Enhancing visibility and efficiency in toric intraocular lens surgery with the pivot technique and an assistant-mounted guidance system

Mounting a guidance system on the assistant microscope achieves comparable IOL rotational stability vs standard mounting, avoids surgical field dimming, and statistically shortens surgical time, improving surgical efficiency.

Abstract

Purpose:

To evaluate surgical outcomes and visibility when mounting the Verion guidance system on the assistant microscope compared with the main microscope during toric intraocular lens (IOL) implantation.

Setting:

ASUCA Eye Clinic, Sendai, Miyagi, Japan.

Design:

Experimental study and retrospective observational study.

Methods:

The influence of the Verion guidance system on surgical field image quality was evaluated in porcine eyes through luminance analysis in ImageJ. The clinical study included 201 eyes with grade 2 nuclear cataracts. Axis marking was performed with the guidance system mounted on the assistant microscope using the pivot technique (pivot group; n = 105) or on the main microscope using the conventional technique (conventional group; n = 96). The primary outcome was IOL rotational stability at 3 months postoperatively. Secondary outcomes included surgical time, visual acuity, and refractive results.

Results:

The guidance system significantly reduced overall image brightness (mean luminance: 55.4 ± 15.4 vs 84.8 ± 17.7) and obscured fine details. The pivot and conventional groups had no significant difference in absolute toric IOL misalignment at 3 months (P = .819). Surgical time was shorter in the pivot group (226.8 ± 105.4 seconds vs 233.6 ± 119.2 seconds; P = .024). Postoperative visual and refractive outcomes were comparable (P > .05) with no serious complications.

Conclusions:

The pivot technique achieved comparable IOL rotational stability and visual outcomes vs the conventional method. By circumventing light reduction induced by the guidance system, the pivot technique represents a safe, useful, and efficient alternative in toric IOL implantation.

Approximately one-third of patients undergoing cataract surgery have corneal astigmatism, with 22% having ≥1.5 diopters (D) and 8% having ≥2.0 D.^1,2 Toric intraocular lenses (IOLs) have become the standard method for correcting corneal astigmatism of ≥0.75 D during cataract surgery, but its efficacy fundamentally depends on its precise alignment with the intended corneal meridian.^3,4 Misalignment can significantly compromise astigmatic correction, with approximately 10% of the cylindrical correction effect lost for every 3 degrees of rotation off the target axis.^5,6

Traditional manual marking techniques have an average IOL alignment error of 5 degrees, attributed to factors such as poor mark visibility and human error.^7,8 Accordingly, the Verion Image-Guided System (Alcon Laboratories, Inc.) emerged as a significant advancement that achieved superior accuracy vs conventional manual marking.^9,10 Using the Verion guidance system can significantly decrease IOL misalignment, as confirmed in previous clinical studies.^11,12 The guidance system comprised a reference unit that captures a high-resolution image of the eye and a digital marker that provides real-time surgical guidance, compensating for cyclotorsion and tracking eye movements.^13,14 However, because the guidance system involves capturing light information, it inherently attenuates the light passing through the attached microscope. This reduction in light theoretically limits the surgeon's view, although this has not been previously quantified. Accordingly, we developed the pivot technique, wherein the guidance system is mounted on the assistant microscope. This assistant scope is initially used to view the toric guide for marking, and then, the surgeon pivots the microscope turret 90 degrees to perform the remainder of the surgery through the main microscope, which is free of the light-dampening guidance system (Figure 1). This facilitates precise, digitally guided marking while maintaining optimal visibility during surgery.

Figure 1.

The pivot technique. A: The assistant microscope is rotated 90 degrees toward the surgeon for toric axis confirmation and marking with the guidance system. B: The assistant microscope is then pivoted back 90 degrees and the main microscope for the remainder of the surgery.

Although previous studies have evaluated guidance systems mounted on the main surgical microscope, the effectiveness of mounting it on an assistant microscope remains unexplored.^15,16 Accordingly, this study quantitatively evaluated the extent to which a guidance system degrades the surgical image, as well as compared the clinical outcomes of toric IOL implantation between 2 different guidance system configurations. The safety and utility of our new pivot technique (pivot group), wherein the guidance system is mounted on the assistant microscope, was compared with the conventional approach of mounting the system on the main microscope (conventional group).

METHODS

This study included an experimental part using porcine eyes and a retrospective observational part involving human participants. The study was approved by the institutional review board (approval no. 32; July 20, 2025) and adhered to the tenets of the Declaration of Helsinki. Owing to the retrospective nature of the study, the requirement for written informed consent was waived by the institutional review board. Patients were given the choice to opt out of participation through information provided through the institutional bulletin board and website. Since the study was conducted outside the United States, HIPAA regulations do not apply.

