Purpose
To evaluate internal aberrometric profiles following phakic intraocular lens (PIOL) implantation.
Design
Retrospective and consecutive case series.
Methods
One hundred and five eyes of 65 patients were included. The optical aberrations were measured with the Topcon KR-1W aberrometer. Comparisons of internal aberrations for different models were made. Comparisons at 4 and 6 mm were made also within the same model for all the lenses. Comparisons regarding the implantation site were also performed: angle-supported (AS) anterior chamber (AC) (n = 47), iris-fixated (IF) (n = 27), and posterior chamber (PC) (n = 31).
Results
Root mean square (RMS) of internal optical higher-order aberrations (HOAs) changed significantly to higher values from 4-6 mm aperture diameter in each PIOL, as should be expected. However, this significant change was not detected in spherical aberration for Kelman Duet ( P = .753) and in trefoil for Acrysoft ( P = .059). Kelman lens showed significantly lower values of spherical aberration compared to Acrysoft at 4 mm ( P = .022) and at 6 mm ( P = .042). Acrysoft showed the lowest values at central zone for trefoil ( P = .043) and tetrafoil ( P = .002) in AC group. In the IF group, Artisan and Artiflex showed similar results for all internal aberrations. In the comparison between Visian Implantable Collamer Lens (ICL; STAAR Surgical Co, Monrovia, California, USA) and phakic refractive lens (PRL), both for posterior chamber, significantly lower values of coma were observed for ICL ( P = .033). IF lenses showed clinical evidence, but not significant, of better centering capability than AS lenses ( P = .096).
Conclusions
The study of intraocular aberrations is an adequate method to identify the clinical optical behavior and could help the surgeon to identify the most frequent problems related with each model.
Phakic intraocular lenses (PIOLs) are today an accepted alternative for the correction of high refractive errors. Three types of phakic intraocular lenses are currently used in clinical practice: (1) angle-supported lenses (AS); (2) iris-fixated lenses (IF); and (3) posterior chamber lenses (PC). Different PIOL models with different characteristics and specific complications have been designed.
Over the last decades, considerable attention has been given to the understanding of the physical optics of the eye and assessing the optical and visual quality after PIOL implantation, since photic phenomena and glare perception are still a concern in some patients.
The assessment of high-order wavefront aberration patterns may allow us to identify the diverse optical quality of PIOLs. The changes in the internal aberrometric profile induced by PIOLs might alter the visual performance of the patient. Previous studies have investigated this issue: a previous study analyzed the aberrometric pattern in myopic eyes implanted with a posterior chamber PIOL model lens (PRL) (Carl Zeiss/Meditec AG, Jena, Germany), reporting a slight reduction of third- and fourth-order aberrations for 5-mm pupils. Another recent study evaluating the aberrometric outcomes after Visian Implantable Collamer Lens (ICL; STAAR Surgical Co, Monrovia, California, USA) and AcrySof Cachet (Alcon Laboratories Inc, Fort Worth, Texas, USA) PIOL implantation showed fewer ocular high-order aberrations postoperatively.
Different PIOLs, with different designs, implanted at different anatomic locations may induce different changes in the aberrometric profile of the eye. If differences exist, the clinical study of the aberrations caused internally by these lenses may be relevant as it could lead to differences in the quality of vision after implantation. The aim of this study is to evaluate the aberrometric internal profile of different PIOL models so that surgeons may have a better understanding of their impact on visual acuity, thus enabling them to make comparisons.
Patients and Methods
This study included 105 eyes from 65 patients who underwent PIOL implantation at Vissum Corporation, Alicante, Spain. Each PIOL model was implanted using the specific protocol described for its implantation. The study followed the tenets of the Helsinki Declaration and all patients provided written informed consent to use the data obtained for scientific purposes. The study was approved by the Ethical Board Committee of Vissum Corporación Oftalmológica Alicante. For the purpose of the study, the PIOLs were divided into 3 main groups according to the site of implantation.
Group 1 included AS PIOLs: Baikoff ZB5M (Bausch & Lomb Surgical/Chiron Vision, Rochester, New York, USA) (n = 10 eyes), Kelman Duet (Tekia, Irvine, California, USA) (n = 14 eyes), AcrySof Cachet (Alcon Laboratories Inc, Fort Worth, Texas, USA) (n = 11 eyes), and ZSAL-4 (Morcher GmbH, Stuttgart, Germany) (n = 12 eyes). Group 2 included IF PIOLs: Artisan (Ophtec BV, Groningen, Netherlands) (n = 16 eyes) and Artiflex Veriflex (Abbott Medical Optic, Inc, Santa Ana, California, USA) (n = 15 eyes). Group 3 included PC PIOLs: Visian ICL (STAAR Surgical Co, Monrovia, California, USA) (n = 16 eyes) and PRL (Carl Zeiss/Meditec AG, Jena, Germany) (n = 11 eyes).
