The final position of intraocular lenses (IOL) is a critical factor for refractive outcomes after cataract surgery.1,2 Many IOL designs rely on the capsular bag for positioning and can shift position as the bag changes during healing after cataract surgery.3,4
Femtosecond lasers for assisting cataract surgery are available and have shown some advantages both intraoperatively and postoperatively.5–12 Two advantages of laser-assisted cataract surgery are the reduction of ultrasound phacoemulsification energy after lens softening and precise laser capsulotomies.5–12 Some studies with laser-assisted cataract surgery have examined visual and refractive outcomes and IOL positioning compared to standard phacoemulsification.11,13–15 The underlying reasoning for these differences after the creation of the laser capsulotomy was not investigated.
Increased capsule strength in preclinical studies with laser capsulotomies indicates that there are differences between torn capsules in continuous curvlinear capsulorhexis (CCC) technique and laser capsulotomies.8,16 Additionally, the size of capsule aperture has been shown to contract less with laser capsulotomy than with a manual CCC.8
The introduction of the CCC in 1990 provided many surgical advantages, but introduced more frequent anterior capsule contraction than previous techniques such as the can-opener.17,18 Capsular bag shrinkage and anterior capsule contraction are common after modern cataract surgery with CCC and phacoemulsification, even in eyes with no comorbidities. Anterior capsule contraction has been associated with differences in centrifugal zonular forces and centripetal forces induced by capsular fibrosis.19,20 It seems possible that a precise complete capsulotomy, less zonular stress during the surgery, and the near elimination of ultrasound energy with laser-assisted cataract surgery lead to different capsule bag dynamics during healing. This is the first intraindividual study to examine the dynamics of capsular bag changes over 3 months of healing after standard cataract surgery and laser-assisted cataract surgery.
Patients and Methods
The trial received approval of the ethical committee of the Ruhr University in Bochum, Germany, and conformed to the tenets of the Declaration of Helsinki. All patients enrolled had a visually significant cataract (corrected distance visual acuity < 20/25) in both eyes, dilated pupil width of 6.0 mm or greater, and were willing to volunteer for the trial after giving an informed consent. The exclusion criteria included corneal scars, corneal diseases, corneal astigmatism of 1.5 diopters or greater, reduced endothelial cells, glaucoma, pseudoexfoliation syndrome, zonular weakness, single eye, malformations, history of ocular surgery, intraocular tumors, active or past inflammations, age-related macular degeneration, diabetic retinopathy, axial length difference (greater than 0.5 mm and less than 21.5 mm or greater than 26 mm), pregnancy, reduced compliance, age younger than 22 years, or participation in another clinical study.
All patients included underwent the same preoperative standardized management prior to the operation. For randomization, the patient was placed on the operating bed of the laser system and a corresponding envelope with the information about the receiving procedure was opened by the surgeon. All cases were HD-videotaped.
The two-step, 2.75-mm, primary clear cornea incision was created with a keratome at the 12-o’clock position. Two 1.2-mm paracenteses were placed at the 9- and 3-o’clock positions. After installation of ophthalmic viscoelastic devices (OVDs) (Healon 1%; Abbott Medical Optics, Santa Ana, CA) into the anterior chamber, the CCC was performed using a self-bent 19-gauge needle through the paracentesis. The intended diameter was 5.0 mm.
Laser-Assisted Cataract Surgery Group
A standardized treatment plan was used in all cases with a capsulotomy diameter of 5.0 mm and a lens softening pattern with a 350-μm grid size. The femtosecond laser-assisted treatment technique (Catalys Percision Laser System; Abbott Medical Optics) has recently been published.7,21,22 After docking, three-dimensional spectral-domain optical coherence tomography imaging of the anterior segment was performed, followed by automatic identification of the ocular surfaces. After verification of the treatment plan and any necessary adjustments, the surgeon started the laser treatment with the capsulotomy, followed by the lens fragmentation and softening as previously described.7 After undocking from the laser, prior to lens removal, all sideport and main incisions were created identical to standard phacoemulsification so no additional differences in technique were introduced.
