Accurate astigmatism management during cataract surgery, whether using toric IOLs or corneal incisions, benefits from accurate eye markings to identify a reference position (eg, the horizontal axis) and the axis of (steep) astigmatism. It has been estimated that a 5° alignment error of a toric IOL against the expected angle may result in an error of 17% in anticipated effect.1
Although the presumed horizontal axis of the eye can be determined by placing ink marks on the eye with the patient in an upright, seated position, the patient is placed in a supine position during surgery, which may result in a variable degree of cyclorotation. The astigmatism axis can be tracked using the marked axis as a reference.2,3 Placement error with ink markings may result in a combined axis mean error of 4.9°, resulting in theoretical residual astigmatism errors of 0.17 and 0.34 D for eyes with 1.00 and 2.00 D of corneal astigmatism, respectively.1 However, theoretical error may be unequal to measured error owing to the subjective component of the refractive outcome and the effects of the incision and other refractive surfaces of the eye (ie, posterior corneal surface and vitreous).
The VERION system (Alcon Laboratories, Inc., Fort Worth, TX) was introduced to provide automated tracking. This system has several components, including the measurement module, the vision planner, and the digital markers M (microscope) and L (laser). The image-guided planning system provides integrated digital guidance for alignment of the corneal incision and the toric IOL axis.
This study was performed to determine the proportion of eyes with preexisting astigmatism that achieved 0.50 D or less of residual refractive cylinder 3 months after implantation of toric IOLs or corneal incisions using the image-guided measurement module and digital markers M and L.
Patients and Methods
This was an open-label, prospective, observational, non-randomized, multicenter four-arm study, with data collected from four centers in the United States and one center in France. All eyes underwent cataract removal by phacoemulsification using a femtosecond laser image-guided system for standard surgical planning. Patients subsequently had implantation of toric or non-toric monofocal or multifocal IOLs. Surgery was performed by one surgeon at each site, with each surgeon using his or her own A-constant and preferred surgical technique, including preferred incision size and capsulotomy diameter.
Table 1 shows the procedures used in the four study arms. Eyes in the no laser treatment group underwent implantation of AcrySof IQ ReSTOR multifocal toric IOLs (Alcon Laboratories, Inc.) with the measurement module, vision planner, and digital marker M. Eyes in the toric, monofocal, and multifocal groups underwent implantation of AcrySof IQ toric, AcrySof IQ monofocal, and AcrySof IQ ReSTOR multifocal IOLs, respectively, each using the measurement module, vision planner, digital marker M, and digital marker L with the use of the LenSx laser (Alcon Laboratories, Inc.). The monofocal and multifocal groups both used astigmatic keratotomy with paired arcuate incisions. All eyes were evaluated preoperatively (baseline) and 3 months postoperatively.
Description of Study Groups (Intention-to-Treat Set)
Patients who were determined by the investigator to be eligible for implantation of multifocal toric IOLs but who opted for the procedure without LenSx laser treatment were sequentially assigned to the no laser treatment group. Patients who were determined by the investigator to be eligible for implantation of toric IOLs and who elected to undergo LenSx procedures were assigned to the toric group. Patients who were determined by the investigator to be eligible for implantation of monofocal and multifocal IOLs and who elected to undergo LenSx procedures were sequentially assigned to the monofocal and multifocal groups, respectively.
Patients 18 years and older who were eligible to undergo cataract extraction by phacoemulsification with primary IOL implantation in at least one eye, were willing and able to return for routine follow-up, and who provided written informed consent were included.
Patients were excluded if they had (1) any ocular disease that could cause postoperative corrected distance visual acuity (CDVA) to be 20/40 or worse (eg, retinal disease); (2) hypotony, uncontrolled glaucoma, or a corneal implant; (3) blood or other material in the anterior chamber; (4) residual, recurrent, or active ocular or eyelid disease; (5) a history of lens or zonular instability; (6) contraindications to cataract surgery; or (7) previously undergone keratorefractive surgery, including LASIK or photorefractive keratectomy. Women who were pregnant, lactating, or planning to become pregnant during the course of the study were excluded. Also excluded were patients with intraoperative or postoperative adverse events or complications that could contribute to poor visual or refractive outcomes (eg, posterior capsule rupture, vitreous loss, or retinal detachment).
Patients were excluded during surgery if there was vitreous loss, anterior chamber hyphema, inability to control intraocular pressure, zonular or capsular rupture, bag–sulcus or sulcus–sulcus IOL placement, or unknown placement of the haptics or suturing of the primary incision.