Experimental Study

Porcine eyes were obtained from Sendai Central Meat Wholesale Market, Sendai, Japan, within 6 h of enucleation. The experimental protocol using animal tissue was reviewed and approved by the Institutional Animal Care and Use Committee of ASUCA Eye Clinic SENDAI (approval no. 33; July 20, 2025). All procedures adhered to the Association for Research in Vision and Ophthalmology Statement for the Use of Animals in Ophthalmic and Vision Research. Eyes were stored at 4°C and used within 24 h of procurement. An 8:2 beam splitter (Carl Zeiss Meditec AG) was attached to a Lumera 700 assistant microscope (Carl Zeiss Meditec AG). A high-resolution smartphone camera (iPhone 16 Pro Max, Apple Inc.) was mounted through a microRec adapter (microRec GmbH). Unprocessed RAW images (dng file format) were captured using the Lightroom application camera (Adobe Systems, Inc.). Microscope illumination was set to the maximum (100%) with a halogen light source, using 70% oblique and 30% coaxial illumination. To simulate the surgeon's view, 2 sets of images were acquired in rapid succession using the same porcine eye under identical conditions: one without the Verion guidance system attached (MID−), followed by one with it attached (MID+) (Supplemental Figure 1, available at http://links.lww.com/JRS/B572). Digital images were acquired in an 8-bit grayscale format (256 gray levels, ranging from 0 [black] to 255 [white]). Mean pixel intensity values were measured using ImageJ software (v. 1.54, National Institutes of Health). A circular region of interest with a diameter of 6 mm was placed within the pupil area. Histograms were generated with pixel count on the vertical axis and intensity on the horizontal axis. Results are expressed as mean gray values (dimensionless) on a scale of 0 to 255.

Clinical Study

This retrospective observational study evaluated clinical outcomes after phacoemulsification with toric IOL implantation using 2 different guidance system mounting methods.

Participants

The study included patients with Emery-Little grade 2 nuclear sclerosis who underwent 2.2 mm clear corneal incision cataract surgery and received a toric IOL at the ASUCA Eye Clinic between March 2024 and November 2024. The conventional group included a final cohort of 96 patients who underwent surgery with the guidance system mounted on the main microscope (ie, the standard method). The pivot group included a final cohort of 105 consecutive patients who underwent surgery between December 2024 and April 2025 with the guidance system mounted on the assistant microscope. The exclusion criteria for both groups were as follows: a history of ocular trauma; a planned postoperative refraction of ±0.5 D or greater; poor mydriasis precluding postoperative toric axis measurement; any systemic or ocular conditions potentially compromising capsular bag stability, including collagen disorders, pseudoexfoliation syndrome, chronic uveitis, and glaucoma; previous intraocular surgery (eg, vitrectomy); the need for a capsular tension ring; and any intraoperative complications.

Intraocular Lens

All implanted IOLs were Clareon monofocal Toric models (Alcon Laboratories, Inc.) with an A-constant of 119.1. The Clareon Toric IOL, available in models T2 to T9, is capable of correcting approximately 0.65 to 4.0 D of corneal astigmatism.

Surgical Technique

All surgeries were performed by a single experienced surgeon using the guidance system to display the axis for toric IOL alignment. In the conventional group, the Verion guidance system was attached to the main microscope, which was used for axis marking and during the remainder of the surgery. The pivot technique was used in the pivot group, wherein the guidance system was attached to the assistant microscope. Specifically, the pivot technique begins with rotating the assistant microscope (with the Verion guidance system attached) 90 degrees toward the surgeon to mark the toric axis. The microscope is then rotated back 90 degrees to its original position. The remainder of the procedure was completed using the main microscope with no guidance system attached (Figure 1). The pivot technique requires a microscope equipped with a dual optical port, a compatible beam splitter, and a rotatable turret.

A single side-port was created alongside a 2.2 mm clear corneal incision. A continuous curvilinear capsulorhexis (∼5.0 mm diameter) was made using 27-gauge forceps. Hydrodissection was performed, followed by phacoemulsification, then irrigation and aspiration of the remaining cortex. The capsular bag was inflated with sodium hyaluronate 1% (Healon, Santen Pharmaceutical Co., Ltd.), and the IOL was implanted in the bag without enlarging the incision. The toric IOL was rotated to align its marks with the steepest meridian of corneal astigmatism. The ophthalmic viscosurgical device was completely aspirated, taking care to avoid IOL rotation. After stromal hydration of the incisions, the final IOL meridian position was confirmed. All surgeries were performed using the CENTURION phacoemulsification system (Alcon Laboratories, Inc.).

IOL Power Calculation and Toric Meridian Determination

IOL power for all toric IOLs was calculated using measurements from the IOLMaster 700 (Carl Zeiss Meditec AG), using the Barrett Universal II formula for power determination. Toric power was calculated using the total keratometry values for corneal curvature and the axial length from the IOLMaster 700. The Alcon toric calculator was used, and the IOL with the smallest absolute error was implanted. The Verion guidance system was used for guidance.

