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Clinical science
Visual quality comparison of conventional and Hole-Visian implantable collamer lens at different degrees of decentering
  1. Cari Pérez-Vives,
  2. Teresa Ferrer-Blasco,
  3. David Madrid-Costa,
  4. Santiago García-Lázaro,
  5. Robert Montés-Micó
  1. GIO, Optics Department, Faculty of Physics, University of Valencia, Valencia, Spain
  1. Correspondence to Dr Cari Pérez-Vives, Optics Department, University of Valencia, C/Dr Moliner 50, Valencia 46100, Spain; cari.perez{at}uv.es

Abstract

Purpose To compare the visual quality of implantable collamer lens (ICL) with and without central hole (Hole ICL and conventional ICL) at different degrees of decentering.

Methods An adaptive optics visual simulator (crx1, Imagine Eyes, Orsay, France) was used to simulate the –3, –6 and –12 dioptres (D) conventional and Hole ICLs in three conditions: centred and decentred 0.3 and 0.6 mm. Visual acuity (VA) at high-contrast, medium-contrast and low-contrast and contrast sensitivity (CS) were measured in 15 observers for 3 and 4.5 mm pupils.

Results No statistically significant differences in VA and CS were found between conventional and Hole ICLs for any ICL powers and pupil sizes evaluated (p>0.05). Regarding the effect of the ICL decentration on visual performance, we did not find statistically significant differences in VA and CS between centred, 0.3 and 0.6 mm decentred (p>0.05). Moreover, the ICL decentration affected the same manner on the conventional and Hole ICLs.

Conclusions The outcomes showed that conventional and Hole ICLs provided good and comparable visual performance for all powers and pupil sizes evaluated. Besides, ICL decentering affects the same manner both ICL models evaluated. The ICL decentering did not have any effect on the visual performance.

  • Optics and Refraction

https://doi.org/10.1136/bjophthalmol-2013-303787

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    Introduction

    The implantable collamer lens (ICL, STAAR Surgical, Nidau, Switzerland) is a posterior phakic intraocular lens implantation approved by the US Food and Drug Administration (FDA) for myopia correction. Several studies have shown the safety and effectiveness of the ICL to correct myopia,1 ,2 hyperopia3 ,4 and astigmatism.5 ,6 However, several complications have been reported.7 Complications include increased intraocular pressure,8 endothelial cells loss,9 pupillary block,10 pigment dispersion,11 glaucoma8 ,10 ,11 and anterior subcapsular cataract.12–15 Anterior subcapsular opacities result from surgical trauma or continuous ICL and crystalline lens contact because of insufficient vaulting.12–15 On the other hand, Fujisawa et al16 reported that another cause of secondary cataract formation may be the poor circulation of the aqueous humour that induces an ICL implantation.

    In order to reduce some complications and disadvantages, the ICL designs have undergone different improvements. The latest model is V4c Visian Implantable Collamer Lens, which has been designed with a central hole of 0.36 mm to improve the aqueous humour circulation17 and eliminates the need to perform neodymium:YAG (Nd:YAG) iridotomy or peripheral iridectomy before ICL implantation. Shiratani et al18 showed that an ICL with a hole of 1.0 mm in diameter in the centre of the optic did not degrade the performance of the ICL compared with the conventional version, and it is sufficient to increase the aqueous humour perfusion volume on the anterior surface of the crystalline lens, preventing cataract formation. Pérez-Vives et al19 compared the optical quality of conventional and Hole ICLs, measured in vitro, at different degrees of decentering. They found comparable optical quality between both designs of ICLs, without statistical differences between them. The effect of decentering equally affects both conventional and Hole ICLs. Shimizu et al20 ,21 evaluated the visual performance with the Hole ICL implanted. They showed that Hole ICL is a safe, effective, predictable and stable procedure to correct high to moderate myopia.

    The aim of the present study was to compare the visual performance provided by conventional ICL and Hole ICL for three powers (–3, –6 and –12 dioptres (D)) and evaluate the effect of decentering (0.3 and 0.6 mm) on the visual performance. For this purpose, we used an adaptive-optics system to simulate vision from the ICL's aberration pattern itself. Visual acuity (VA) for different contrast and contrast sensitivity (CS) were evaluated for 3 and 4.5 mm pupils.