Following application of topical or retrobulbar anesthesia and preoperative dilating drops, using each surgeon's standardized regimen, eyes in the no laser treatment group underwent cataract surgery using the phacoemulsification device alone. Standard manual techniques were used for anterior capsulotomy, lens phacofragmentation, and corneal incisions, with the digital marker M incision guide used for corneal incisions. The anterior capsule was opened by manual continuous curvilinear capsulorhexis with assistance of a digital marker M capsulorhexis guide to help ensure proper alignment (Figure A, available in the online version of this article). An Alcon AcrySof toric IOL was implanted with guidance from the digital marker M.
Example of an image of the digital capsulorhexis marker captured with the measurement module.
For eyes in the toric, monofocal, and multifocal groups, a disposable patient interface was mounted onto the distal end of the LenSx laser, which was lowered onto the patient's eye. A suction ring was applied to the eye concentric to the limbus. The digital marker L was used, followed by the LenSx laser procedure, including lens phacofragmentation, anterior capsulotomy, and/or corneal incision. The suction was subsequently released and the interface removed. Following phacoemulsification and aspiration, using the same phacoemulsification device used in the no laser treatment group and with the digital marker M as a guide, an AcrySof IOL was implanted into the capsular bag. Implants included toric IOLs (toric group), monofocal IOLs with paired arcuate incisions (monofocal group), and multifocal IOLs with paired arcuate incisions (multifocal group).
Measurements Using Image-Guided Planning System
Prior to surgery, all patients were evaluated for CDVA. Lenstar (Haag-Streit, Bem, Switzerland) and the VERION measurement module were used to measure the magnitude of astigmatism and the axis of astigmatism for eyes with cylinder of 0.75 D or greater, with the Lenstar data used for IOL planning and selection. Patients were evaluated using the vision planner. All patients underwent slit-lamp examination and measurements of intraocular pressure and corneal topography (ie, axis of corneal curvature). At 1 and 3 months postoperatively, manifest refraction, autorefraction, visual acuity (uncorrected, CDVA, and uncorrected near), intraocular pressure, and corneal topography were measured. Patients were again evaluated using the Lenstar and the VERION measurement module and vision planner and underwent slit-lamp examination. Keratometry readings from the VERION measurement module and the topographer (LenSx) were recorded at the preoperative visit and at 1 and 3 months postoperatively. Information collected included device type, steep and flat keratometry, steep and flat axis, magnitude of astigmatism, and actual toric placement axis. All adverse events were recorded.
The primary study objective was to determine the proportion of eyes with preexisting astigmatism achieving 0.50 D or less of residual refractive cylinder 3 months after implantation of toric IOLs or corneal incisions guided by the components of the image-guided system, as applicable to each arm of the study. The secondary objective was to determine the proportion of eyes with manifest refraction spherical equivalent (MRSE) deviating 0.50 D or less from the target outcome after 3 months.
The statistical objective was to evaluate the percentage of eyes in the four groups with a residual refractive cylinder of 0.50 D or less and MRSE deviation from the target refraction of 0.50 D or less at 3 months. Calculations showed that if the response rate was 50%, a sample size of 150 eyes at 3 months would provide a two-sided 95% confidence interval with a length of 0.08 (or 8%) from the center to the limit. Assuming a loss to follow-up rate of 5% at 3 months, 155 patients undergoing IOL implantation with the image-guided system in each study group would be necessary.
Within-group comparisons relative to baseline were determined by calculated two-sided 95% confidence intervals, based on binomial distributions. Because this study was non-randomized, between-group statistical comparisons were not performed.
All of the 422 eyes enrolled completed surgery. The study sites in Houston, Texas; Mt. Pleasant, South Carolina; Salt Lake City, Utah; Stillwater, Minnesota; and Nice, France, enrolled 161, 97, 55, 92, and 17 eyes, respectively. The safety analysis set, defined as all eyes of patients who provided informed consent and underwent cataract surgery, included 413 eyes. Four hundred eyes completed the 3-month visit and were included in the intention-to-treat analysis set, defined as all patients with at least one efficacy assessment in at least 1 eye at 1 and 3 months. A total of 384 eyes completed the study and were included in the per protocol analysis set, defined as all eyes in the intention-to-treat set that completed all study visits, did not violate inclusion/exclusion criteria, and were evaluated for primary efficacy at 3 months (Table 1).