Materials, Patients, and Methods
This retrospective study comprised consecutive patients who had implantation of different models of PIOLs at different anatomic sites: 42 eyes (40%) belonged to male patients and 63 (60%) to female. Mean patient age was 38.34 ± 9.04 years (range, 23-55). The mean age for the AS group was 41.07 ± 8.71 years (range, 26-55): for Baikoff 48.80 ± 2.94, for Kelman 40.06 ± 6.96, for ZSAL 41.00 ± 7.51, and for Acrysof 32.09 ± 7.66. The mean age for the IF group was 35.35 ± 9.36 (range, 23-52): for Artisan 32.00 ± 11.46 and for Artiflex 36.81 ± 8.28. The mean age of PC PIOLs was 36.28 ± 8.18 (range, 25-51) years: for PRL 39.55 ± 6.15 and for ICL 35.71 ± 8.85. Spherical equivalent for the patients in the whole group was −12.60 ± 5.26 diopters (D) (range, −27.00 to −4.50). Spherical equivalent for AS lenses was −15.16 ± 5.82 D (range, −4.50 to −27.00): −13.83 ± 2.19 for AcrySof, −21.28 ± 4.09 for ZSAL, −13.36 ± 4.93 for Baikoff, and −12.59 ± 6.54 for Kelman. Spherical equivalent for IF lenses was −10.17 ± 3.65 D (range, −17.25 to −4.75): −13.38 ± 4.33 for Artisan and −11.32 ± 3.10 for Artiflex. Spherical equivalent for PC lenses was −10.57 ± 3.34 D (range, −16.63 to -5.00): −10.64 ± 4.62 for PRL and −10.51 ± 1.82 for ICL.
All groups were comparable in age ( P = .075, Kruskal-Wallis test), except Baikoff, with patients significantly older. Moreover, all groups were comparable in primary astigmatism ( P = .201, Kruskal-Wallis test) and in spherical equivalent ( P = .078, Kruskal-Wallis test), except ZSAL, used in patients with significantly higher ametropia.
Exclusion criteria were previous intraocular surgery, anterior chamber depth less than 3 mm, history of glaucoma or uveitis, crystalline lens opacity, scotopic pupil diameter more than 7 mm, ocular disease, or active retinal disease. At the moment of intervention all cases fulfilled the requirements for PIOL implantation.
All PIOLs included in the current study were evaluated under slit-lamp examination as properly centered for clinical purposes. All patients had best-corrected visual acuity of 20/20 and at least 20/25 of uncorrected vision. Other signs that could suggest decentration or tilt, such as severe halos and glare or abnormal retinoscopic pattern, were also considered as exclusion criteria.
Phakic Intraocular Lenses Included in This Investigation
The Baikoff (ZB, ZB5M, NuVita) PIOL is a rigid, polymethyl methacrylate (PMMA), Z-shaped, 5 mm optical zone AS lens similar to the Kelman 4-point-fixation multiflex implant. These models required a 5- to 6-mm-long incision for them to be implanted. Despite good anatomic and optical results, glare, halos, and pupil distortion prompted Baikoff to design a new lens called NuVita. The real optic diameter was increased to 4.5 mm and the total diameter to 5 mm. A new concave form was given to the posterior surface to increase the distance from the natural lens. The thickness of the edge was decreased by 20% to reduce potential peripheral contact on the corneal endothelium.
The Kelman Duet is a rigid, 2-part AS phakic PIOL. It has a 3-point angle-support PMMA haptic angulated from 11.1 to 9.6 degrees, a foldable silicone optic 6 mm in diameter, and overall lengths from 12-13 mm. It can be implanted through a 2-mm incision: first the haptic and then the optic. The main advantage of this model is the exchangeability of the lens haptic and optic.
