Preoperative and postoperative size and movements of the lens capsular bag: Ultrasound biomicroscopy analysis

ARTICLE

Preoperative and postoperative size and movements of the lens capsular bag: Ultrasound biomicroscopy analysis Marina Modesti, MD, Giacomo Pasqualitto, PhD, Rossella Appolloni, MD, Irene Pecorella, MD, Philippe Sourdille, MD

PURPOSE: To evaluate capsular bag size and accommodative movement before and after cataract surgery using ultrasound biomicroscopy (UBM) and anterior segment optical coherence tomography (AS-OCT). SETTING: Ophthalmology Unit, Fabia Mater Clinic, Rome, Italy. DESIGN: Cohort study. METHODS: Eyes having cataract surgery and monofocal intraocular lens (IOL) implantation were studied using UBM. The following parameters were measured preoperatively and 1, 2, and 12 months postoperatively: anterior chamber depth (ACD) (also by AS-OCT), capsular bag thickness, capsular bag diameter, ciliary ring diameter, sulcus-to-sulcus (STS) diameter, ciliary process–capsular bag distance, ciliary apex–capsular bag plane, and IOL tilting. The preoperative and postoperative capsular bag volumes were calculated at 12 months. The results were compared with the changes during accommodation. RESULTS: The study comprised 24 eyes. With the exception of the ciliary apex–capsular bag plane, which appeared to be unmodified postoperatively, all measured parameters showed significant variation after IOL implantation. Only the ACD did not change significantly during accommodation. CONCLUSIONS: After cataract surgery, the capsular bag stretched horizontally and with reduced vertical diameter as a result of adaptation to the implanted IOL. The capsular bag–IOL complex filled all available space, compressing the zonular fibers and almost abolishing the space between the ciliary apex and the capsular bag. There was anterior chamber deepening and a decrease in the ciliary ring diameter and STS diameter. In the absence of zonular fiber tension, the shape of the ciliary processes may be modified. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes. J Cataract Refract Surg 2011; 37:1775–1784 Q 2011 ASCRS and ESCRS

Restoring depth of focus and true accommodation after monofocal intraocular lens (IOL) insertion has triggered many studies during the past 10 years.1–3 The early work helped us understand and evaluate differences between pseudoaccommodation and real accommodation as well as the importance of the anatomic prerequisites for accommodation. Previous studies of a normal population showed large variability in lens and capsular bag diameter.4 Despite known individual differences in capsular bag diameter, such as found in postmortem eyes,4 little attention has been paid to the preoperative capsular bag diameter. Intraocular lens diameters vary from Q 2011 ASCRS and ESCRS Published by Elsevier Inc.

10.60 to 14.00 mm and are chosen using biometric measurement of the axial length (AL) of the eye without individual consideration of the actual capsular bag diameter. Complications of inappropriate IOL sizing include an overstretched capsular bag and IOL decentration and tilt.5 Cataract surgery with single-piece monofocal IOL implantation in the capsular bag allows partial anatomic and functional restoration of the bag and visual rehabilitation for distance. However, the lack of elasticity of the IOL optic prevents restoration of the true accommodative capacity in response to ciliary muscle contraction. Lately, there has been great 0886-3350/$ - see front matter doi:10.1016/j.jcrs.2011.04.035

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interest in the production of a pseudophakic IOL able to restore the accommodative capacity in patients having cataract surgery.1–3 Capsular bag elasticity and free IOL movement in the capsular bag are fundamental to maintaining pseudophakic accommodation. Some monofocal or accommodating IOLs were designed to follow the modifications of the capsular bag during the accommodative process by shifting the optics anteriorly in the active phase. The results have not been totally satisfactory. An additional obstacle to pseudoanatomic restoration of the capsular bag during cataract surgery is IOLs that are implanted without taking into account the real size of the capsular bag in he individual eye. The aim of this study was to evaluate the modifications in the anatomic structures of the anterior segment and capsular bag during accommodative physiologic stimuli in cataractous eyes before and after cataract surgery with IOL implantation. The changes were measured using high-frequency ultrasound biomicroscopy (UBM) and anterior segment optical coherence tomography (AS-OCT).

PATIENTS AND METHODS This study comprised eyes with advanced cortical and nuclear cataract that had standardized cataract surgery between January and March 2006. The study followed the tenets of the Declaration of Helsinki, and all patients provided informed consent. Exclusion criteria included a preoperative history of ocular trauma, other ophthalmic disease (eg, pseudoexfoliation syndrome, glaucoma, uveitis), and retinal disorders. The patients were examined preoperatively and 1, 2, and 12 months postoperatively. The examinations included clinical evaluation and UBM. Anterior segment OCT was also performed at 12 months.

Submitted: January 19, 2011. Final revision submitted: April 5, 2011. Accepted: April 21, 2011. From the Ophthalmology Unit (Modesti, Appolloni), Fabia Mater Clinic, the Research Center (Pasqualitto, Appolloni), Optikon 2000, and the Eye Clinic II Faculty (Appolloni) and Department of Experimental Medicine (Pecorella), University Sapienza, Rome, Italy; Clinique Sourdille (Sourdille), Nantes, France. Additional financial disclosures: Dr. Pasqualitto is the R&D manager for ultrasound diagnostic equipment, Optikon 2000, Rome, Italy. Presented in part at the XXV Congress of the European Society of Cataract & Refractive Surgeons, Stockholm, Sweden, September 2007. Corresponding author: Marina Modesti, MD, Ophthalmology Unit, Fabia Mater Clinic, via Olevano Romano 25-00100, Rome, Italy. E-mail: [email protected].