All patients underwent small-incision phacoemulsification using topical anesthesia. Cataract surgery was performed using the Stellaris phacoemulsifcation machine (Bausch & Lomb, Rochester, NY) in both treatment groups with the thin tip needle. Identical phacoemulsification parameters and OVD were used in both groups. First the supranuclear cortex was removed by aspiration using the phacoemulsification tip. In the standard group, the nucleus was cracked with a Neuhann Chopper (Geuder, Heidelberg, Germany) and aspirated under further chopping and continuous phacoemulsification. In the laser group, a Neuhann chopper was inserted through one paracentesis and the softened nucleus was aspirated with minimal or without ultrasound phacoemulsification energy. Effective phacoemulsification time was recorded for all cases. Residual cortex removal and posterior capsule polishing was performed using bi-manual irrigation/aspiration through the nasal and temporal incisions.
After re-inflating the anterior chamber and capsular bag with OVD, a Koch capsule measuring ring (HumanOptics AG, Erlangen, Germany) was implanted. The capsular ring is a 12.0-mm diameter polymethylmethacrylate ring with 0.2-mm thick appendixes instead of eyelets, like a traditional capsular tension ring, on both ends. One appendix has a horizontal length of 1.0 mm, which represents a reference distance.23
Then a three-piece IOL (Tecnis ZA9003; Abbott Medical Optics) was implanted into the capsular bag. The Engel measuring device (Geuder AG) was used to ensure an anterior capsulotomy diameter of 5.0 ± 0.5 mm. After careful removal of the OVD, the corneal incisions were closed by hydration. Topical ofloxacin eye drops were administered three times daily for 5 days. Dexamethasone eye drops were administered four times daily for the first week, and then the dosage was gradually decreased over a period of 6 weeks.
IOL power calculations were performed using non-contact partial coherence laser interferometry (IOL-Master; Carl Zeiss Meditec, Jena, Germany). The Lens Opacities Classification System III (LOCS III) nuclear opalescence grading score reference was used.24 Preoperative nuclear opalescence was estimated by one independent physician using a BQ 900 Slit lamp (Haag-Streit, Bern, Switzerland) at maximum illumination without any light filtering. All laser-assisted cataract surgery and standard phacoemulsification procedures were followed by IOL implantation and performed by the same experienced surgeon (HBD).
Capsular Bag Measurements
The primary clinical endpoints of the study were the absolute capsular bag diameters and intraindividual difference in capsular bag diameters in millimeters.
Capsular bag measurements were taken on the day of surgery (postoperatively) and then at 3 and 7 days and 1, 2, and 3 months postoperatively (Figure 1). Measurements were taken directly at the slit lamp (BQ 900 Slit lamp). All slit-lamp measurements were done by a single trained technician who was blinded to the surgical technique. In the capsule measuring ring’s relaxed state, it has a diameter of 12.0 mm. The 1.0-mm transverse extension is used as an intraocular reference distance.25
(A) Capsular measuring ring (12 mm) in its relaxed state (1) and compressed capsular measuring ring (2) with overlapping appendices. (B) Slit-lamp photograph showing measurement ring after laser-assisted cataract surgery.
Prior to measurements, topical 0.5% tropicamide eye drops (Mydriaticum; Stulln Pharma, Stulln, Germany) and 5.0% phenylephrine eye drops (Neo-Synephrine; Ursapharm, Saarbrücken, Germany) were instilled two times within 30 minutes to induce mydriasis. The slit was adjusted to the appendix/distance of the measuring ring and the distance was recorded. The diameter in millimeters is calculated using a conversion table. The difference in amount of capsular bag shrinkage was calculated as an intraindividual measurement of the laser-assisted cataract surgery capsular bag diameter minus the standard capsular bag diameter.23
All descriptive statistical analysis was conducted using SPSS Version 19.0 (SPSS, Inc., Chicago, IL). The Friedman and post-hoc Wilcoxon signed rank tests were conducted to examine differences in the groups. To prevent an increase of the alpha error, a Bonferroni correction was applied. A P value of less than .01 was considered statistically significant. To compare between groups, the Mann–Whitney U test was performed. A Bonferroni correction was also applied and a P value of less than .0083 was considered statistically significant. Continuous variables were described with mean, standard deviation, median, and minimum and maximum values. Boxplots were used for the graphical illustration.
