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Performance of the 1CU accommodating intraocular lens in relation to capsulorhexis size

Vargas, Luis G. MD; Auffarth, Gerd U. MD; Becker, Klio A. MD; Rabsilber, Tanja M. MD; Holzer, Mike P. MD

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Journal of Cataract & Refractive Surgery: February 2005 - Volume 31 - Issue 2 - p 363-368
doi: 10.1016/j.jcrs.2004.02.071
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Accommodation is the ability of the eye to increase its refractive power to produce a clearer image at near. Helmholtz1 showed that the classic mechanism of accommodation is achieved by contraction of the ciliary muscle. This releases the circumferential tension on the zonules, increasing the anterior–posterior lens surface curvature and thus the dioptric power. Glasser and Kaufman2 confirmed this theory using ultrasound biomicroscopy and goniovideography. Contraction of the ciliary muscle also causes the pars plana and crystalline lens to move forward. The loss of accommodative amplitude (presbyopia) usually occurs after 40 years of age.

The development of accommodating intraocular lenses (IOLs) holds promise for the correction of presbyopia.3,4 One theory of how these IOLs work is that the ciliary body directly causes forward vaulting of the IOL. Under this theory, the ciliary body presses on the lens or contraction of the ciliary muscle generates a pressure gradient between the aqueous and vitreous, causing anterior displacement of the lens–zonule diaphragm and steepening of anterior central lens curvature. Under these terms, we can define pseudophakic accommodation as the refractive change in the pseudophakic eye caused by interactions between the contracting ciliary muscle and the zonule–capsule–IOL complex, resulting in a change in refraction at near fixation.

The 1CU (HumanOptics AG) is a single-piece, hydrophilic acrylic accommodating IOL. It has an optic diameter of 5.5 mm and 4 soft haptics with a hinge located at the optic–haptic junction to facilitate forward movement of the optic. Preliminary studies of forward shifting of the 1CU IOL induces a certain degree of accommodation. Auffarth et al.5 found a potential accommodative effect with this IOL design in the laboratory. In their study, the IOL optic moved anteriorly after circular force was applied to the sclera by creating a circular bend at the level of the ciliary body and after viscoelastic material was injected into the vitreous. The shift of focus was confirmed with a reading target. In another study,6 the same group reported good distance visual acuity (mean 0.76 ± 0.23) and near visual acuity (mean 0.40 ± 0.23) in 25 patients after implantation of the 1CU IOL; there were no complications associated with the IOL or surgical procedure.

To achieve accommodation, accommodating IOLs must preserve the integrity of the lens capsule, zonules, and ciliary muscle. There are no reports in the peer-reviewed literature of a relationship between capsulorhexis overlap of the IOL optic or capsulorhexis centration and the performance of accommodating IOLs. However, studies show that a continuous curvilinear capsulorhexis (CCC) that is smaller than the IOL optic, thus overlapping the entire optic edge area, prevents posterior capsule opacification (PCO) better than a larger, decentered CCC.7,8

The purpose of this study was to determine whether CCC size, measured by the amount of overlap between the CCC and IOL optic, and CCC centration affect the performance of the 1CU accommodating IOL.

Patients and Methods

The medical records of 34 patients (43 eyes) who had phacoemulsification and implantation of the 1CU IOL between January 1, 2001, and November 1, 2002, were retrospectively analyzed. Patients with previous eye pathology or intraocular surgery were excluded from having implantation of an accommodating IOL.

All surgeries were performed using a standard phacoemulsification technique consisting of topical anesthesia of lidocaine 2% gel, 2 paracenteses (1.2 mm, nasal and temporal), a superior clear corneal incision (2.80 mm × 1.75 mm) made with a disposable knife, and a CCC with a diameter between 4.0 mm and 5.5 mm created under viscoelastic material. In situ fracture of the nucleus, or a hybrid technique in eyes with a hard nucleus, and quadrant removal under high flow and high vacuum were performed. Irrigation/aspiration of cortex using a bimanual technique and capsule polishing were successfully achieved in all cases. The IOL was implanted using the injector recommended by the manufacturer after the clear corneal incision was enlarged to 3.0 mm. The viscoelastic material was completely removed at the end of the procedure. No sutures were used in any case. Postoperative medications consisted of a mixture of neomycin sulfate, polymyxin sulfate, and dexamethasone 4 times a day for 3 weeks.