Surgical Technique The same surgeon (R.A.) performed all surgeries. The technique included superior self-sealing incisions, phacoemulsification, and IOL implantation in the capsular bag. In all cases, the IOL was an Acrysof SA60AT (Alcon Laboratories, Inc.) with an overall diameter of 13.0 mm and an optic diameter of 6.0 mm. The hydrophobic acrylic single-piece IOL was injected with a dedicated cartridge and injector.

Visual Acuity Corrected distance visual acuity (CDVA) was evaluated using Snellen fractions. Corrected near visual acuity (CNVA) was evaluated using Jaeger charts at 30 cm under subjective near-point accommodation with the minimum added positive sphere and using the push-up method (defocus test).

Anatomic Measurements The UBM was performed using a HiScan system (Optikon 2000) with a 35 MHz probe. This system has a tissue penetration depth to 8.0 mm. The entire anterior segment is represented in a single image with an axial resolution of 50 mm and lateral resolution of 70 mm. The scan is angular (8 scans/second); the image area is 15.0 mm  15.0 mm in normal-resolution mode and 5.0 mm  5.0 mm in high-resolution mode. The operator chooses the ultrasound velocity, which in this study was set at 1532 m/s for the anterior chamber and at 1550 m/s for all other parameters. The UBM examination was performed with the patient supine. After topical anesthesia (oxybuprocaine hydrochloride 0.4%) was administered, the eye was examined under constant photopic illumination conditions (190 lux) using a cup filled with a saline isotonic solution. To evaluate the anterior segment structures in relaxed accommodation, the patient was asked to focus with the eye not being examined on a cross-shaped target placed on the ceiling 3 m from the patient's head. The active accommodation condition was created by asking the patient to read a letter 30 cm from the eye not being examined and inducing physiologic accommodation using the subjective near point as the stimulus. Pharmacologic substances were not used because the goal was to evaluate accommodation in the physiologic state.6 The cataract or the IOL in the capsular bag was examined on the axial horizontal section (transverse diameter passing through the corneal apex from 3 to 9 o'clock) 2 times (for far vision and for near vision). Preoperatively, the cataract allowed easy discrimination of the capsular bag equator. After IOL implantation, the capsular bag equator was identified through the high reflectivity of the terminal portion of the haptics, the high reflectivity resulting from the collapsed anterior and posterior lens capsules, or both. The images thus obtained were stored as videos; images with the largest equatorial diameter were chosen using a slow-motion technique. The equatorial (sulcus-to-sulcus [STS]) diameter was measured on each frame, and the 2 images with the largest diameter were selected. During video acquisition, efforts were made to obtain the maximum perpendicularity and brightness of the areas of interest (cornea, anterior chamber, angle structures, pupil plane, STS maximum diameter, posterior chamber, crystalline lens, optic, IOL loops, capsular bag). Linear parameters on the selected images were determined using a zoom system, color analysis, 3-dimensional

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reconstruction,7–9 and an electronic calliper system. No correction factor was used for the measurements because the ultrasound diffractive error through tissue is irrelevant.10 In this study, only horizontal parameters were evaluated because a previous study11 did not detect significant variations in the mean differential values between the horizontal and vertical anterior segment parameters during relaxed accommodation and active accommodation. All measurements (Figure 1) were performed by the same trained examiner (M.M.).12 The anterior chamber depth (ACD) was measured in the center of the pupil, along the optical axis, from the corneal endothelium to the anterior surface of the crystalline lens preoperatively and from the corneal endothelium to the anterior surface of the IOL postoperatively. At the last follow-up examination, the ACD was also measured using AS-OCT (Visante, Carl Zeiss Meditec AG). The central capsular bag thickness was measured from the anterior to the posterior surface of the crystalline lens preoperatively and from the anterior surface of the IOL to the posterior surface of the lens capsule postoperatively. The maximum capsular bag diameter (equatorial poles from 3 to 9 o'clock in right eyes and from 9 to 3 o'clock in left eyes) was selected from the videos acquired preoperatively and postoperatively. The preoperative and postoperative ciliary ring diameter corresponded to the maximum distance between the ciliary apex processes from 3 to 9 o'clock in right eyes and from 9 to 3 o'clock in left eyes on the horizontal meridian. The STS diameter corresponded to the maximum distance between the ciliary sulcus recesses on the horizontal meridian from 3 to 9 o'clock in right eyes and from 9 to 3 o'clock in left eyes. The ciliary process–capsular bag distance corresponded to the zonular space between the capsular bag equator and the ciliary process apex. When the zonular space is compressed by the IOL, the capsular bag diameter and the ciliary ring diameter coincide. Negative measurements indicate over compression of the ciliary muscle. The ciliary apex–capsular bag plane was measured as the position of the capsular bag containing the crystalline lens or the IOL with respect to the plane passing through the ciliary process apexes. The capsular bag volume was calculated assuming that the shape of the lens preoperatively and postoperatively was oblate spheroid and by the equation a Z b O c, where