This prospective study involved 106 eyes of 53 patients (32 female, 21 male) with a follow-up of 3 months after cataract surgery. All patients were included in the 3-month follow-up. The average age of the study participants was 70.8 ± 7.9 years (range: 54 to 86 years).
The study was designed with comparable pairs of eyes (Table A, available in the online version of this article). The two groups did not differ statistically preoperatively in axial length or LOCS III grade. In none of the cases was the deviation from the targeted anterior capsulotomy diameter greater than 0.5 mm. The difference in capsular bag diameter immediately postoperatively was not statistically significant (P = .85). The laser group required less ultrasound energy to remove the softened nucleus than the standard group (laser group: 0.03 ± 0.01 sec, range: 0.00 to 0.48 sec; standard group: 1.25 ± 1.1 sec, range: 0.07 to 5.31 sec; P < .005). Furthermore, no ultrasound energy was used in 67% of the laser group.
The capsular bag diameters for the two groups are shown in Table 1 and Figure A (available in the online version of this article). The intraindividual differences in capsular bag diameter are demostrated in Figure 2. Between the second and third month, there was minimal but still statistically significant shrinkage according to the mean of the laser group (P < .001). However, there was no difference in the median capsular bag diameter of the laser group between 2 and 3 months postoperatively. Both the mean and median capsular bag diameter of the standard group were different between 2 and 3 months postoperatively. The mean percent shrinkage is demonstrated in Table B (available in the online version of this article). It was 5.0% in the laser group compared to 7.0% in the standard group during the first month, decreasing to 0.7% in the laser group compared to 1.0% between months 2 and 3. The total capsular bag shrinkage over the 3-month period was less with laser-assisted cataract surgery (6.9%) than standard phacoemulsification (10.3%).
Capsular Bag Diameter of Laser Cataract Surgery and Standard Groups
Boxplot of intraindividual difference in capsular bag diameter over time. The bottom and top of the box are the 25th and 75th percentiles, respectively, and the band near the center is the 50th percentile (median). The bars outside the box indicate the maximum and minimum of all data. A minor outlier (denoted by a small circle) is an observation 1.5× interquartile range outside the central box. The change is statistically significantly different (P < .001).
The difference in capsular bag shrinkage between eyes receiving laser-assisted cataract surgery eye and eyes receiving standard phacoemulsification was calculated for each of the 53 patients. A value of zero represents no difference between surgical modalities. Table B and Figure 2 show the intraindividual shrinkage at each of the measured six points in time. The laser group had statistically significantly less capsular bag shrinkage than the standard group at all time points from 1 to 3 months (P < .001).
Capsular bag shrinkage is important for IOL positioning and refractive outcomes after cataract surgery. It can lead to IOL decentration, tilt, and hyperopic shift.3,4 Shrinkage can start immediately after surgery but both the capsular bag and the area of the anterior capsular opening stabilize by 3 months postoperatively.23,26 Previous studies suggest that capsular bag shrinkage and stability of IOL positioning depend on anterior capsulorhexis size and shape, axial length, IOL material, and haptic design.27–29 This is the first intraindividual study to investigate the role of laser-assisted cataract surgery on capsular bag shrinkage.