Demographic and clinical characteristics of the study patients are shown in Table 2. Approximately two-thirds of patients in each group were female. Except for the monofocal group, most patients underwent surgery on both eyes. The Holladay II formula was used to calculate IOL power in more than 95% of eyes. Astigmatism characteristics of the eyes in the safety analysis set are shown in Table 3.
Demographic Characteristics of Study Patients (Safety Analysis Set)
Astigmatism Characteristics of the Safety Analysis Set
The primary objective of this study was residual refractive cylinder at 3 months; results for the intention-to-treat population are shown in Figure 1. Residual refractive cylinder of 0.50 D or less was achieved in 71.6% of eyes in the no laser treatment group, 74.5% of eyes in the toric group, 62.5% of eyes in the monofocal group, and 71.0% of eyes in the multifocal group. Based on a binomial distribution, residual refractive cylinder in each of the four study arms was significantly improved at 3 months relative to baseline. Mean ± standard deviation residual refractive cylinder in the no laser treatment, toric, monofocal, and multifocal groups was 0.451 ± 0.4519 D (range: 0.00 to 3.25 D), 0.384 ± 0.4279 D (range: 0.00 to 2.00 D), 0.497 ± 0.4002 D (range: 0.00 to 1.50 D), and 0.450 ± 0.3710 D (range: 0.00 to 1.50 D), respectively.
Residual refractive cylinder at baseline (preoperative) and at 3 months (postoperative) in astigmatic eyes in the intention-to-treat population that underwent intraocular lens (IOL) implantation. Eyes in the no laser treatment group were implanted with toric IOLs using the VERION system (Alcon Laboratories, Inc., Fort Worth, TX) and digital marker M (microscope), and eyes in the toric, monofocal, and multifocal groups were implanted with IOLs using the VERION system, LenSx laser, digital marker L (laser), and astigmatic keratotomy (for monofocal and multifocal groups). D = diopters; CI = confidence interval
The secondary objective of this study was MRSE accuracy to target at 3 months. The results of this analysis are shown in Figure 2. The percentage of eyes with an absolute deviation of 0.50 D or less from target refraction was high in all four groups: 69.6% in the no laser treatment group, 80.0% in the toric group, 77.3% in the monofocal group, and 82.0% in the multifocal group. The results in each of the four groups was significantly better than at baseline (P < .0001). Similarly, CDVA was significantly better at 3 months than at baseline in the four groups (Figure B, available in the online version of this article).
Manifest refraction spherical equivalent (MRSE) accuracies to target at baseline (preoperative) and at 3 months (postoperative) in astigmatic eyes in the intention-to-treat population that underwent intraocular lens (IOL) implantation. Eyes in the no laser treatment group were implanted with toric IOLs using the VERION system (Alcon Laboratories, Inc., Fort Worth, TX) and digital marker M (microscope), and eyes in the toric, monofocal, and multifocal groups were implanted with IOLs using the VERION system, LenSx VERION system, LenSx laser, digital marker L, and astigmatic keratotomy (monofocal and multifocal groups). D = diopters; CI = confidence interval
Corrected distance visual acuity (CDVA) at baseline in the safety analysis set and at 3 months in the intention-to-treat analysis set. (A) Eyes in the no laser treatment group were implanted with toric intraocular lenses (IOLs) using the VERION system (Alcon Laboratories, Inc., Fort Worth, TX) and digital marker M (microscope); and eyes in the (B) toric, (C) monofocal, and (D) multifocal groups were implanted with IOLs using the VERION system, LenSx, digital marker L (laser), and astigmatic keratotomy (monofocal and multifocal groups).
One serious ocular adverse event was reported for a patient who experienced a retinal tear, which was deemed unrelated to the image-guided system. One patient experienced a non-ocular serious adverse event. There were three reports of device malfunction, two of which were associated with LenSx sensor failure and one with LenSx suction. None of these device malfunctions resulted in harm to the patient.
Accurate positioning of a toric IOL to the intended alignment axis is critical for optimal outcomes in patients with cataract who have preexisting corneal astigmatism.1,4,5 Currently, several alignment options may be used by cataract surgeons to align toric IOLs at the intended axis or for arcuate or corneal relaxing incisions. Cataract surgeons commonly employ a manual three-step ink-marking procedure prior to the first incision. However, this preoperative technique is inherently prone to variability and limits the potential to reach a targeted outcome.1 Errors as small as 5° away from the axis of toric IOL placement in the eye may lead to a 17% error in intended correction.1 Thus, every degree of misalignment of the toric IOL implantation may induce a greater than 3% error in the anticipated treatment effect, with the final dioptric error influenced by the cylindrical power correction of the toric IOL implanted. Furthermore, the alignment error may be larger in individual cases due to fading of the ink markings, horizontal or vertical translocation of the ink marks, or even a complete washout of the ink marks at the time of surgery.6
To reduce errors associated with manually performed preoperative procedures and to improve cataract surgery outcomes, we used an image-guided surgical planning system that incorporates digital planning and surgical positioning tools. The digital imaging tool captures ocular surface measurements, including keratometry, and a digital image of the eye for intraoperative cyclorotation registration. The surgical planning software can identify and map preoperative characteristics and precisely calculate IOL power with alignment of suggested toric IOLs.