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a is the horizontal diameter, b is the vertical diameter, and c is the thickness. The formula is that used for an ellipsoid as follows: volume Z 4/3 p abc. The AS-OCT system used to measure the ACD at 12 months provides noncontact cross-sectional scans of the anterior segment with an axial resolution of 18 mm and a lateral resolution of 60 mm; the wavelength is 1310 nm. The image area is 16.0 mm  6.0 mm. The wavelength of the light source is absorbed by the pigmented epithelium of the iris; thus, imaging of structures posterior to the iris is not possible.13 Scans were obtained at the horizontal meridian (0 to 180 degrees). The images were displayed on a screen, and the ACD was measured using tools incorporated in the device. Intraocular lens tilt was measured as the distance between the IOL loops and the ciliary process apexes (mm) on the horizontal meridian. Tilt was present when only 1 loop was aligned with the ciliary process apex plane and the other loop appeared to be posterior to it.

Statistical Analysis The data were analyzed using SPSS software (version 13.0, SPSS, Inc.). Values recorded during relaxed accommodation (far vision) and those recorded during active accommodation (near vision) were compared. Pearson correlation coefficients were evaluated. A P value of 0.05 or less was considered statistically significant; a P value of 0.01 or less was considered highly statistically significant. The variation coefficient, which indicates the accuracy of measurements, was calculated at 12 months. The smaller the value, the higher the system's accuracy and adaptability for the specific parameters.

RESULTS The study enrolled 24 eyes of 19 patients (7 men, 12 women). The mean age at surgery was 69 years G 12 (SD) (range 46 to 87 years) and the mean AL, 22.96 G 1.19 mm (range 20.62 to 25.63 mm). The mean IOL power was C21.46 G 3.07 diopters (D) (range C17.0 to C30.0 D). No significant (affecting visual acuity) posterior capsule opacification occurred, and no eye required a neodymium:YAG capsulotomy. Refraction and Visual Acuity

Figure 1. Parameters measured using UBM (ACD Z anterior chamber depth; CA-CB plane Z ciliary apex–capsular bag plane; CBD Z capsular bag diameter; CBT Z capsular bag thickness; CPCBD Z ciliary process–capsular bag distance; CRD Z ciliary ring diameter; STS Z sulcus-to-sulcus diameter).

Table 1 shows the preoperative and postoperative refractive and visual acuity results. No relevant statistical correlations were found between the postoperative position of the IOL and the postoperative refraction. Ten eyes (41.67%) at 1 month and 2 months and 13 eyes (54.16%) at 12 months had high subjective postoperative accommodative capacity (using the added sphere for Jaeger [J] 2 near vision of 0.00 to 1.00 D). At 1 month, 10 eyes (41.67%) had medium subjective postoperative accommodative capacity (using the added sphere for J2 near vision of 1.00 to 2.00 D) and 4 eyes (16.66%) had low accommodative capacity (added sphere for J2 near vision of 2.00 to 3.00 D); there was no significant variation thereafter.

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Table 1. Preoperative and postoperative variation in the refractive parameters. Postoperative Parameter K1 (D) Mean G SD Range K2 (D) Mean G SD Range SE (D) Mean G SD Range CDVA Mean G SD Range CNVA (%) J2 J2 Near sphere added* (D) Mean G SD Range Near accommodative capacity† (D) Mean G SD Range

Preoperative

1 Month

2 Months

12 Months

44.30 G 1.75 40.00, 47.25

44.39 G 1.90 40.00, 47.00

44.40 G 1.85 39.50, 47.00

44.30 G 2.01 39.75, 48.00

44.54 G 1.62 40.75, 46.75

44.61 G 1.62 41.50, 47.00

44.67 G 1.54 41.50, 47.00

4.00 G 0.20 3.68, 4.36

0.03 G 0.39 1.00, 1.00

0.04 G 0.36 0.75, 1.00

0.09 G 0.26 0.75, 0.50

d d d d d

0.96 G 0.08 1.00, 0.70

0.99 G 0.04 1.00, 0.80

0.99 G 0.03 1.00, 0.90

d d

1.34 G 0.95 0.00, 3.00

1.40 G 1.08 0.00, 3.00

1.19 G 0.75 0.00, 3.00

d

6.02 G 4.82 0.50, 14.00

5.76 G 3.82 0.75, 15.60

4.60 G 1.69 2.33, 8.50

84 16

96 4

96 4

CDVA Z corrected distance visual acuity; CNVA Z corrected near visual acuity; J Z Jaeger; K1 Z keratometry in steep meridian; K2 Z keratometry in flat meridian; SE Z spherical equivalent *Minimum sphere added to obtain the best near acuity † Push-up technique