The uncorrected and best corrected near and distance visual acuities were measured preoperatively and postoperatively and the distance corrected near visual acuity, postoperatively.

Three months after surgery, standardized retroillumination photographs were taken with a Haag-Streit BC 900 slitlamp with EyeCap SL software for Digital Imaging (Haag-Streit Wedel Deutschland). The photographs were digitized and imported into the Evaluation of Posterior Capsule Opacification (EPCO) computerized image-analysis system for quantification of PCO.8,9 The retroillumination photographs and camera settings have been described in detail.9 In brief, several images of the IOL are taken. The flashlight reflex is slightly decentered on the IOL's optic edge, and pictures with reflexes on the right and left side are taken. If reflexes on the photographs interfere with the analysis, the images can be imported into the EPCO merge subprogram, where clear portions are used to create a composite reflex-free image.

Figure 1 shows the steps used to obtain the patient's CCC–optic overlap score. Using the EPCO program, the desired area of evaluation (IOL's optic circumference) is marked. Next, the computer mouse is used to draw and outline the CCC, enabling assessment and quantification of the area between the optic's edge and the CCC margin over 360 degrees. The measurement of this area gives the amount of overlap between the CCC and the IOL optic, which is graded from 0% to 100%. A high score means that a large portion of CCC covers the anterior surface of the optic and that the CCC is relatively small; a small amount of overlap means a larger CCC and that less of the CCC covers the optic.

Figure 1.
Figure 1.:
A: Slitlamp photographs are taken to assess the amount of CCC–optic overlap and the size and centration of the CCC. B. Retroillumination photographs are taken and imported into EPCO. C: The IOL's optic is marked. D: The CCC is outlined and highlighted (blue). E: The highlighted area is used to calculate the amount of CCC–optic overlap from 0 to 1 (0% to 100%). F: A view of the final screen image used to evaluate the amount of CCC–IOL overlap, which in this case is 32.5%.

Statistical analysis was performed using SPSS 11.0 for Windows (SPSS Inc.). A P value of 0.01 or less was considered statistically significant.

Results

Nineteen eyes completed the 3-month follow-up and were included the analysis. The mean age of the patients was 53.5 years (range 30 to 73 years). The mean preoperative best corrected near acuity was 0.30 (range counting fingers to 0.6).

Postoperatively, the mean uncorrected distance acuity was 0.70 (range 0.30 to 1.00) and the mean best corrected distance acuity, 0.94 (range 0.80 to 1.00). The mean distance corrected near acuity was 0.50 (range 0.10 to 1.00), which improved to 0.90 (range 0.30 to 1.00) with correction. The mean uncorrected near acuity was 0.60 (range 0.10 to 1.00).

The mean CCC diameter was 4.3 mm (range 3.7 to 5.0 mm). The mean amount of CCC decentration was 0.35 mm (range 0 to 0.50 mm) and of CCC–optic overlap, 35% (range 16% to 56%).

There was a negative correlation between the amount of CCC–optic overlap and postoperative distance corrected near acuity (r=0.641, Pearson; P=.003). Eyes with a greater amount of overlap and thus a smaller CCC (n=9, Figure 2) had worse distance corrected near acuity than eyes with a smaller amount of overlap (larger CCC) (n=10, Figure 3) (mean 0.62 ± 0.20 and 0.42 ± 0.20, respectively) (Table 1). There was no correlation between uncorrected near acuity and CCC decentration or between postoperative uncorrected and best corrected distance acuities and CCC overlap and decentration. Figure 4 shows the uncorrected and best corrected distance and near acuities and the amount of CCC–optic overlap.

Figure 2.
Figure 2.:
Eyes with a CCC–optic overlap of more than 35% and thus the worst distance corrected near acuity. A and B: An eye with an overlap of 45.5% and a distance corrected near acuity of 0.40 (20/50). C and D. An eye with an overlap of 55.2% and a distance corrected near acuity of 0.20 (20/100).
Figure 3.
Figure 3.:
Eyes with a CCC–optic overlap of less than 35% and thus the best distance corrected near acuity. A and B: An eye with an overlap of 16.1% and a distance corrected near acuity of 0.70 (20/30). C and D. An eye with an overlap of 0.336 and a distance corrected near acuity of 0.63 (20/32).
Table 1
Table 1:
Correlation between age, visual acuity, and CCC and the IOL optic–CCC overlap.
Figure 4.
Figure 4.:
Uncorrected and best corrected distance and near acuities and the amount of CCC–optic overlap.

