Journal of Refractive Surgery

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Potentially Accommodating Intraocular Lenses - An In Vitro and In Vivo Study Using Three-dimensional High-frequency Ultrasound

Oliver Stachs, PhD; Hanka Schneider, MD; Joachim Stave, PhD; Rudolf Guthoff, MD

Abstract

ABSTRACT

PURPOSE: To investigate the accommodative performance of new intraocular lenses (IOLs) using the advantages of three-dimensional ultrasound biomicroscopy.

METHODS: An in vitro simulation device was designed to study IOL performance using an artificial capsular bag and a stretching device. The haptic region of the Akkommodative 1CU (HumanOptics AG) and CrystaLens AT-45 (Eyeonics Inc) was visualized in vitro in three dimensions, using an in-house developed three-dimensional ultrasound biomicroscope. The in vitro results were used to describe the in vivo situation in four patients with accommodative implants.

RESULTS: The haptic position and angulation in consideration of the accommodation state was distinguished and analyzed. In the simulation model, a maximal angulation change of 4.5° and 4.3° and a maximal forward shift of 0.33 mm and 0.28 mm was observed for the AT-45 and 1CU, respectively. In vivo, a change in haptic angulation <10° and a maximal forward shift of 0.50 mm was observed For the 1CU. These changes correspond to a theoretical approximate value of 0.50 diopters.

CONCLUSIONS: The in vitro simulation device examined with three-dimensional ultrasound biomicroscopy provided information on the accommodative performance of these potentially accommodative IOL designs. Using three-dimensional ultrasound biomicroscopy, corresponding changes in haptic angulation during pharmacological-induced accommodation were observed. [J Refract Surg. 2005;21:37-45.]

Abstract

ABSTRACT

PURPOSE: To investigate the accommodative performance of new intraocular lenses (IOLs) using the advantages of three-dimensional ultrasound biomicroscopy.

METHODS: An in vitro simulation device was designed to study IOL performance using an artificial capsular bag and a stretching device. The haptic region of the Akkommodative 1CU (HumanOptics AG) and CrystaLens AT-45 (Eyeonics Inc) was visualized in vitro in three dimensions, using an in-house developed three-dimensional ultrasound biomicroscope. The in vitro results were used to describe the in vivo situation in four patients with accommodative implants.

RESULTS: The haptic position and angulation in consideration of the accommodation state was distinguished and analyzed. In the simulation model, a maximal angulation change of 4.5° and 4.3° and a maximal forward shift of 0.33 mm and 0.28 mm was observed for the AT-45 and 1CU, respectively. In vivo, a change in haptic angulation <10° and a maximal forward shift of 0.50 mm was observed For the 1CU. These changes correspond to a theoretical approximate value of 0.50 diopters.

CONCLUSIONS: The in vitro simulation device examined with three-dimensional ultrasound biomicroscopy provided information on the accommodative performance of these potentially accommodative IOL designs. Using three-dimensional ultrasound biomicroscopy, corresponding changes in haptic angulation during pharmacological-induced accommodation were observed. [J Refract Surg. 2005;21:37-45.]

An intraocular lens (IOL) is implanted in the capsular bag during cataract surgery. Capsular fibrosis and I capsular bag shrinkage result in a hardening of the IOL haptic and optic in the capsule. Despite excellent restoration of visual acuity and biocompatibility, no accommodation is present in Pseudophakie eyes, as the IOL optic does not change in shape or position. Pseudophakie accommodation could potentially be achieved by ciliary muscle action if the hard lens cortex and nucleus were replaced by a flexible material. Several authors16 reported refilled lens capsules in animal experiments.

To date, Pseudophakie accommodation has only been achieved by multifocal IOLs and by an axial shift of the IOL optic. This shift of the IOL optic occurs when the ciliary muscle contracts and induces a change in haptic configuration. Recently, several attempts using different designs712 have been made to achieve Pseudophakie accommodation. The fundamental idea of all approaches to achieve potentially accommodating IOLs is to allow an axial displacement of the IOL optic.