Anatomic Measurements Table 2 shows the mean preoperative and postoperative UBM anatomic measurements during relaxed accommodation and active accommodation. Cataract extraction caused an increase (45% at 1 month; 44% at 12 months) in the ACD, which remained stable postoperatively during relaxed accommodation and active accommodation. For example, UBM at 12 months showed no change in ACD during accommodation in 3 eyes (12.50%), a mean increase of 100 mm in 9 eyes (37.50%), and a mean decrease of 73 mm in 12 eyes (50.00%). Anterior segment OCT showed no change in ACD during accommodation in 3 eyes (12.50%), a mean increase of 71 mm in 8 eyes (33.33%), and a mean decrease of 92 mm in 13 eyes (54.17%). There was an 85% postoperative reduction in capsular bag volume from a mean of 198 G 28 mm3 preoperatively to a mean of 29 G 5 mm3 postoperatively. The relaxed preoperative capsular bag thickness decreased significantly between preoperatively and 1 month postoperatively, with no significant changes thereafter. The preoperative ciliary apex–capsular bag plane position was central in 14 eyes (58.33%) and posterior

to the ciliary apex in 10 eyes (41.67%); no eye had a tilted capsular bag plane. At 1 month, the plane position was central in 10 eyes (41.67%) and posterior to the ciliary apex in 9 eyes (37.50%); slight tilt (1 IOL loop located in recess between ciliary processes) was recorded in the remaining 5 eyes (20.83%). Two additional eyes had tilting of the capsular bag–IOL complex at subsequent follow-ups. The mean preoperative relaxed plane position was not significantly modified after IOL implantation except with active accommodation, during which it increased slightly at 1 month. There was, therefore, a tendency for the posterior planes to move backward during active accommodation with slight, not statistically significant, deepening of the anterior chamber. In the first postoperative month, the capsular bag during active accommodation moved backward in 11 eyes (45.83%) and forward in 3 eyes (12.50%); there was no movement in 10 eyes (41.67%). There was no further change thereafter. In no eye was the preoperative or postoperative ciliary apex–capsular bag plane anterior to the ciliary apex. In the 5 cases with IOL tilt at 1 month, the plane position ranged from 0.10 to 0.67 mm (mean 0.28 mm). Data analysis showed a statistically significant

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Table 2. Preoperative and postoperative variation in the anatomic parameters based on accommodation. Postoperative 12 Months Parameter/Accommodation ACD (mm) Relaxed Mean G SD Range VC (%) Active Mean G SD Range VC (%) Difference Mean G SD P value CBD (mm) Relaxed Mean G SD Range VC (%) Active Mean G SD Range VC (%) Difference Mean G SD P value CBT (mm) Relaxed Mean G SD Range VC (%) Active Mean G SD Range VC (%) Difference Mean G SD P value CBV (mm3) Relaxed Mean G SD Range Active Mean G SD Range Difference Mean G SD P value CRD (mm) Relaxed Mean G SD Range VC (%)