The ZSAL-4 Plus is a rigid, 4-point-fixation PMMA lens with a diameter of 5.5 mm and an effective optic zone of 5 mm. The optic has a flat anterior and concave posterior surface and the overall lengths vary from 12.5-13 mm. The haptic geometry has been changed to a thinner connecting bridge between the optic and the first footplate and a thicker connecting bridge between both footplates to increase haptic flexibility and disperse compression forces against angle structures. The angulation of the haptics is 19 degrees, reduced compared to previous models to obtain less contact between the lens and the endothelium.
The AcrySof Cachet PIOL is a single-piece, AS, foldable, all-soft acrylic and hydrophobic lens. It has a 6.0-mm meniscus optic and can be inserted through a 2.6-mm incision. The overall length varies from 12.5-14 mm. It is available from -6.00 D to -16.5 D in half-diopter increments. Its optic is connected to 2 flexible haptic arms by the bridge on either side. The haptics are designed to allow the compression within the angle for IOL stability, without creating the excessive force that could cause angle tissue damage or pupil ovalization.
The Artisan IF lens is a 1-piece all-PMMA lens with a convex-concave optic. Since 1999, the Artisan lens has also been available for astigmatism correction and is a concave-convex lens. The total length is 8.5 mm with an optic diameter up to 6 mm. The 2 diametrically opposed haptics attach the lens to the mid-peripheral, virtually immobile iris stroma, allowing a relatively unrestricted movement of the iris. The Artisan myopia PIOL ranges from −3.00 to −15.5 D, while the Artisan hyperopia PIOL ranges from +1 to +12 D (increments of 0.5 D).
The Artiflex Veriflex PIOL has a flexible, 3-piece design and consists of a 6.0-mm convex-concave silicone optic of ultraviolet-filtering polysiloxane and rigid haptics of compression-molded PMMA; its overall length is 8.5 mm. It ranges from −2.00 to −14.5 D (increments of 0.5 D). The toric Artiflex is also available in spherical power from −2.00 D to −14.50 D and cylinder powers from 1.00 D to 5.00 D.
The Visian ICL is a single-piece plate lens made of an elastic collamer, which is a copolymer of poly-hydroxyethylmethacrylate and porcine collagen with a high light transmittance. It is also highly biocompatible and permeable to gas and metabolites. It is foldable and can be implanted through a 2.8-mm corneal incision in the sulcus. The optic diameter varies between 4.65 and 5.50 mm and the refractive index is 1.45. The toric model is available in cylindrical powers up to 6.0 D. Different degrees of night visual disturbance have been reported by ICL patients (6.1%). Under mesopic condition, the edges of the lenses might cause high-order aberrations.
The PRL (Phakic Refractive Lens) is a monofocal and biconcave (myopia) and convex-concave (hyperopia) spherical, single-piece plate lens made of pure silicone, with a refractive index of 1.46. It is elastic and hydrophobic, and it requires a 3.2-mm incision for implantation. It has spherical, thin, and flexible haptics and has no anatomic fixation sites. Its edges lie on the zonular fibers and float in the PC, maintaining a space between the implant and the anterior capsule of the lens. It has an optic diameter from 4.5-5.0 mm. The specific gravity is 0.99. Myopic implants come in 2 lengths (11.3 and 10.8 mm) and range in power from −3.00 to −20.00 D. The hyperopic implant is 10.6 mm long and ranges from +3.0 to +15.0 D. Both are available in 0.5-D increments.
Wavefront Analysis
The wavefront aberration data were obtained with the KR-1W aberrometer (Topcon Corp, Tokyo, Japan) under pharmacologically induced pupillary dilation (tropicamide). At least 3 measurements were obtained for 4- and 6-mm pupil diameters. Its software can calculate and reconstruct the internal wavefront by subtracting ocular and corneal wavefront data. Its repeatibility in high-order aberration measures has been reported.
The KR-1W is based on the Hartmann-Shack wavefront sensor in which Zernike polynomial expansions up to fourth radial order are calculated for a 4- and 6-mm pupil. The following parameters of internal ocular wavefronts were recorded: high-order aberration (HOA) root mean square (RMS), third-order RMS, fourth-order RMS, primary coma RMS (computed for the Zernike terms Z ± 13), trefoil RMS (computed for the Zernike terms Z ± 33), secondary astigmatism RMS (computed for the Zernike terms Z ± 24), tetrafoil RMS (computed for the Zernike terms Z ± 44), and the primary spherical aberration with its sign (Zernike coefficient Z04). All RMS were expressed in micrometers.