    Materials and methods

    This study included 15 eyes of 15 individuals, aged 21–28 and having all experience in psychophysical experiments. Spherical refractive errors ranged between −1.50 and +0.25 D with astigmatism <0.25 D. They had all clear intraocular media and no known ocular pathology. Wavefront aberrations were measured with natural pupil. The pupil diameter was almost always larger than 4.5 mm, as the room's light was off during the experiments.

    The Visian ICL (STAAR Surgical) is a phakic lens made from Collamer, a flexible, hydrophilic and biocompatible material with a plate-haptic design and a central convex/concave optical zone. The ICL lenses are foldable, allowing for posterior chamber injection through a microscopic incision of 3.5 mm or smaller. When properly placed, the ICL should be positioned completely within the posterior chamber between the iris and crystalline lens with support on the ciliary sulcus. In this study, we have analysed the V4b and V4c ICL models for different powers: –3.00, –6.00 and –12.0 D for both models. The V4c model ICL introduces a central hole (diameter 0.36 mm) to increase the aqueous humour perfusion and reduce the risk of secondary cataract formation. The length of the ICLs was 12 mm, and the optical diameter was 5.5 mm in all cases.

    Adaptive-optics visual simulator

    We used the crx adaptive-optics system (Imagine Eyes, Orsay, France) comprising two basic elements: a wavefront sensor and a correcting device. The system optically conjugates the exit pupil plane of the individual with the correcting device, the wavefront sensor and an artificial pupil. The Shack–Hartmann wavefront sensor has a square array of 1024 lenslets. The wavefront aberration measurements are made at a wavelength of 850 nm. The deformable mirror is a correcting system made up of 52 independent magnetic actuators used either to partially or totally correct the aberrations up to the fifth order22 (18 Zernike coefficients) and to add different values of aberrations (up to fourth order). The deformable mirror's surface is controlled with a commercially available computer program (HASO, Imagine Eyes), which reshapes the deformable mirror from its normally flat surface to the desired shape. The observer viewed visual tests generated on a microdisplay through the adaptive optics system and an artificial pupil (figure 1). The microdisplay subtended a visual angle of 114×86 arcmin with a resolution of 800×600 pixels (pixel size=0.143 arcmin). The experiment's luminance conditions were manually adjustable.

    Figure 1
    Figure 1

    Schematic diagram of the crx1 system (Imagine Eyes, Orsay, France) used to measure and correct the eye's aberrations. It compromises two basic elements: the Shack– Hartmann wavefront sensor and the correcting device (deformable mirror) conjugated to the pupil plane. The visual test generated on a microdisplay was viewed through the deformable mirror and an artificial pupil. Access the article online to view this figure in colour.

    Experimental procedure

    The crx1 was programmed to measure and compensate for that particular eye's wavefront error up to the fifth order. In order to simulate in each individual the vision achieved after ICL implantation, the ICL's wavefront pattern was induced adding also the wavefront pattern of the myopic eye. The natural pupil diameter was monitored for each individual (≥4.5-mm), and the pupil size was controlled using the simulator's artificial pupil. The higher order aberrations (HOAs) of both models of ICLs were obtained from the study carried out by Pérez-Vives et al.19 They measured the HOAs and analysed the optical quality of ICLs with and without central hole at different degrees of decentering (centred and decentered 0.3 and 0.6 mm).

    Visual quality measurement

    High-contrast (100%), medium-contrast (50%) and low-contrast (10%) VA was measured using the Freiburg Visual Acuity Test software23 with a white background and luminance of 51 cd/m2. The acuity threshold was determined by the best-parameter estimation by sequential testing procedure24 based on 30 presentations. It was an eight-alternative, forced-choice method. The individual's task was to identify the Landolt-C gap position using a keypad. The VA value that was retained was the average of three measurements.