Preoperative

1 Month

2 Months

UBM

AS-OCT

2.79 G 0.45 1.48, 3.50 d

4.04 G 0.19 3.69, 4.38 d

3.98 G 0.21 3.63, 4.38 d

4.02 G 0.19 3.72, 4.35 0.71

4.01 G 0.18 3.68, 4.39 d

2.75 G 0.48 1.34, 3.48 d

4.07 G 0.19 3.71, 4.38 d

4.01 G 0.21 3.68, 4.37 d

4.00 G 0.20 3.68, 4.36 0.70

3.99 G 0.20 3.68 to 4.36 d

0.04 G 0.08 .01509

0.04 G 0.09 .03987

0.03 G 0.13 .15233

0.02 G 0.07 .08892

0.03 G 0.10 .09306

9.37 G 0.61 8.20, 10.44 d

9.76 G 0.65 8.53, 11.12 d

9.69 G 0.63 8.56, 11.08 d

9.68 G 0.65 8.50, 11.12 0.27

d d d

9.35 G 0.67 8.25, 10.70 d

9.63 G 0.66 8.44, 11.15 d

9.61 G 0.56 8.50, 10.81 d

9.59 G 0.58 8.48, 10.75 0.30

d d d

0.02 G 0.26 .36131

0.13 G 0.31 .02848

0.08 G 0.22 .04824

0.10 G 0.14 .00144

d d

4.31 G 0.61 3.30, 5.77 d

0.58 G 0.08 0.48, 0.71 d

0.57 G 0.06 0.48, 0.70 d

0.57 G 0.06 0.48, 0.67 2.06

d d d

4.35 G 0.63 3.29, 5.76 d

0.58 G 0.08 0.46, 0.73 d

0.58 G 0.07 0.48, 0.71 d

0.58 G 0.05 0.49, 0.68 2.50

d d d

0.04 G 0.07 .01471

0.00 G 0.03 O.05

0.01 G 0.02 !.01

0.01 G 0.03 O.05

d d

197.0 G 28.2 137.0, 244.0

29.2 G 5.5 21.6, 43.6

28 G 5.4 21.3, 41.5

28.2 G 5.0 20.4, 40.2

d d

198.0 G 31.0 137.0, 253.0

28.4 G 6.4 21.0, 43.8

28 G 5.1 21.6, 41.3

28 G 4.7 21.3, 40.4

d d

0.95 G 11.5 O.05

0.82 G 2.18 !.05

0.07 G 1.66 O.05

0.19 G 1.63 O.05

d d

9.66 G 0.56 8.58, 10.61

9.52 G 0.63 8.37, 11.09

9.52 G 0.62 8.20, 10.59

9.54 G 0.59 8.27, 10.50 0.42

d d d

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Table 2. (Cont.) Postoperative 12 Months Parameter/Accommodation Active Mean G SD Range VC (%) Difference Mean G SD P value SSD (mm) Relaxed Mean G SD Range VC (%) Active Mean G SD Range VC (%) Difference Mean G SD P value CP-CBD (mm) Relaxed Mean G SD Range VC (%) Active Mean G SD Range VC (%) Difference Mean G SD P value CP-CB plane (mm) Relaxed Mean G SD Range VC (%) Active Mean G SD Range VC (%) Difference Mean G SD P value

Preoperative

1 Month

2 Months

UBM

AS-OCT

9.63 G 0.55 8.64, 10.65 d

9.40 G 0.61 8.04, 11.10 d

9.38 G 0.61 8.13, 10.52 d

9.36 G 0.59 8.15, 10.46 0.37

d d d

0.03 G 0.23 O.05

0.11 G 0.20 .01

0.14 G 0.20 .01

0.18 G 0.18 !.0001

d d

10.25 G 0.49 9.20, 11.35 d

10.11 G 0.65 8.72, 11.22 d

10.10 G 0.62 8.68, 11.04 d

10.07 G 0.64 8.63, 11.01 0.33

d d d

10.11 G 0.51 9.23, 11.09 d

9.88 G 0.66 8.27, 11.24 d

9.90 G 0.66 8.50, 10.78 d

9.84 G 0.67 8.47, 10.69 0.34

d d d

0.14 G 0.26 !.001

0.23 G 0.24 !.0001

0.20 G 0.21 !.0001

0.23 G 0.20 !.0001

d d

0.29 G 0.44 0.00, 1.28 d

0.24 G 0.45 1.71, 0.44 d

0.17 G 0.42 1.57, 0.62 d

0.14 G 0.45 1.61, 0.68 57.0

d d d

0.27 G 0.52 0.00, 1.24 d

0.23 G 0.45 1.33, 0.34 d

0.23 G 0.43 1.63, 0.42 d

0.22 G 0.45 1.65, 0.63 133.0

d d d

0.01 G 0.36 O.05

0.02 G 0.39 O.05

0.06 G 0.28 O.05

0.08 G 0.21 !.0001

d d

0.15 G 0.19 0.0, 0.50 d

0.15 G 0.18 0.0, 0.67 d

0.16 G 0.17 0.0, 0.60 d

0.16 G 0.17 0.00, 0.50 8.1

d d d

0.14 G 0.19 0.00, 0.50 d

0.18 G 0.20 0.00, 0.73 d

0.19 G 0.20 0.00, 0.78 d

0.18 G 0.17 0.00, 0.48 7.8

d d d

0.01 G 0.02 .03843

0.03 G 0.07 .04845

0.03 G 0.05 .00268

0.02 G 0.04 .05474

d d

ACD Z anterior chamber depth; AS-OCT Z anterior segment optical coherence tomography; CBD Z capsular bag diameter; CBT Z capsular bag thickness; CBV Z capsular bag volume; CP–CB plane Z capsular bag–IOL position in respect to ciliary apex; CP–CBD Z ciliary process–capsular bag distance; CRD Z ciliary ring diameter; SSD Z sulcus-to-sulcus distance; UBM Z ultrasound biomicroscopy; VC Z variation coefficient

correlation between IOL tilt and the posterior ciliary apex–capsular bag plane (P!.001). There was a mean postoperative reduction in the ciliary ring diameter and STS of 0.14 mm. The ciliary

ring diameter (Figure 2) and STS diameter decreased further during postoperative accommodative stimuli, possibly as a consequence of restored ciliary muscle activity. These results were stable at all follow-up

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of ciliary muscle contraction and filling of the zonular area. At 1 month and thereafter, the ciliary process– capsular bag distance was close to nil in both phases, indicating enlargement of the capsular bag diameter and thus a partial obstacle to ciliary muscle activity (Figure 5). DISCUSSION

Figure 2. Ciliary ring diameter active accommodation over time.

examinations. This finding was associated with a larger postoperative capsular bag diameter on relaxed accommodation. The relaxed preoperative capsular bag diameter increased slightly, but not significantly, postoperatively (Figure 3). Although there was immediate enlargement in the capsular bag, the size decreased somewhat during the first 2 to 3 months as a result of capsular bag contraction. Some anterior capsule fibrosis was also noted by 3 months postoperatively. Although there was no accommodative variation in preoperative capsular bag diameter, there was a decrease at all postoperative follow-ups, indicating some degree of capsule elasticity (Figure 4). During active accommodation, the loops of the IOL showed anterior bowing in 17 eyes (70.83%) at 1, 2, and 12 months. Before IOL implantation, the ciliary process–capsular bag distance was greater during relaxed accommodation than during active accommodation as a result