Statistical Analysis
For the treatment of the data, SPSS version 19.0 for Windows (SPSS, Chicago, Illinois, USA) was used. Normality of the samples was studied with the Kolmogorov-Smirnov test and homoscedasticity with the Levene test. For the comparison of several independent samples, the Kruskal-Wallis test was used. For the comparison of 2 independent samples the Mann-Whitney test was used and for the comparison of 2 related samples the Wilcoxon test was used. The level of statistical significance was ( P < .05).
Results
Intraocular Aberrations in Angle-Supported Phakic Intraocular Lenses
Results for AS PIOLs are shown in Table 1 and Figures 1 and 2 . The comparison of aberrations at 4 mm with aberrations at 6 mm revealed, as expected, an increase in all the aberrations regardless of the kind or order of the considered aberrations. As is well known, the aberrations increase at the peripheral zone of any optical device. However, one of the most interesting points of this analysis was, in our opinion, to quantify this increment in PIOLs. A remarkable result was obtained regarding the spherical aberration for the Kelman model: no significant change was detected comparing the values obtained at 4 and 6 mm ( P = .814, Wilcoxon test). The comparison of trefoil at 4 and 6 mm for AcrySof also showed that there were no statistical differences ( P = .059, Wilcoxon test).
| Internal Aberrations | Intraocular Aberrations Root Mean Square (μm) for Angle-Supported Lenses | Comparison Among Angle-Supported Lenses ( P Value) | |||
|---|---|---|---|---|---|
| Kelman | AcrySof | Zsal | Baikoff | ||
| High-order aberrations | |||||
| 4 mm | 0.1154 ± 0.0272 | 0.1327 ± 0.0374 | 0.1590 ± 0.0509 | 0.1790 ± 0.095 | .091 |
| 6 mm | 0.8415 ± 0.4966 | 0.5455 ± 0.1378 | .150 | ||
| P value for 4- with 6-mm comparison (same lens) | .001 | .003 | |||
| Third | |||||
| 4 mm | 0.0931 ± 0.0304 | 0.0945 ± 0.0388 | 0.1270 ± 0.0514 | 0.1510 ± 0.0880 | .154 |
| 6 mm | 0.5569 ± 0.3525 | 0.3009 ± 0.1433 | .063 | ||
| P value for 4- with 6-mm comparison (same lens) | .001 | <.001 | |||
| Fourth | |||||
| 4 mm | 0.0631 ± 0.0218 | 0.0882 ± 0.0325 | 0.0900 ± 0.0258 | 0.0970 ± 0.0645 | .118 |
| 6 mm | 0.4608 ± 0.2507 | 0.3518 ± 0.1396 | .303 | ||
| P value for 4- with 6-mm comparison (same lens) | .001 | .003 | |||
| Trefoil | |||||
| 4 mm | 0.0546 ± 0.0270 | 0.0545 ± 0.0321 | 0.0780 ± 0.0308 | 0.0890 ± 0.0354 | .043 |
| 6 mm | 0.2885 ± 0.2618 | 0.1373 ± 0.1121 | .072 | ||
| P value for 4- with 6-mm comparison (same lens) | .001 | .059 | |||
| Coma | |||||
| 4 mm | 0.0715 ± 0.0318 | 0.0745 ± 0.0305 | 0.0920 ± 0.0594 | 0.1010 ± 0.0872 | .928 |
| 6 mm | 0.4338 ± 0.3144 | 0.2500 ± 0.1328 | .167 | ||
| P value for 4- with 6-mm comparison (same lens) | .001 | .004 | |||
| Tetrafoil | |||||
| 4 mm | 0.0323 ± 0.0136 | 0.0215 ± 0.0142 | 0.0440 ± 0.0222 | 0.0410 ± 0.0242 | .002 |
| 6 mm | 0.2685 ± 0.1965 | 0.1364 ± 0.1051 | .072 | ||
| P value for 4- with 6-mm comparison (same lens) | .002 | .005 | |||
| Secondary astigmatism | |||||
| 4 mm | 0.0131 ± 0.0095 | 0.0182 ± 0.0154 | 0.0240 ± 0.0158 | 0.0400 ± 0.0271 | .027 |
| 6 mm | 0.2292 ± 0.1743 | 0.1200 ± 0.0871 | .093 | ||
| P value for 4- with 6-mm comparison (same lens) | .001 | .005 | |||
| Spherical (Z 4 0 ) | |||||
| 4 mm | −0.0385 ± 0.0372 | −0.0791 ± 0.0409 | −0.0580 ± 0.0501 | −0.0420 ± 0.0590 | .148 |
| 6 mm | −0.0392 ± 0.2574 | −0.2527 ± 0.1813 | .042 | ||
| P value for 4- with 6-mm comparison (same lens) | .814 | .004 | |||
Regarding the comparison of different AS PIOLs at 4 mm, no statistical differences were found for spherical aberration in the group as a whole ( P = .148, Kruskal-Wallis test). However, there was a statistically significant difference between Kelman and Acrysof ( P = .022 Mann-Whitney test). No particular differences at 4 mm were detected in the one-to-one comparison of Kelman with the other AS lenses. Differences were also detected within the AS group at 4 mm for other aberrations: trefoil ( P = .043) and tetrafoil ( P = .002). AcrySof obtained the lowest values for both aberrations. The comparison at 6 mm for different AS lenses was only performed for those PIOLs with a 6 mm optical zone, Kelman and AcrySof, and also revealed statistically significant differences ( P = .041). In both cases (at 4 and 6 mm) the spherical aberration was significantly higher for AcrySof.