Quantification of the axial IOL movement induced by accommodation in humans has been performed with ultrasound81315 and by using dual-beam partial coherence interferometry.1619 High-frequency ultrasound20,21 is the only tool available to visualize the IOL haptic geometry hidden behind the iris diaphragm. High-frequency sonographic image analysis becomes difficult if information from only one plane is available. The aim of this study is the evaluation of haptic geometry based on a three-dimensional reconstruction of single section, ultrasound biomicroscopic data sets.

Table

TABLE 1Intraocular Lens PropertiesFigure 1. Photograph and three-dimensional ultrasound biomicroscopy image and B-scan of the ICU in the artificial silicone capsular bag (CB). The optic (0) and haptic (H) are well differentiated. The spot (*) in the equatorial region of the capsular bag is caused by the haptic ridge of the I0L, whereas this point is not always present under different scanning directions. The point (#) acts as the fulcrum and is used as the center of rotation for angulation determination. The echo pattern of the posterior convex side of the haptic is a falsified image due to time-delay effects. Abbreviations: O = optic, # = fulcrum, H = haptic, and * = haptic ridge.

TABLE 1

Intraocular Lens Properties

Figure 1. Photograph and three-dimensional ultrasound biomicroscopy image and B-scan of the ICU in the artificial silicone capsular bag (CB). The optic (0) and haptic (H) are well differentiated. The spot (*) in the equatorial region of the capsular bag is caused by the haptic ridge of the I0L, whereas this point is not always present under different scanning directions. The point (#) acts as the fulcrum and is used as the center of rotation for angulation determination. The echo pattern of the posterior convex side of the haptic is a falsified image due to time-delay effects. Abbreviations: O = optic, # = fulcrum, H = haptic, and * = haptic ridge.

To simulate accommodation, a test chamber using an artificial capsular bag and a stretching device was developed. The haptic regions of the Akkommodative ICU (HumanOptics AG, Erlangen, Germany) and the CrystaLens AT-45 (Eyeonics Ine, Aliso Viejo, Calif) were scanned in the simulation model during different accommodative (stretched) states. These in vitro results were correlated and used to describe the in vivo condition in four patients with accommodative implants.

MATERIALS AND METHODS

The IOLs studied and their properties are shown in Table 1 and are depicted as insets in Figures 1 and 2. The IOLs were implanted in a silicone capsular bag to allow simulation of the accommodation process. The artificial capsular bag is shown in Figure 3. Its characteristics have been described in detail22 and the main properties are summarized in Table 2.

An in-house developed three-dimensional ultrasound biomicroscope was used to evaluate IOL placement and haptic configuration in the capsular bag. The principle of the ultrasound biomicroscope has been described in detail.21 lezzi et al23 and Cusumano et al24 described a technique for three-dimensional ultrasound biomicroscopy, and its application has been demonstrated.25,26 For this study, three-dimensional imaging was accomplished using a standard ultrasound biomicroscope (Model 840; Humphrey Instruments, Carl Zeiss Group, Jena, Germany) extended such that precise movement of the B-scan plane in the z-direction could be obtained. This principle for three-dimensional imaging has been summarized in detail.27 In this arrangement, three-dimensional data sets consisting of parallel B-scans spaced at defined distances apart could be obtained.

Figure 2. Photograph and three-dimensional ultrasound biomicroscopy image and B-scan of the CrystaLens AT-45 in the artificial silicone capsular bag (CB). The fulcrum is marked (#). The optic (O) and haptic (H) are well differentiated, whereas the echo pattern (*) is caused by the polyimide construction of the AT-45 plate haptic. Abbreviations: 0 = optic, # = fulcrum, H = haptic, and * = polyimide construction.Figure 3. A, B) Artificial capsular bag and C) stretching device for accommodation simulation. The rotation of the inner ring with pins (marked in C) shifts the arms and stretches or relaxes the bag to simulate the force effects of the ciliary muscle. The ICU I0L is implanted.