The aim of this study was to measure the anatomic variations in the anterior segment induced by IOL implantation and by physiologic accommodation stimuli before and after cataract surgery, mainly using ultrasound scans. Thus, only eyes with advanced cataract were eligible for the ultrasound examination because they allowed better assessment of the equatorial diameter. Although it has been suggested that the results of laser interferometry are more reproducible than those obtained by UBM or OCT when assessing capsule dynamics after cataract surgery,5 the number of eyes we evaluated in the present study was large enough to minimize possible bias. A possible limitation of this study is the use of subjective methods, such as the push-up method and the dioptric correction, in the evaluation of the accommodative capacity, mainly because of the uncertainty about the accommodative strength used by the patient. Most patients indicate as defocused the characters they are unable to read. However, according to Anderson et al.,14 although subjective methods tend to slightly overevaluate the result, the trend does not differ from objective methods in which drugs are used. Intraocular lens implantation is generally considered to cause modifications in the shape of the capsular bag, including postoperative flattening, increased

Figure 3. Ultrasound biomicroscopy images. Left: Preoperative active accommodation capsular bag diameter (red line) (8.91 mm) and capsular bag thickness (green line) (3.30 mm). Right: Postoperative accommodation capsular bag diameter (green line) (9.17 mm) and STS diameter (red line) (9.63 mm). J CATARACT REFRACT SURG - VOL 37, OCTOBER 2011

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Figure 4. Capsular bag diameter over time.

Figure 5. Ciliary process–capsular bag distance graph over time.

diameter, and decreased diameter resulting from centripetal movement of the ciliary processes during accommodation. We noticed that in most cases, active accommodation was associated with anterior bowing of the IOL loops and with a decrease in capsular bag diameter. We also found that the enlargement of the capsular equatorial diameter (capsular bag diameter) was associated with a decreased distance from the ciliary apexes (ciliary process–capsular bag distance), seemingly as a result of compression of the zonules. As others have suggested,5 the enlargement may be caused by the use of oversized, not custom, IOLs. The limitation in the available zonular space could, in turn, reduce the amplitude of the contractile movements of the ciliary apparatus. Nevertheless, a residual contractile capacity of the ciliary muscle was apparent at all our postoperative follow-ups as the apexes of the processes moved centripetally after accommodative stimuli and further reduced the ciliary process–capsular bag distance, which then became a negative value. Unfortunately, these measurements were below the resolution range of the available UBM systems (0.050 mm/50 mm) and could not be accurately determined. The variation coefficient results in these cases (56% to 133%) showed that the measurements were at the limit of the system's resolution. Although the decrease in the zonular space may not be relevant with the use of monofocal IOLs because of their mechanical resilience in withstanding ciliary contraction forces, this finding should be kept in mind when designing new accommodating IOLs. The reduction in capsular bag diameter that we observed in pseudophakic eyes during accommodative stimuli, although of little amplitude, points to the capsular bag's residual elasticity in the postoperative period. The capsular bag, therefore, does not seem to be totally rigid, despite the fibrotic thickening that usually develops in the first postoperative trimester.5,15 There were no cases of capsular

bag retraction in our series at the 1-year follow-up as confirmed by the stable capsular bag diameter measurements. The ciliary ring diameter and STS diameter were less than in the cataractous eyes and appeared to markedly decrease during active accommodation in the pseudophakic eyes. This confirms our previous findings11 and the results in other published studies of changes in the cilitary sulcus anatomy.16–18 Possibly, overall modification of the ocular inner geometry occurs after IOL implantation. Despite capsular bag diameter enlargement, a reduction in ciliary ring diameter was observed. This might indicate that opposite mechanical forces, caused by an anterior vitreal shift and posterior repositioning of the ciliary processes secondary to flattening of the capsular bag, induce centripetal stretching of the ciliary processes. Other studies19–20 did not find a further reduction in the ciliary ring diameter after IOL implantation. However, the measurements in these studies were performed using magnetic resonance imaging, which is a rather static method compared with UBM because UBM allows continuous monitoring of the movements of inner ocular structures. With uncomplicated surgery and in the absence of accommodative stimuli, the preoperative ciliary apex–capsular bag plane position did not vary in the pseudophakic eyes we examined. Our postoperative data essentially agree with those of Wirtitsch et al.,21 who found that under relaxed conditions, there was essentially no change in the position of single-piece IOLs in the first postoperative year, despite capsule shrinkage and fusion of the anterior and posterior leaves of the capsular bag. An additional confirmation of our findings of no variation in the ciliary apex–capsular bag plane postoperatively is the lack of significant ACD modification after accommodative stimuli at all postoperative examinations. The finding of a stable ACD could be the result of the limited resolution of the scan system; in fact, the variation at all follow-up