    The CS was measured for three spatial frequencies: 10, 20 and 25 cycles/degree (cpd). Oriented sinusoidal gratings (0°, 45°, 90° and 135°) were randomly generated and displayed on the microdisplay using a four-alternative, forced-choice method. A modified best-parameter estimation by sequential testing method based on 30 presentations was used to determine contrast thresholds.

    Data analysis

    The analysis of variance was used to disclose differences between both ICL models and different conditions of decentering. Posthoc multiple comparison testing was performed using the Holm–Sidak method. Differences were considered statistically significant when the p value was less than 0.05.

    Results

    Figures 2 and 3 show high-contrast, medium-contrast and low-contrast VA outcomes for –3, –6 and –12 D conventional and Hole ICLs for centred, 0.3 and 0.6 mm decentered positions at 3 and 4.5 mm pupils, respectively. We did not find statistically significant differences in VA values between conventional and Hole ICLs at any ICL powers, decentered position and for both pupils (p>0.05). Regarding the effect of decentering, no statistically significant differences were found between centred and decentered positions for any ICL powers and pupils evaluated (p>0.05).

    Figure 2
    Figure 2

    Visual acuity logMAR at high contrast (100%), medium contrast (50%) and low contrast (10%) for –3 (top left), –6 (top right) and –12 D (bottom left) of conventional and Hole implantable collamer lens at different degrees of decentering (legend, bottom right) at 3 mm pupil. Access the article online to view this figure in colour.

    Figure 3
    Figure 3

    Visual acuity logMAR at high contrast (100%), medium contrast (50%) and low contrast (10%) for –3 (top left), –6 (top right) and –12 D (bottom left) of conventional and Hole implantable collamer lens at different degrees of decentering (legend, bottom right) at 4.5 mm pupil. Access the article online to view this figure in colour.

    Figures 4 and 5 show the mean log10 CS values for –3, –6 and –12 D conventional and Hole ICLs for centred, 0.3 and 0.6 mm decentered positions at 3 and 4.5 mm pupils, respectively. No statistically significant differences were found in CS values between conventional and Hole ICLs at any refractive power, decentered positions and pupil sizes (p>0.05). In relation to the effect of decentering on both types of ICLs, we did not find statistically significant differences between centred and decentered positions for any ICL powers and pupils evaluated (p>0.05).

    Figure 4
    Figure 4

    Mean log contrast sensitivity plotted as a function of spatial frequency (10, 20 and 25 cycles/degree (cpd)) for –3 (top left), –6 (top right) and –12 D (bottom left) of conventional and Hole implantable collamer lens at different degrees of decentering (legend, bottom right) at 3 mm pupil. Access the article online to view this figure in colour.

    Figure 5
    Figure 5

    Mean log contrast sensitivity plotted as a function of spatial frequency (10, 20 and 25 cycles/degree (cpd)) for –3 (top left), –6 (top right) and –12 D (bottom left) of conventional and Hole implantable collamer lens at different degrees of decentering (legend, bottom right) at 4.5 mm pupil. Access the article online to view this figure in colour.

    Discussion

    The aim of the present study was to simulate and compare the vision provided by conventional and Hole ICLs at different refractive powers and at different degrees of decentering. This method allows us to evaluate and compare the patient's visual quality without the need of ICL implantation, analysing the effect of ICL model and ICL decentering effect.

    Effect of the hole on the optical quality

    VA values achieved with conventional and Hole ICLs at different degrees of decentering and for both pupils were good, obtaining values above 20/20 at high and medium contrast for all ICL powers. At low contrast, VA values were favourable too, about 20/30 for all powers of conventional and Hole ICLs, at different degrees of decentering and for both pupils. No statistically significant differences were found between conventional and Hole ICLs at any ICL power, any decentering position and both pupils (p>0.05; see figures 2 and 3). These outcomes agree with those obtained by Shimizu et al.20 They analysed the early outcomes of 20 eyes of 20 patients implanted with Hole ICL to correct moderate and high myopia (mean spherical equivalent −7.36±2.13 D). They found that the mean uncorrected VA was −0.20 logMAR and 100% of eyes had uncorrected VA of 20/20 or better 6 months after surgery.

