. We also observed that the halogen glare source did not reduce contrast sensitivity as much as the xenon glare source. In addition, the photostress recovery time was shorter with halogen glare and patients reported that the glare was less bothersome than xenon glare. Our results can be explained by the fact that xenon illumination is more intense than halogen illumination, which makes driving at night more difficult,C a finding typically reported by night drivers.
We found no relationship between the location of the central hole and contrast sensitivity after exposure to halogen or xenon glare. Dysphotopsia phenomena have been reported after V4c ICL implantation.10,11 In an experimental study,10 the ICL hole produced an arc and ring images caused by light refraction from the inner surface of the central hole. This ring-shaped dysphotopsia might be related to the merging of arc images caused by obliquely incident light. Moreover, the radiant power of straylight is higher with an increasing angle of incidence of the incoming light rays. Therefore, this phenomenon might play an important role in glare scenarios. However, in our clinical study we located the light source to the left of the contrast sensitivity chart, simulating oncoming car headlights (oblique angle related to visual axis); we found no negative effect on contrast sensitivity values. Thus, our results suggested that this dysphotopsia phenomenon has no major clinical influence in terms of contrast sensitivity values after halogen or xenon glare, regardless of the central hole location.
Our QIRC results (mean 51.59 ± 5.88 points) were similar to those reported by Ieong et al.24 in patients with a no-hole ICL (mean 53.79 ± 5.60 points). However, we found lower quality-of-life values associated with upward central hole decentration along the vertical axis and to lower polar angle values with respect to the visual axis. Thus, based on our subjective (QIRC) outcomes, patients who had V4c ICL implantation and continue to report problems after the early postoperative period might benefit from repositioning the ICL slightly toward a lower vertical position in relation to the visual axis.
We found a significant relationship between total central hole decentration (radius) and de Boer scale values after halogen glare using the visual axis as the reference system. (The higher radius, the more bothersome the glare.) This finding was not observed when the pupil center was the reference. This finding might be attributed to the different central hole decentration values recorded for both reference systems (pupil center and visual axis). The distance from the central hole to the visual axis is greater than the distance from the central hole to the pupil center. In addition, greater central hole decentration in the x-coordinate was related to a longer photostress recovery after xenon glare when the pupil center was used as a reference. However, this was not true when the visual axis was used as a reference. These outcomes emphasize the importance of selecting a proper reference system because the systems (pupil center and visual axis) are not interchangeable.
The main limitation of the present study is that the outcomes are related to the sample population recruited, which means that they depend on the central hole decentration values in our patients. In addition, the magnitude of ICL decentration in our patients was not extremely large, as might be expected in usual clinical settings. Thus, future studies including ICL patients with larger decentration values and longer follow-ups are required. Another limitation is that the contrast sensitivity was assessed binocularly given that driving is a binocular activity; however, the central hole location was determined monocularly. To minimize this limitation, the dominant eye for distance was selected for determining the central hole location.14,25
In conclusion, our results further support that the V4c ICL with a central hole has an excellent efficacy and safety profile and that vision is not affected by the central hole location under mesopic conditions without glare sources. In addition, the location of the central hole did not affect contrast sensitivity with progressive halogen and xenon glare sources under mesopic conditions, as commonly occurs during nighttime driving. However, we also found that central hole location in the far distance–dominant eye matters because upward decentration can decrease the patient-perceived quality of life and a longer radius (magnitude of central hole decentration) can cause greater discomfort under halogen glare. Moreover, higher central hole decentration in the x-axis is likely to result in longer photostress recovery after xenon glare. Although experience tells us that most visual complaints are frequent and transient in the early postoperative period,26 ophthalmologists must continue to pay attention to these problems. Patient who continue to report such visual problems in the medium or long-term might be managed with discrete IOL centration if the central hole is decentered upward or nasally, in particular in the far distance–dominant eye.
What Was Known
- Implantation of a posterior phakic intraocular lens (pIOL) with a central hole is a safe, predictable, and effective option to correct moderate to high myopia in patients who are not suitable for corneal refractive surgery.
- The presence of the central hole in the posterior pIOL does not affect visual acuity or contrast sensitivity; however, experimental settings have shown that ring-shaped dysphotopsia might originate from light reflections off the IOL surface.
What This Paper Adds
- The central hole location of the posterior pIOL did not affect the visual acuity or contrast sensitivity with or without dynamic headlight glare sources. However, a decentered hole can decrease the quality of life and increase photostress recovery time and bothersome after glare.
- Surgeons should not place the posterior pIOL upward or nasally in cases in which achieving an exactly centered positioning is not possible.
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None of the authors has a financial or proprietary interest in any material or method mentioned.
Supplementary material available at www/jcrsjournal.org.
Other Cited Material
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