Figure 2. Photograph and three-dimensional ultrasound biomicroscopy image and B-scan of the CrystaLens AT-45 in the artificial silicone capsular bag (CB). The fulcrum is marked (#). The optic (O) and haptic (H) are well differentiated, whereas the echo pattern (*) is caused by the polyimide construction of the AT-45 plate haptic. Abbreviations: 0 = optic, # = fulcrum, H = haptic, and * = polyimide construction.

Figure 3. A, B) Artificial capsular bag and C) stretching device for accommodation simulation. The rotation of the inner ring with pins (marked in C) shifts the arms and stretches or relaxes the bag to simulate the force effects of the ciliary muscle. The ICU I0L is implanted.

The three-dimensional reconstruction was performed using Voxel View (Vital Images, Fairfield, Iowa) and Amira (TGS, San Diego, Calif) software. These commercial software packages provide an interactive environment allowing spatial orientation of individual planes, construction of three-dimensional perspectives, segmentation, and determination of distances and surfaces. Building three-dimensional constructs allows outlining of anatomic structures in space and can be used for volume measurements. For evaluation of haptic configurations and axial changes in IOL position, additional software, ImageJ (NIH, Bethesda, Md) and TINA (Raytest, Straubenhardt, Germany), was used.

Table

TABLE 2Properties of the In Vitro Capsular Bag Model

TABLE 2

Properties of the In Vitro Capsular Bag Model

For analysis of the IOL performance, the artificial capsular bag was mounted in a simulation device (see Fig 3C). The arms of the fixture clamp the bag around its periphery at eight points. Rotation of the inner ring stretches or relaxes the bag. Inner ring rotation is accomplished by a stepping motor driving a worm gear. The amount of stretching correlates with the rotation of the inner ring. The entire arrangement is submerged in water for sonographic imaging. In vitro, no movement artifacts exist, and a high-quality three-dimensional reconstruction can be performed (160 individual B-scans with 440X440 pixel). The three-dimensional volume was used to identify the tangential plane of the IOL respectively haptic, and an oblique reconstruction is possible to perform the biometric measurements. Thus, in vitro, an effect of tilting on the results of the biometrie measurements can be excluded. For angulation determination, the center of rotation was placed at the fulcrum (see Figs 1 and 2) and the angle between IOL optic and haptic was measured using the anterior IOL interface. These biometric data were determined in six different extracted B-scan sections taken from six stretching experiments (one IOL implanted in three different bags) followed by mean value determination.

The in vivo measurements were performed following the tenets of the Helsinki agreement. Written informed consent was obtained from all patients after the nature and possible consequences of the study were explained. Three-dimensional ultrasound biomicroscope measurements were performed after pharmacologically induced accommodation (pilocarpine 2%) or disaccommodation (cyclopentolate 1%) on two consecutive days.

The ciliary body regions of four patients were scanned 30 minutes after pharmacological treatment. For the biometric measurements, individual scans were extracted from the scanned three-dimensional volumes because movement artifacts prevent an analysis of oblique reconstructions through the voxel blocks to perform the biometry. Changes in haptic angulation and the IOL shift were analyzed (mean value) using six extracted B-scans. Positive values for AACD represent a forward shift of the IOL. For angulation determination, the point of origin was placed at the fulcrum as described above.

RESULTS

The three-dimensional reconstruction and interactive selection of sections across the haptic of the IOLs studied in the artificial capsular bag are shown in Figures 1 and 2. For the ICU (see Fig 1), the optic (O) and haptic (H) are well differentiated. The spot (*) in the equatorial region of the capsular bag is caused by the haptic ridge of the IOL, whereas this point is not always present under different scanning directions. The point (#) acts as the fulcrum and is used as the center of rotation for angulation determination. The echo pattern of the posterior convex side of the haptic is a falsified image due to time-delay effects. The fulcrum of the AT-45 is also marked (#), of which the three-dimensional reconstruction and image analysis is shown in Figure 2. Optic (O) and haptic (H) are well differentiated, whereas the echo pattern (*) is caused by the polyimide construction of the AT-45 plate haptic. The posterior lens surface could not be imaged.