This multicenter study assessed the clinical utility of the image-guided surgical planning system for the treatment of patients with cataract who had preexisting astigmatism using toric IOL or corneal incisions. Residual refractive cylinder was measured 3 months after the implantation of toric IOL or corneal incisions. In addition, MRSE was measured at 3 months postoperatively.
Use of this system for implanting toric IOLs without the LenSx procedure resulted in achievement of 0.50 D or less of residual refractive cylinder at 3 months postoperatively in 71.6% of eyes. When the image-guided surgical planning system was used with the LenSx procedure, 74.5% of eyes achieved 0.50 D or less of residual refractive cylinder. A previous study7 showed refractive outcome variability among surgeons performing cataract surgery with A-constant optimization. In that study, the mean absolute residual refractive cylinder was 0.59 D for AcrySof toric IOLs and 1.22 D for AcrySof spherical control IOLs (P < .0001), with 53.3% and 23.6% of eyes, respectively, achieving residual refractive cylinder of 0.50 D or less.7
Use of the image-guided surgical planning system for implanting toric IOLs without the LenSx procedure resulted in a 3-month postoperative MRSE accuracy of 0.50 D or less to target in 69.6% of eyes. Use of the image-guided surgical planning system with the LenSx procedure for implanting multifocal IOLs resulted in 82.0% of eyes achieving 0.50 D or less of residual refractive cylinder.
At 3 months after surgery, 71.0% of eyes implanted with the multifocal IOLs plus astigmatic keratotomy using the image-guided system achieved 0.50 D or less of residual refractive cylinder, as did 62.5% of eyes implanted with the monofocal IOLs plus astigmatic keratotomy using the same system. Evaluations of 3-month postoperative MRSE accuracy to target showed that 77.3% of eyes implanted with monofocal IOLs and 82.0% of eyes implanted with multifocal IOLs using the image-guided surgical planning system with the LenSx procedure with astigmatic keratotomies achieved 0.50 D or less of residual refractive cylinder.
Safety results were good. No discontinuations from the treatment occurred due to adverse events and all adverse events were considered unrelated to study treatment. Most adverse events were mild and occurred most frequently in monofocal IOLs followed by toric IOLs. Dry eye was reported to be the most frequently occurring adverse event.
The limitations of this study include its non-random study design, the relatively small number of eyes studied, and the differences in A-constant among investigators, although A-constant affects spherical results only, not residual cylinder. Additional prospective randomized clinical studies may establish the clinical advantages of the image-guided surgical planning system over a manually performed three-step ink-marking diagnostic procedure for the treatment of preexisting astigmatism in patients with cataract with IOL implantation.
The study findings demonstrate that the image-guided surgical planning system is effective in guiding the surgeon to achieve accurate correction of preexisting astigmatism in patients undergoing refractive cataract surgery with IOLs. The refractive outcomes reported here with the use of the image-guided surgical planning system were consistent with previously reported studies showing refractive outcome variability among surgeons whose standard practice is to meticulously optimize their surgical planning using a manually performed three-step ink-marking diagnostic procedure for IOL implantation.