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visits was not statistically significant (PZ.08). However, another study using partial coherence interferometry reports similar results.21 The preoperative capsular plane position was posterior in 42% of eyes in our study, possibly because our study comprised cases with advanced cataract and UBM measurements were performed with the patient supine. In 7 eyes (29%) in which the preoperative capsular plane position was posterior, the capsular bag–IOL complex shifted farther back postoperatively and there was slight (not statistically significant) deepening of the anterior chamber during active accommodation. Another study that used subjective near point as the stimulus22 found forward IOL movement of 0.04 mm. In our study, the postoperative posterior ciliary apex–capsular bag plane was statistically correlated with IOL tilt (PZ.001). The more posterior the plane, the higher the possibility of bag–plane misalignment, with correct alignment of 1 IOL loop in the ciliary apex and insertion of the other loop in the more posterior interciliary sulcus. A possible explanation for this is that posterior planes are associated with altered zonular fibers that are unable to prevent capsule tilting when an oversized IOL is implanted. Results, however, do not indicate a correlation between IOL tilting and astigmatism, whereas the former was associated with a significant increase in accommodative capacity at 12 months (PZ.005); that is, the greater the tilt, the lower the added sphere and the better the accommodative capacity. Astigmatism was dependent on corneal shape, as shown by our keratometry measurements, and was not correlated with subjective (added sphere and push-up method) accommodative capacity. Nishi et al.23 obtained the same results in a study of the relationship between apparent accommodation and against-the-rule astigmatism. Capsular bag shrinkage combined with IOL design and material may be responsible for the changes in the postoperative IOL position.24 However, IOL tilt did not appear to be associated with postoperative capsular shrinkage in the present study because we found stable enlargement of the capsular bag diameter. The axial position of the tilted capsular bag–IOL complexes did not vary during accommodation, and the reduction in the capsular bag–ciliary apex distance was small. A decrease in the number of eyes with a postoperative central ciliary apex–capsular bag plane position (10 versus 14 preoperatively) and the increase in IOL tilt may be the result of the implantation of an IOL that was too large for the capsular bag. Thus, the diameter of the IOL must closely match that of the crystalline lens. In our study, 42% of eyes at 1 and 2 months and 54% at 12 months had good subjective accommodative capacity, which appeared to be independent of the

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central plane position. We did not find a statistical correlation between alignment of the ciliary apex and capsular bag and accommodative capacity. We also did not find a correlation between accommodative capacity, plane position, IOL tilt, and preoperative lens volume. However, there was a statistically significant correlation between the preoperative and postoperative capsular bag volume difference and the ciliary apex–capsular bag plane position (P!.001); the greater the difference in the preoperative and postoperative capsular bag volume, the greater the possibility of a posterior or tilted ciliary apex–capsular bag plane. We also did not find a significant correlation between accommodative capacity, the ciliary apex–capsular bag plane position, the ACD, and myopic astigmatism. Pseudoaccommodative phenomena could, at least in these instances, be the result of an increase in the depth of focus secondary to a small pupil. However, despite the general understanding that pseudophakic eyes cannot accommodate and that apparent accommodation relies on an increase in the depth of focus,25 the small changes we observed in the measurements confirm that the accommodative apparatus still functions. True pseudophakic accommodation, as that caused by ciliary muscle contraction, might be better with the use of IOLs of softer materials that do not enlarge the capsular bag and that are aligned with the ciliary apex plane. Our findings of a reduction in ciliary ring diameter and STS diameter during active accommodation and a postoperative posterior ciliary apex–capsular bag plane, together with a good subjective accommodative capacity, are interesting in view of the results obtained by Findl et al.5 in a study of IOL movement caused by ciliary muscle contraction. These authors stated that a deep ACD caused slightly more IOL movement in the plate–haptic group than a shallower ACD and suggested posterior positioning of the IOL to obtain anterior movement of the IOL. In their opinion, the finding was in agreement with the theory that IOL movement is not induced by radial contraction of the ciliary muscle on the haptics but rather by vitreous pressure from behind after muscle contraction. Our results, however, cannot confirm the hypothesis of vitreal posterior pressure. In conclusion, we believe that our results may prove helpful in improving IOL design to obtain optimum predictable performance in the capsular bag. To our knowledge, this is the first study to compare the preoperative and postoperative size and movements of the capsular bag with a 1-year follow-up in consecutive patients having cataract extraction. Postoperatively, the capsular bag is frequently enlarged and misaligned in the ciliary plane. An IOL in a poor anatomic position prevents optimum zonule action,