Outcome Measures

For the experimental study, the images were qualitatively and quantitatively compared. A histogram was created for the brightness of a selected region, measured using ImageJ.

For the clinical study, all patients were examined preoperatively and at 3 months postoperatively. Preoperative evaluation included IOL power, axial length, and flat and steep keratometry measured through the IOL Master 700. The type of astigmatism was also recorded and classified based on the degree of the steep meridian: with-the-rule astigmatism (60 to 120 degrees), against-the-rule astigmatism (0 to 30 degrees or 150 to 180 degrees), and oblique astigmatism (30 to 60 degrees or 120 to 150 degrees).

The ASCRS Astigmatism Double-Angle Plot Tool was used to plot the magnitude and meridian of postoperative subjective residual astigmatism at 3 months.¹⁷ Surgical time (ie, from the start of marking until complete wound closure) and cumulative dissipated energy were recorded based on the CENTURION report.

Postoperative Evaluation

Corrected distance visual acuity (CDVA) and subjective and objective refractive values were assessed up to 3 months postoperatively. Toric axis deviation was measured through a dilated examination at 3 months postoperatively. The axis position was confirmed through retroillumination during slitlamp examination. The amount of rotation was calculated as the difference from the intended axis, with positive and negative values indicating clockwise and counterclockwise rotation, respectively. Absolute rotation was also calculated. Visual acuity values were converted to the logMAR scale for statistical analysis.

Statistical Analysis

Normality was assessed using the Shapiro-Wilk test. Homogeneity of variances was evaluated using the Brown-Forsythe and Levene tests. The t test was used for normally distributed data with equal variances, while the Welch t test was used for data with unequal variances. The Mann-Whitney U test was used for nonnormally distributed data. A power analysis was conducted on the 3-month absolute axis misalignment. With α = 0.05, power = 80%, and group sample sizes of 105 (SD = 8.5) and 96 (SD = 9.1), the minimum detectable effect size was 3.50 degrees. Categorical variables (eg, sex, operative eye, astigmatism type, and IOL model) were analyzed through the Fisher exact test or the chi-squared test. Statistical analysis was performed using JMP Pro (v. 18.2.1, SAS Institute, Inc.), with P value less than 0.05 considered statistically significant.

RESULTS

Experimental Study Results

MID− and MID+ images from the porcine eye experiment were qualitatively compared, revealing that the MID+ image was noticeably darker overall (Figure 2A and B). On examining the fine structure of the lens surface, fine lines were blurred and indistinct in the MID+ image but were clearly delineated in the MID− image (Figure 2C and D, arrows). The iris color was light brown in the MID− image, but it appeared as a darker brown in the MID+ image with reduced contrast with the pupillary margin. Similarly, the sclera in the MID+ image was also slightly darker and more yellow compared with the MID− image, indicating a difference in color temperature. Brightness analysis revealed a mean brightness of 84.8 ± 17.7 for MID− vs 55.4 ± 15.4 for MID+, with the brightness histogram for MID+ exhibiting a significant shift toward lower values (Figure 3).

Figure 2.

Qualitative comparison of the surgical field view with and without the guidance system. A, C: Without the guidance system (MID−) and (B, D) with the guidance system (MID+). The upper panels (A, B) demonstrate the overall view, which is darker in MID+. The lower panels (C, D) are magnified views of the lens surface, demonstrating that fine structures (arrows) are less distinct in MID+ (D) vs MID− (C).

Figure 3.

Brightness histogram with and without the guidance system. Brightness distribution was obtained from the porcine eye surgical field image. Horizontal axis, intensity value (0 to 255); vertical axis, pixel count. With the guidance system attached (MID+), the histogram is shifted toward the lower intensity side.

Clinical Study Results

A total of 201 eyes (conventional group, 96 eyes: 57 right eyes, 39 left eyes; pivot group, 105 eyes: 60 right eyes, 45 left eyes) were included. Patient demographics are summarized in Table 1. The conventional group had significantly greater preoperative flat keratometry, steep keratometry, and subjective cylinder power (all P < .001), whereas there were no significant differences in age (P = .578) or axial length (P = .909).

Table 1.