Intraocular Aberrations in Iris-Fixated Phakic Intraocular Lenses
Results for IF PIOLs are shown in Table 2 and Figures 3 and 4 . Very similar results were found for Artisan and Artiflex. In fact, no significant differences were found between these 2 lenses when comparing the aberrations at 4 and 6 mm of the optical zone. When comparing at 4 and 6 mm for each lens, significant differences were found for all aberrations except for internal astigmatism ( P = .463 for Artisan and P = .083 for Artiflex, Wilcoxon test).
| Internal Aberrations | Intraocular Aberrations Root Mean Square (μm) for Iris-Fixated Lenses | Comparison Between Iris-Fixated Lenses ( P Value) | |
|---|---|---|---|
| Artisan | Artiflex | ||
| High-order aberrations | |||
| 4 mm | 0.1186 ± 0.0410 | 0.1344 ± 0.0462 | .492 |
| 6 mm | 0.5514 ± 0.2381 | 0.6306 ± 0.2904 | .579 |
| P value for 4- with 6-mm comparison (same lens) | .018 | <.001 | |
| Third | |||
| 4 mm | 0.0829 ± 0.0281 | 0.1119 ± 0.0426 | .089 |
| 6 mm | 0.3329 ± 0.1980 | 0.3044 ± 0.1070 | .922 |
| P value for 4- with 6-mm comparison (same lens) | .018 | <.001 | |
| Fourth | |||
| 4 mm | 0.0814 ± 0.0344 | 0.0831 ± 0.0294 | .820 |
| 6 mm | 0.3100 ± 0.1702 | 0.3831 ± 0.1523 | .341 |
| P value for 4- with 6-mm comparison (same lens) | .018 | <.001 | |
| Trefoil | |||
| 4 mm | 0.0500 ± 0.0311 | 0.0569 ± 0.0332 | .871 |
| 6 mm | 0.2129 ± 0.1288 | 0.2044 ± 0.1599 | .820 |
| P value for 4- with 6-mm comparison (same lens) | .028 | .001 | |
| Coma | |||
| 4 mm | 0.0586 ± 0.0323 | 0.0800 ± 0.0456 | .376 |
| 6 mm | 0.2314 ± 0.1952 | 0.2481 ± 0.1373 | .579 |
| P value for 4- with 6-mm comparison (same lens) | .028 | .001 | |
| Tetrafoil | |||
| 4 mm | 0.0286 ± 0.0168 | 0.0288 ± 0.0213 | .922 |
| 6 mm | 0.1214 ± 0.0682 | 0.1813 ± 0.1196 | .413 |
| P value for 4- with 6-mm comparison (same lens) | .018 | .001 | |
| Secondary astigmatism | |||
| 4 mm | 0.0214 ± 0.0186 | 0.0344 ± 0.0216 | .222 |
| 6 mm | 0.1771 ± 0.1404 | 0.1400 ± 0.0913 | .535 |
| P value for 4- with 6-mm comparison (same lens) | .018 | <.001 | |
| Spherical (Z 4 0 ) | |||
| 4 mm | −0.0586 ± 0.0508 | −0.0606 ± 0.0334 | .840 |
| 6 mm | −0.2900 ± 0.3831 | −0.2019 ± 0.2144 | .894 |
| P value for 4- with 6-mm comparison (same lens) | .176 | .021 | |