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which is the key to potential true accommodation. Better adaptation of the IOL to the changes in capsular bag diameter seems to be necessary to improve the precision and stability of the refraction and would be the first step to designing a truly accommodative IOL. Our findings of modified ocular inner geometry after IOL implantation, in particular ciliary ring diameter reduction, further stress the need for better IOL tailoring and for smaller IOLs. REFERENCES 1. Nishi J, Mireskandari K, Khaw P, Findl O. Lens refilling to restore accommodation. J Cataract Refract Surg 2009; 35:374–382 2. Findl O, Leydolt C. Meta-analysis of accommodating intraocular lenses. J Cataract Refract Surg 2007; 33:522–527 3. Werner L, Olson RJ, Mamalis N. New technology IOL optics. Ophthalmol Clin North Am 2006; 19(4):469–483 4. Dong E-Y, Joo C-K. Predictability for proper capsular tension ring size and intraocular lens size. Korean J Ophthalmol 2001; 15:22–26. Available at: http://pdf.medrang.co.kr/paper/pdf/Kjo/ Kjo015-01-04.pdf. Accessed May 22, 2011 5. Findl O, Kiss B, Petternel V, Menapace R, Georgopoulos M, Rainer G, Drexler W. Intraocular lens movement caused by ciliary muscle contraction. J Cataract Refract Surg 2003; 29:669–676 6. Koeppl C, Findl O, Kriechbaum K, Drexler W. Comparison of pilocarpine-induced and stimulus-driven accommodation in phakic eyes. Exp Eye Res 2005; 80:795–800 7. Brodlie KW, Carpenter LA, Earnshaw RA, Gallop JR, Hubbold RJ, Mumford AM, Osland CD, Quarendon P. Scientific Visualization: Techniques and Applications. Berlin, Germany, Springer-Verlag, 1992 8. Kaufman AE, Sobierajski LM. Continuum volume display. In: Gallagher RS, ed, Computer Visualization Graphics: Techniques for Scientific and Engineering Analysis. Boca Raton, FL, CRC Press, 1995; 171–202 9. Krestel E. Imaging Systems for Medical Diagnostics: Fundamentals and Technical Solutions - X-Ray Diagnostics - Computed Tomography - Nuclear Medical Diagnostics - Magnetic Resonance Imaging - Ultrasound Technology. Munich, Germany, Siemens-Aktiengesellschaft, 1990 10. Silverman RH. Ultrasound versus AC OCT [letter]. J Cataract Refract Surg 2005; 31:1475 11. Marchini G, Pedrotti E, Modesti M, Visentin S, Tosi R. Anterior segment changes during accommodation in eyes with a monofocal intraocular lens: high-frequency ultrasound study. J Cataract Refract Surg 2008; 34:949–956 12. Tello C, Liebmann J, Potash SD, Cohen H, Ritch R. Measurement of ultrasound biomicroscopy images: intraobserver and interobserver reliability. Invest Ophthalmol Vis Sci 1994; 35:3549–3552. Available at: http://www.iovs.org/cgi/reprint/35/ 9/3549. Accessed May 22, 2011 13. Baikoff G, Lutun E, Wei J, Ferraz C. Anterior chamber optical coherence tomography study of human natural accommodation in a 19-year-old albino. J Cataract Refract Surg 2004; 30:696–701

14. Anderson HA, Glasser A, Manny RE, Stuebing KK. Age-related changes in accommodative dynamics from preschool to adulthood. Invest Ophthalmol Vis Sci 2010; 51:614–622. Available at: http://www.iovs.org/content/51/1/614.full.pdf. Accessed May 22, 2011 15. Menapace R, Findl O, Kriechbaum K, Leydolt-Koeppl C. Accommodating intraocular lenses: a critical review of present and future concepts. Graefe Arch Clin Exp Ophthalmol 2007; 245: 473–489 16. Gimbel HV, Sanders DR, Raanan MG. Visual and refractive results of multifocal intraocular lenses. Ophthalmology 1991; 98:881–887; discussion by JT Holladay, 888 17. Cumming JS, Slade SG, Chayet A, and the AT-45 Study Group. Clinical evaluation of the model AT-45 silicone accommodating intraocular lens; results of feasibility and the initial phase of a Food and Drug Administration clinical trial. Ophthalmology 2001; 108:2005–2009; discussion by TP Werblin, 2010 18. Hara T, Hara T, Yasuda A, Yamada Y. Accommodative intraocular lens with spring action. Part I. Design and placement in an excised animal eye. Ophthalmic Surg 1990; 21:128–133 19. Strenk SA, Strenk LM, Guo S. Magnetic resonance imaging of the anteroposterior position and thickness of the aging, accommodating, phakic, and pseudophakic ciliary muscle. J Cataract Refract Surg 2010; 36:235–241 20. Strenk SA, Strenk LM, Guo S. Magnetic resonance imaging of aging, accommodating, phakic, and pseudophakic ciliary muscle diameters. J Cataract Refract Surg 2006; 32:1792–1798 21. Wirtitsch MG, Findl O, Menapace R, Kriechbaum K, Koeppl C, Buehl W, Drexler W. Effect of haptic design on change in axial lens position after cataract surgery. J Cataract Refract Surg 2004; 30:45–51 22. Wang H, Zhang Y, Guan J. [Apparent accommodation in pseudophakic eyes after implantation of posterior chamber intraocular lenses]. [Chinese] Zhonghua Yan Ke Za Zhi 1996; 32:291– 294 23. Nishi T, Nawa Y, Masuda N, Yoshii T, Uemura S, Kato Y, Hara Y. [Relation between apparent accommodation and against-the-rule astigmatism]. [Japanese] IOL & RS 2003; 17: 445–448 24. Koeppl C, Findl O, Kriechbaum K, Sacu S, Drexler W. Change in IOL position and capsular bag size with an angulated intraocular lens early after cataract surgery. J Cataract Refract Surg 2005; 31:348–353 25. Elder MJ, Murphy C, Sanderson GF. Apparent accommodation and depth of field in pseudophakia. J Cataract Refract Surg 1996; 22:615–619

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First author: Marina Modesti, MD Ophthalmology Unit, Fabia Mater Clinic, Rome, Italy