The periphery of the capsular bag cannot be directly measured because it is not visible behind the iris. To accurately measure capsular bag diameters, a capsule measuring ring was used. This high resilience ring with a small spring constant has only minimal influence on the capsular bag shrinkage and does not negatively impact the patient or potential visual outcomes.26,30
Our study found a tendency toward earlier capsular bag diameter stabilization with laser-assisted cataract surgery than standard cataract surgery. Additionally, the absolute differences were significant starting at 1 month. The total capsular bag shrinkage over the 3-month postoperative period was less with laser-assisted cataract surgery compared to standard cataract surgery. Although comparable to published results, both groups were less than the 14% reported by Tehrani et al. with the same surgeon using the same capsular measuring ring.23 Possible explanations for this difference include different IOLs, different phacoemulsification machines and settings in 2003, and different surgical technique.
Capsular bag shrinkage can be inhibited with a capsule bending ring and to a lesser extent with a capsular tension ring. One advantage of capsular tension rings is the support of IOL positioning postoperatively and the reduced capsular bag shrinkage. They can be particularly useful in cases of comorbidities and premium IOLs such as toric and multifocal lenses that are more sensitive to positioning.30 Given the results presented here, it seems to be possible that, similar to capsular tension rings, laser-assisted cataract surgery induces less capsular bag shrinkage. Although laser-assisted cataract surgery appears to be a promising alternative, a future study could directly compare the reduction in capsular bag shrinkage with laser-assisted cataract surgery versus ultrasound phacoemulsification with capsular tension ring implantation.
Fibrosis is a response to injury and inflammation, typically seen in the capsule with injury to anterior lens epithelial cells causing metaplasia with myofibroblastic transformation. The fibrous connective tissue increases both anterior capsule contraction and capsular bag shrinkage.31–33 Studies indicate that the achieved size and the histological structure of laser-assisted cataract surgery capsultomies are different from those of standard CCC.8,34 An increased cell death with a demarcation line along the cutting edge was also found after femtosecond laser treatment.35 Furthermore, the pre-fragmented lens can be aspirated more easily with possibly less zonular stress.12,9 Our results show that there is less capsular bag shrinkage at all time points from 1 to 3 months. This suggests a different response to injury with laser-assisted cataract surgery.
Earlier capsular bag stability with laser-assisted cataract surgery indicates a potential for better, more predictable effective lens position, IOL power calculations, and refractive outcomes. Furthermore, our studies offer the first information for a priori power analysis for controlled studies comparing effective lens positioning standard to laser-assisted cataract surgery. With a proper study design, a sufficient statistical correlation between the capsular bag healing with laser-assisted cataract surgery, refraction, and visual acuity can be made.
- Holladay JT, Prager TC, Chandler TY, Musgrove KH, Lewis JW, Ruiz RS. A three-part system for refining intraocular lens power calculations. J Cataract Refract Surg. 1988;14:17–24. doi:10.1016/S0886-3350(88)80059-2 [CrossRef]
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- Behrouz MJ, Kheirkhah A, Hashemian H, Nazari R. Anterior segment parameters: comparison of 1-piece and 3-piece acrylic foldable intraocular lenses. J Cataract Refract Surg. 2010;36:1650–1655. doi:10.1016/j.jcrs.2010.05.013 [CrossRef]