- Visser N, Berendschot TTJM, Bauer NJC, Jurich J, Kersting O, Nuijts RMMA. Accuracy of toric intraocular lens implantation in cataract and refractive surgery. J Cataract Refract Surg. 2011;37:1394–1402. doi:10.1016/j.jcrs.2011.02.024 [CrossRef]
- Popp N, Hirnschall N, Maedel S, Findl O. Evaluation of 4 corneal astigmatic marking methods. J Cataract Refract Surg. 2012;38:2094–2099. doi:10.1016/j.jcrs.2012.07.039 [CrossRef]
- Tjon-Fo-Sang MJ, de Faber JTHN, Kingma C, Beekhuis WH. Cyclotorsion: a possible cause of residual astigmatism in refractive surgery. J Cataract Refract Surg. 2002;28:599–602. doi:10.1016/S0886-3350(01)01279-2 [CrossRef]
- Abulafia A, Barrett GD, Kleinmann G, et al. Prediction of refractive outcomes with toric intraocular lens implantation. J Cataract Refract Surg. 2015;41:936–944. doi:10.1016/j.jcrs.2014.08.036 [CrossRef]
- Nguyen TM, Miller KM. Digital overlay technique for documenting toric intraocular lens axis orientation. J Cataract Refract Surg. 2000;26:1496–1504. doi:10.1016/S0886-3350(00)00442-9 [CrossRef]
- Osher RH. Iris fingerprinting: new method for improving accuracy in toric lens orientation. J Cataract Refract Surg. 2010;36:351–352. doi:10.1016/j.jcrs.2009.09.021 [CrossRef]
- Holland E, Lane S, Horn JD, Ernest P, Arleo R, Miller KM. The AcrySof Toric intraocular lens in subjects with cataracts and corneal astigmatism: a randomized, subject-masked, parallel-group, 1-year study. Ophthalmology. 2010;117:2104–2111. doi:10.1016/j.ophtha.2010.07.033 [CrossRef]
Description of Study Groups (Intention-to-Treat Set)
|No laser treatmenta||102||Toric||VERION only|
|Toricb||110||Toric||VERION + LenSx|
|Monofocalc||88||Monofocal + AK||VERION + LenSx|
|Multifocald||100||Multifocal + AK||VERION + LenSx|
Demographic Characteristics of Study Patients (Safety Analysis Set)
|Characteristic||No Laser Treatmenta (n = 70)||Toricb (n = 71)||Monofocalc (n = 71)||Multifocald (n = 65)||Total (N = 277)|
|Gender, n (%)|
| Male||24 (34.3)||28 (39.4)||25 (35.2)||19 (29.2)||96 (34.7)|
| Female||46 (65.7)||43 (60.6)||46 (64.8)||46 (70.8)||181 (65.3)|
|Age (y), mean ± SD||68.6 ± 9.41||68.8 ± 8.46||67.7 ± 7.50||65.6 ± 7.61||67.7 ± 8.34|
|Operated eye, n (%)|
| Right||16 (22.9)||11 (15.5)||34 (47.9)||15 (23.1)||76 (27.4)|
| Left||18 (25.7)||18 (25.4)||18 (25.4)||11 (16.9)||65 (23.6)|
| Both||36 (51.4)||42 (59.2)||19 (26.8)||39 (60.0)||136 (49.1)|
|Formula used for IOL power calculation, eyes, n (%)|
| Holladay I||0 (0)||1 (0.9)||0 (0)||2 (1.9)||3 (0.7)|
| Holladay II||106 (100.0)||96 (85.0)||89 (98.9)||102 (98.1)||393 (95.2)|
| SRK/T||0 (0)||14 (12.4)||1 (1.1)||0 (0)||15 (3.6)|
| Haigis||0 (0)||2 (1.8)||0 (0)||0 (0)||2 (0.5)|
|Axial length (mm), eyes|
| Mean ± SD||24.182 ± 1.4472||24.166 ± 1.3746||24.140 ± 1.5197||24.150 ± 1.2420||24.160 ± 1.3910|
| Range||21.52 to 28.85||21.27 to 27.61||21.44 to 29.07||20.66 to 27.95||20.66 to 29.07|
|Keratometry astigmatism (D) (steep – flat), eyes|
| Mean ± SD||1.645 ± 1.2305||1.822 ± 1.0035||0.885 ± 0.2665||0.947 ± 0.3994||1.352 ± 0.9416|
| Range||0.29 to 9.69||0.09 to 5.72||0.23 to 1.63||0.22 to 2.55||0.09 to 9.69|
Astigmatism Characteristics of the Safety Analysis Set
|Astigmatism (D), n (%)||No Laser Treatmenta (n = 106)||Toricb (n = 113)||Monofocalc (n = 90)||Multifocald (n = 104)||Total (N = 413)|
|≤ 1.00||27 (25.5%)||16 (14.2%)||61 (67.8%)||65 (62.5%)||169 (40.9%)|
|1.01 to 1.50||38 (35.8%)||31 (27.4%)||28 (31.1%)||27 (36.0%)||124 (30.0%)|
|1.51 to 2.00||19 (17.9%)||29 (25.7%)||1 (1.1%)||9 (8.7%)||58 (14.0%)|
|> 2.00||22 (20.8%)||37 (32.7%)||0 (0.0%)||3 (2.9%)||62 (15.0%)|