B-scan series exemplifying the stretching experiments are depicted in Figure 4. The results concerning change in angulation optic haptic and axial shift are summarized in Figure 5. The B-scans of the ICU IOL show the effect of equatorial stretching/relaxing (max change in r = 0.5 mm). This maximal radius change induces an angulation change of 10.4° and an axial shift around 0.36 mm of the ICU. For the AT-45, a 9.3° angulation change and a 0.50-mm axial shift were found.

A basic knowledge of echo characteristics was used to describe the in vivo situation in patients with accommodative implants. Figure 6 shows a three-dimensional reconstruction and the image analysis (with design drawing) of the ICU haptic region. A haptic angulation of 6° compared with the relaxed IOL haptic is observed in this case.

Figure 4. A-C) B-scan series exemplifying the stretching experiment. B-scan of the ICU IOL showing the effect of equatorial stretching (max change in r = 0.5 mm). This stretching indicates a 10.4° angulation change and a 3.6-mm axial shift. Abbreviations: O = optic, PC = posterior capsule, H = haptic, AC = anterior capsule.Figure 5. Change in angulation (left) and axial IOL movement (right) by lens type showing the effect of equatorial stretching respectively relaxing (mean value±standard deviation). A change in r of 0.5 mm is a decrease/increase of the equatorial radius of the artificial capsular bag, comparable with a 0.5-mm shift of the ciliary body in lens direction during accommodation.

Figure 4. A-C) B-scan series exemplifying the stretching experiment. B-scan of the ICU IOL showing the effect of equatorial stretching (max change in r = 0.5 mm). This stretching indicates a 10.4° angulation change and a 3.6-mm axial shift. Abbreviations: O = optic, PC = posterior capsule, H = haptic, AC = anterior capsule.

Figure 5. Change in angulation (left) and axial IOL movement (right) by lens type showing the effect of equatorial stretching respectively relaxing (mean value±standard deviation). A change in r of 0.5 mm is a decrease/increase of the equatorial radius of the artificial capsular bag, comparable with a 0.5-mm shift of the ciliary body in lens direction during accommodation.

A detailed analysis of accommodative changes in axial lens shift (AACD) and haptic angulation was performed for four patients with the implanted ICU IOL. In Figure 7, the change in angulation shows the effect of cyclopentolate and pilocarpine in a 67-yearold patient 4 months postoperatively. For this patient, in comparison to the relaxed haptic configuration, a 4° angulation was observed using cyclopentolate. Pilocarpine induced an additional 10° angulation.

The results of the four eyes examined are summarized in Figure 8. In disaccommodation, a haptic angulation between 2° and 4° is visible. Pilocarpine induced an additional angulation change <10° for the ICU. In one case (patient 3), a haptic distortion was found. The haptic was positioned in an angle that results in a position anteriorly to the IOL optic plane and pilocarpine-induced ciliary muscle contraction caused a posterior IOL shift.

DISCUSSION

The biometrie analysis of high-frequency sonographic images becomes difficult if the information from only one A-scan section is possible. Regarding the analysis of haptic configurations, undefined tilting effects can falsify biometric measurements. The threedimensional ultrasound biomicroscopy combined with a powerful volume rendering software provides features such as volume orientation for viewing planes and three-dimensional perspectives. These features include an auxiliary tool for identification and biometrie analyzing of the haptic configuration with minimized tilting effects.