- Sanders DR, Higginbotham RW, Opatowsky IE, Confino J. Hyperopic shift in refraction associated with implantation of the single-piece Collamer intraocular lens. J Cataract Refract Surg. 2006;32:2110–2112. doi:10.1016/j.jcrs.2006.07.030 [CrossRef]
- Nagy Z, Takacs A, Filkorn T, Sarayba M. Initial clinical evaluation of an intraocular femtosecond laser in cataract surgery. J Refract Surg. 2009;25:1053–1060. doi:10.3928/1081597X-20091117-04 [CrossRef]
- Conrad-Hengerer I, Hengerer FH, Schultz T, Dick HB. Effect of femtosecond laser fragmentation on effective phacoemulsification time in cataract surgery. J Refract Surg. 2012;28:879–883. doi:10.3928/1081597X-20121116-02 [CrossRef]
- Conrad-Hengerer I, Hengerer FH, Schultz T, Dick HB. Effect of femtosecond laser fragmentation of the nucleus with different softening grid sizes on effective phaco time in cataract surgery. J Cataract Refract Surg. 2012;38:1888–1894. doi:10.1016/j.jcrs.2012.07.023 [CrossRef]
- Friedman NJ, Palanker DV, Schuele G, et al. Femtosecond laser capsulotomy. J Cataract Refract Surg. 2011;37:1189–1198. doi:10.1016/j.jcrs.2011.04.022 [CrossRef]
- Abell RG, Kerr NM, Vote BJ. Toward zero effective phacoemulsification time using femtosecond laser pretreatment. Ophthalmology. 2013;120:942–948. doi:10.1016/j.ophtha.2012.11.045 [CrossRef]
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- Kránitz K, Takacs A, Miháltz K, Kovács I, Knorz MC, Nagy ZZ. Femtosecond laser capsulotomy and manual continuous curvilinear capsulorrhexis parameters and their effects on intraocular lens centration. J Refract Surg. 2011;27:558–563. doi:10.3928/1081597X-20110623-03 [CrossRef]
- Dick HB, Schultz T. On the way to zero phaco. J Cataract Refract Surg. 2013;39:1442–1444. doi:10.1016/j.jcrs.2013.07.002 [CrossRef]
- Lawless M, Bali SJ, Hodge C, Roberts TV, Chan C, Sutton G. Outcomes of femtosecond laser cataract surgery with a diffractive multifocal intraocular lens. J Refract Surg. 2012;28:859–864. doi:10.3928/1081597X-20121115-02 [CrossRef]
- Miháltz K, Knorz MC, Alió JL, et al. Internal aberrations and optical quality after femtosecond laser anterior capsulotomy in cataract surgery. J Refract Surg. 2011;27:711–716. doi:10.3928/1081597X-20110913-01 [CrossRef]
- Nagy ZZ, Kránitz K, Takacs AI, Miháltz K, Kovács I, Knorz MC. Comparison of intraocular lens decentration parameters after femtosecond and manual capsulotomies. J Refract Surg. 2011;27:564–569. doi:10.3928/1081597X-20110607-01 [CrossRef]
- Auffarth GU, Reddy KP, Ritter R, Holzer MP, Rabsilber TM. Comparison of the maximum applicable stretch force after femtosecond laser-assisted and manual anterior capsulotomy. J Cataract Refract Surg. 2013;39:105–109. doi:10.1016/j.jcrs.2012.08.065 [CrossRef]
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- Palanker DV, Blumenkranz MS, Andersen D, et al. Femtosecond laser-assisted cataract surgery with integrated optical coherence tomography. Sci Transl Med. 2010;2:58ra85. doi:10.1126/scitranslmed.3001305 [CrossRef]
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Figure A. Boxplot of capsule bag diameter over time for laser-assisted cataract surgery and standard phacoemulsification. The bottom and top of the box are the 25th and 75th percentiles, respectively, and the band near the center is the 50th percentile (median). The bars outside the box indicate the maximum and minimum of all data. A minor outlier (denoted by a small circle) is an observation 1.5× interquartile range outside the central box. The change is statistically significantly different over the whole postoperative period (P < .001).
Capsular Bag Diameter of Laser Cataract Surgery and Standard Groups
||Laser Cataract Surgery Mean ± SD (mm)
||Standard Mean ± SD (mm)
||Intraindividual Difference Mean ± SD (mm)
||10.47 ± 0.32
||10.46 ± 0.30
||0.01 ± 0.09
||10.29 ± 0.28
||10.19 ± 0.27
||0.10 ± 0.19
||10.14 ± 0.27
||10.01 ± 0.27
||0.13 ± 0.18
||9.95 ± 0.33
||9.75 ± 0.29
||0.20 ± 0.18
||9.83 ± 0.41
||9.53 ± 0.38
||0.30 ± 0.19
||9.76 ± 0.42
||9.43 ± 0.39
||0.33 ± 0.25