Decentration of the CCC had no effect on the visual outcome. Figure 5 shows visual acuities distributed by the amount of CCC decentration (<0.35 mm and ≥0.35 mm).

Figure 5.
Figure 5.:
Correlation between visual acuity and amount of CCC decentration.

Discussion

The 1CU IOL has shown potential accommodative capabilities in laboratory and clinical settings.3–6,10,11 The extent and strength of accommodative power is difficult to predict individually and may be related to many factors such as age and the anatomical integrity of the zonules, capsule, and ciliary body. This study confirmed the ICU IOL's accommodating properties, and the visual outcomes are similar to those in previous studies.

Langenbucher et al.11 compared patients with a 1CU IOL and an age-matched group with a poly-(methyl methacrylate), hydrophilic acrylic, or hydrophobic acrylic IOL. They found the 1CU group had better distance corrected near acuity than the monofocal group (mean 0.32 ± 0.11 and 0.14 ± 0.10, respectively) and better accommodation amplitude measured with the PowerRefractor (mean 1.00 ± 0.44 diopter [D] and 0.35 ± 0.26 D, respectively), retinoscopy (mean 0.99 ± 0.48 D and 0.24 ± 0.21 D, respectively), subjective near point (mean 1.60 ± 0.55 D and 0.42 ± 0.25 D, respectively), and defocusing (mean 1.46 ± 0.53 D and 0.55 ± 0.33 D, respectively). In a study by Hayashi and coauthors,12 near visual acuity in pseudophakic eyes with monofocal IOLs ranged between 0.05 and 0.13 depending on the age of the patient. We found better near visual acuity (distance corrected near acuity 0.50), especially in cases when the CCC–optic overlap was less than 35%.

Previous studies emphasize the importance of an intact CCC and in-the-bag IOL placement in achieving pseudoaccommodation. However, there are no reports of what CCC size and amount of CCC–optic overlap are adequate to improve outcomes. In a previous study,8 we found that an overlap of 30% is sufficient for PCO prevention but that an overlap of less than 20% significantly increases the risk for PCO formation.

An unexpected finding in our study was that distance corrected near acuity was better in eyes with a CCC–optic overlap of less than 35% than in eyes in which the amount of overlap was greater. This suggests that the ideal amount of overlap is between 25% and 35%, which corresponds to a 4.5 to 5.0 mm CCC that is centered. A smaller CCC (greater overlap) can increase the risk for anterior capsule fibrosis, which can lead to phimosis of the CCC opening and, as in our study, worse near visual acuity. A larger CCC (small amount of overlap) can increase the risk for CCC decentration and PCO.7,13

Nishi and Nishi14 refilled the lens capsule in monkey eyes with injectable silicone compounds. The accommodation amplitude attained, which was a small fraction of the value before surgery, may be sufficient for near vision after cataract surgery to achieve emmetropia. This agrees with an earlier study by Nishi and coauthors15 and might be the result of decreased capsule pliability caused by capsule fibrosis. Other experimental studies16,17 found that capsule opacification gradually reduces the accommodation amplitude obtained after endocapsular phacoemulsification through a buttonhole CCC and capsule refilling. Although our results seem to confirm this theory, the number of eyes evaluated was small and the follow-up too short to draw a definite conclusion. Nevertheless, there is a similar tendency with the 1CU design. Distance corrected near acuity was better when the CCC–optic overlap was less than 35%. More clinical studies are required to confirm whether these findings apply to other accommodating IOL designs because different biomaterials and designs can change the behavior of the capsular bag during the healing process. It has been shown that silicone and plate-haptic IOLs lead to higher rates of anterior capsule opacification and capsule fibrosis than hydrophilic acrylic IOLs.18,19

In summary, we report early visual results in eyes with a 1CU accommodating IOL. The IOL gave adequate uncorrected and best corrected distance acuity, similar to the visual results obtained with conventional monofocal IOLs. However, the uncorrected and distance corrected near acuities were better than the acuities in studies of monofocal IOLs. This was enhanced when the CCC overlapped the IOL's optic by less than 35%, thus giving better near visual acuities without compromising distance vision. There was no correlation between CCC decentration and visual results (far or near). More clinical studies are required to confirm the findings of this study. We propose that a centered CCC that overlaps the IOL optic by 25% to 35% can optimize the outcomes in eyes with a 1CU accommodating IOL.

References

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© 2005 by Lippincott Williams & Wilkins, Inc.