The posterior chamber lens ICU, which was developed based on FEM simulations by Küchle et al,11 was examined. Theoretically, a contraction of the ciliary muscle, thus a relaxation of the zonules, leads to a relaxation of the capsular bag. The haptics turn and produce an anterior axial shift according to the modified force ratio in the haptic region. Our simulation experiments show a similar effect during capsular bag relaxation. A 0.5-mm change in r was used for maximal relaxation/stretching, which is larger than the in vivo determined shifts of the ciliary muscle center of gravity using three-dimensional ultrasound biomicroscopy27 (max 0.26 mm) and magnetic resonance imaging28 (change in r [mm] = 0.5129-0.00525 × age [y]). With this unphysiological and unexpected amount of relaxation in humans, a 0.36-mm anterior shift was observed for the ICU caused by a haptic 10.4° angulation change. Using a 50-year lens and the linear regression of Strenk for the ciliary body displacement, a 0.25-mm ciliary body displacement can be assumed. A 0.28-mm anterior IOL shift and an angulation change of 4.3° was observed. For this lens, the theoretically predicted 30° haptic angulation change for 1-mm axial shift could not be achieved. Using Gullstrand's eye model and a 20-diopter (D) IOL placed in the capsular bag, a 1-mm anterior IOL shift causes a change in refraction of approximately 1.90 D in the spectacle plane.29 A 1-mm shift of a lens in the anterior chamber results in approximately a 1.20 D refraction change. Because the ICU is placed between the capsular bag and iris plane, a 0.28-mm anterior shift for the ICU produced a refraction change <0.53 D.

Figure 6. A, B) Three-dimensional reconstruction and C, D) image analysis (with design drawing) of the ICU haptic region in a 75-year-old patient 4 months postoperatively (disaccommodation). A 6° haptic angulation compared with the relaxed IOL condition is observed.

Figure 6. A, B) Three-dimensional reconstruction and C, D) image analysis (with design drawing) of the ICU haptic region in a 75-year-old patient 4 months postoperatively (disaccommodation). A 6° haptic angulation compared with the relaxed IOL condition is observed.

In the in vitro model, a maximal forward shift of 0.50 mm (9.3° haptic angulation change) for the AT-45 lens was observed using the maximal radius change of 0.5 mm. For 0.25-mm radius change as the expected value for the 50-year lens, an axial shift of 0.33 mm with 4.5° angulation change was found. Using Gullstrand's eye model, this shift of 0.33 mm causes a change in refraction <0.63 D. However, the measured shift does not correspond to the theoretical predictions for this lens. The AT-45 IOL was developed to transmit ciliary muscle activity into axial movement of the lens caused by ciliary muscle-induced variations in haptic angulation and vitreous pressure. In our model, equatorial changes can be simulated, but vitreous pressure variations cannot be simulated. Our observed anterior shift of the AT-45 optic therefore can only be caused by the modified geometric ratio in the haptic region, ie, the in vivo potential of this lens could be larger.

Regarding the axial shift, the AT-45 performed 0.14 mm better compared to the ICU for 0.5-mm radial displacement. This is remarkable, as the changes in angulation for both lenses are similar. From a geometrical viewpoint, this complex effect is hard to explain and cannot be elucidated completely. A reason could be the different design of the haptic contact point to the capsular bag or a deformation of the IOL optic.

Figure 7. Change in angulation of the ICU showing the effect of A) cyclopentolate and B) pilocarpine in a 67-year-old patient 4 months postoperatively. In comparison to the relaxed haptic configuration (180°), a 4° angulation (184°) could be observed using cyclopentolate. Pilocarpine induced an additional 10° angulation (194°). Abbreviations: S = sclera, I = iris, CB = ciliary body, H = haptic, 0 = optic.

Figure 7. Change in angulation of the ICU showing the effect of A) cyclopentolate and B) pilocarpine in a 67-year-old patient 4 months postoperatively. In comparison to the relaxed haptic configuration (180°), a 4° angulation (184°) could be observed using cyclopentolate. Pilocarpine induced an additional 10° angulation (194°). Abbreviations: S = sclera, I = iris, CB = ciliary body, H = haptic, 0 = optic.