    In terms of CS, for conventional and Hole ICLs, the CS function was good and comparable, and we did not find statistically significant differences between conventional and Hole ICLs at different degrees of decentering and both pupils (p>0.05; see figures 4 and 5). Shimizu et al21 compared postoperative visual performance after Hole ICL implantation in one eye and conventional ICL implantation in the other eye to correct moderate and high myopia (mean spherical equivalent −7.55±2.09 D). They evaluated the HOAs and photopic and mesopic CS function 3 months after surgery at 4 and 6 mm pupils. They concluded that after the Hole ICL implantation, the postoperative area under the log CS function was equivalent to that after conventional ICL implantation under photopic and mesopic conditions. Besides, Hole ICL implantation induced similar HOAs than conventional ICL implantation. This studio also agrees with our simulating outcomes that Hole ICL implantation provided similar outcomes in CS than conventional ICL implantation in real patients.

    Pérez-Vives et al19 measured the HOAs of conventional and Hole ICLs in vitro at different degrees of decentering for 3 and 4.5 mm pupil. They did not find statistically significant differences in any Zernike coefficient terms evaluated between conventional and Hole ICLs for any ICL powers and pupil sizes. Moreover, they also evaluated the point spread function (PSF) and simulated retinal images of ICLs calculated from the ICLs’ wavefront aberrations. They did not find differences in the PSF and simulated retinal images since both ICL models showed similar wavefront aberrations values without differences between them at any refractive power evaluated. These outcomes also show that the differences between both ICL models are minimal and clinically negligible.

    Effect of ICL decentering on the optical quality

    The effect of the ICL decentration on visual performance was also evaluated in the present study. We found that VA values at centred, 0.3 and 0.6 mm decentered were good and comparable for both pupils and all ICL powers, without statistically significant differences between them (p>0.05; see figures 2 and 3). Regarding the CS outcomes, the effect of decentering did not affect the CS values, and we did not find statistically significant differences in CS results between centred and decentered positions (p>0.05; figures 4 and 5). Moreover, ICL decentering affects the same manner both ICL models.

    Pérez-Vives et al19 found that ICL decentration induced coma aberration, which was greater when the ICL power and pupil size increased; statistically significant differences were found in coma aberration between centred and both degrees of decentering for all ICLs and pupils evaluated. However, they found the PSFs and simulated retinal images showed low influence of coma aberration increment, since they could not appreciate the visible differences between centred and decentered ICL positions. Therefore, they concluded that the increment of coma, due to the ICL decentering, was expected to not affect the visual quality of a patient implanted with the lens since these increments were less than 0.025 and 0.072 µm at 3 and 4.5 mm pupils. These changes in coma RMS values do not affect the visual performance.25 The present study confirms this fact; although the ICLs have been implanted in an eye, the coma increment when the ICL is decentered does not affect the visual performance.

    The visual simulator allows us to evaluate the impact of different IOLs and different conditions on visual performance before the surgical procedure takes place. However, we must take into account several limitations of our study, such as the surgery effects, ICL tilt or other postoperative complications,7 which may affect the outcomes reported here.

    In summary, the outcomes of the present study show that conventional and Hole ICLs provide good and comparable visual performance for all powers and pupils sizes evaluated. Moreover, ICL decentering affects the same manner both ICL models evaluated. The ICL decentering did not have any effect on the visual performance, like Pérez-Vives et al19 predicted in their study.

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    Footnotes

    • Contributors DM-C and RM-M made substantial contributions to conception and design. CP-V and TF-Bwere responsible for acquisition of data. SG-Lmade substantial contributions to analysis and interpretation of data. CP-V made substantial contributions of drafting the article. TF-B and DM-Cwere responsible for revising the article. RM-M gave the final approval of the version to be published.

    • Funding This research was supported in part by the research grant awarded by the Spanish Ministry of Science and Innovation to RM-M (#SAF2009-13342#) and a VALi+D research scholarship to CP-V (ACIF/2012/099, GeneralitatValenciana).

    • Competing interests None.

    • Patient consent Obtained.

    • Ethics approval Institutional Review Board at the University of Valencia-Research Group of Optometry.

    • Provenance and peer review Not commissioned; externally peer reviewed.