Ultrasonographic patterns of the IOL haptics are used to explain the in vivo situation in patients with the ICU implant. Changes in angulation and AACD by four different individuals show the effect of cyclopentolate and pilocarpine 4 months postoperatively (see Fig 8). In disaccommodation, a haptic angulation between 2° and 4° caused by capsular bag shrinkage and secondary cataract formation is visible. This could mean that a haptic angulation is already present in the disaccommodated state. Also the effect seen in patient 3 is caused by the capsular bag shrinkage (see Fig 8). The IOL haptic is placed anteriorly to the IOL optic plane. In this case, pilocarpine treatment induced a posterior IOL shift (ΔACD = -0.4 mm).

In the cases studied, pilocarpine induced an additional angulation variation between 5° and 10° for the ICU IOL, which causes a change in anterior chamber depth between 0.2 and 0.5 mm. Using Gullstrand's eye model, this 0.2 -mm forward movement results in a refraction change <0.38 D (0.95 D for 0.5 mm of movement), depending on exact IOL position. These found ΔACD values are smaller than the findings of Langenbucher et al.30 A mean ACD decrease of 0.78 mm (0.49 to 1.26 mm) using the IOL-Master and 0.63 mm (0.34 to 1.12 mm) was found using ultrasound biometry after pilocarpine (6 months postoperatively). Our findings are in agreement with the results of Findl et al.17,18 Using partial coherence interferometry, Findl et al found a moderate forward movement under pilocarpine with an induced mean accommodative amplitude of 0.50 D. In conclusion, pilocarpine-induced ciliary muscle contraction caused a change in haptic angulation and an anterior shift of the ICU IOL, which resulted in approximately an estimated accommodative amplitude between 0.40 and 0.95 D.

Figure 8. Angulation and anterior chamber depth (ΔACD) by subject (implant ICU) showing the effect of cyclopentolate and pilocarpine (× = angle of difference to the relaxed haptic configuration, o = change under pilocarpine treatment; mean ± standard deviation). Positive values for ΔACD represent a forward shift of the IOL under pilocarpine.

Figure 8. Angulation and anterior chamber depth (ΔACD) by subject (implant ICU) showing the effect of cyclopentolate and pilocarpine (× = angle of difference to the relaxed haptic configuration, o = change under pilocarpine treatment; mean ± standard deviation). Positive values for ΔACD represent a forward shift of the IOL under pilocarpine.

Pilocarpine application is an objective way of stimulating accommodation as it requires no participation from the patient. Topical application of pilocarpine is advised and commonly used to stimulate accommodation.16-19,31-33 Variability in accommodation amplitudes is partially due to the capability and attendance of volunteers to accommodate to various kinds of stimuli. Using pilocarpine, this subjective component to accommodation is eliminated; however, the role of pilocarpine must be discussed.

Abramson et al32 measured the accommodation effect in human individuals using A-scan ultrasound. They determined a greater increase in axial lens diameter after pilocarpine application than is possible with stimulus -driven accommodation. Thus, topical application of pilocarpine may produce overstimulation of the ciliary muscle. These early results are consistent with the findings of Find34 and Köppl et al35 who used dual-beam partial coherence interferometry. These studies have shown a difference in lens movement between pilocarpine-induced and stimulus -driven ciliary muscle contraction. Pilocarpine acts "physiologically" in young phakics and as a superstimulus in presbyopic phakics and pseudophakes. Therefore, IOL movement and angulation change data may be overestimated when using pilocarpine.

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TABLE 1

Intraocular Lens Properties

Figure 1. Photograph and three-dimensional ultrasound biomicroscopy image and B-scan of the ICU in the artificial silicone capsular bag (CB). The optic (0) and haptic (H) are well differentiated. The spot (*) in the equatorial region of the capsular bag is caused by the haptic ridge of the I0L, whereas this point is not always present under different scanning directions. The point (#) acts as the fulcrum and is used as the center of rotation for angulation determination. The echo pattern of the posterior convex side of the haptic is a falsified image due to time-delay effects. Abbreviations: O = optic, # = fulcrum, H = haptic, and * = haptic ridge.

TABLE 2

Properties of the In Vitro Capsular Bag Model

10.3928/1081-597X-20050101-09

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