Patient demographics and baseline characteristics

Characteristic	Pivot group (n = 105)	Conventional group (n = 96)	P value
Eyes (n)	105	96	—
Right/left eye	60/45	57/39	.776
M/F	51/54	52/44	.468
Age (y)	72.6 ± 8.4	72.8 ± 9.2	.578
AL (mm)	23.9 ± 1.4	24.0 ± 1.2	.909
Kf (mm)	7.66 ± 0.27	7.83 ± 0.22	<.001*
Ks (mm)	7.46 ± 0.29	7.60 ± 0.22	<.001*
Preop cylinder (D)	−0.95 ± 1.08	−1.27 ± 1.09	<.001*
IOL power (D)	18.9 ± 4.4	20.0 ± 3.6	.053
Preop corneal cylinder type			.147
WTR	50 (47.6)	33 (34.4)
ATR	40 (38.1)	48 (50.0)
Oblique	15 (14.3)	15 (15.6)
Toric IOL model			.956
T2	22 (21.0)	20 (20.8)
T3	47 (44.8)	36 (37.5)
T4	20 (19.0)	27 (28.1)
T5	9 (8.6)	6 (6.3)
T6	2 (1.9)	2 (2.1)
T7	1 (1.0)	1 (1.0)
T8	2 (1.9)	3 (3.1)
T9	2 (1.9)	1 (1.0)

AL = axial length; ATR = against-the-rule; D = diopters; IOL = intraocular lens; Kf = flat keratometry; Ks = steep keratometry; M/F = male/female; WTR = with-the-rule

Data shown as mean ± SD or n (%)

^*Statistically significant (P < .05)

Surgical time was modestly but significantly shorter in the pivot group than in the conventional group (226.8 ± 105.4 vs 233.6 ± 119.2 seconds; mean difference: 6.8 seconds, P = .024; 95% CI: 0.9-12.7 seconds), while cumulative dissipated energy values were not significantly different (3.64 ± 2.69 vs 4.50 ± 4.20, P = .066).

At 3 months postoperatively, the pivot and conventional groups were comparable in absolute toric IOL misalignment (7.13 ± 8.52 vs 7.38 ± 9.05 degrees, P = .819) and signed axis misalignment (−1.84 ± 10.97 vs −1.39 ± 11.62 degrees, P = .357) (Figure 4). The centroid of the prediction error on the double-angle plot was 0.02 ± 0.32 D @ 152 degrees for the pivot group and 0.12 ± 0.47 D @ 114 degrees for the conventional group, with both located near the origin (Figure 5). There were no serious intraoperative or postoperative complications in either group.

Figure 4.

Toric IOL rotation at 3 months postoperatively. Box-and-whisker plots show the IOL rotation at 3 months. The top and bottom of the box represent the third and first quartiles, respectively. The line inside the box is the median, while the whiskers represent the maximum and minimum values. A, Absolute rotation; B, distribution of rotation (clockwise: positive, counterclockwise: negative). There was no significant difference between the groups.

Figure 5.

Double-angle plot of residual astigmatism at 3 months postoperatively. The residual astigmatism vector is plotted relative to the prediction. Each point represents an individual eye, and the red dot represents the centroid (vector mean). Blue ellipse, 95% CI. A: Pivot group and (B) conventional group.

No significant differences were found in uncorrected distance visual acuity, CDVA, subjective spherical equivalent, and subjective cylinder values (all P > .05).

DISCUSSION

This study experimentally evaluated the impact of a guidance system on surgical field visibility, as well as compared the clinical performance of different mounting configurations for toric IOL implantation. In an experiment using porcine eyes, the conventional mounted guidance system quantitatively reduced the brightness of the surgical field and impaired the delineation of fine details. On clinical review, the pivot technique (ie, mounting the guidance system on the assistant microscope) achieved IOL rotational stability and visual outcomes that were comparable with the conventional method (ie, mounting on the main microscope), with modestly reduced surgical time.

Uniquely, this study quantitatively demonstrated the optical impact of the guidance system. The microscope images were captured as digital negative files (dng files), which record the raw light information from the camera sensor without processing, thereby enabling the evaluation of optical effects. This information is analogous to the light stimulus perceived by the surgeon's eyes, which can serve as an objective measure of the distinct darkening of the surgical field and decrease in resolution. This reduced visibility possibly contributes to surgeon fatigue and stress in the conventional method.

Clinically, the degree of IOL rotation at 3 months was similar between both groups, indicating that both techniques can achieve good IOL positional stability. Thus, the toric guidance system can effectively ensure accurate axis marking, even when mounted on the assistant microscope.

The pivot technique is performed entirely within the sterile field of the microscope, ensuring proper infection control. Surgical time was statistically significantly shorter in the pivot group (difference: 6.8 seconds, P = .024). Although this may not represent a meaningful efficiency improvement, it confirms that the pivot technique does not result in substantial prolongation of surgical time despite the additional steps of microscope rotation and refocusing. The improved visibility likely enhanced the efficiency of precise maneuvers such as capsulorhexis, nucleus division, and fine cortical aspiration. This finding is clinically relevant because it demonstrates that the potential benefits of improved surgical field visibility can be achieved without compromising operative efficiency.

These results support the effectiveness of guidance systems, consistent with reports by Titiyal et al. and Khatib et al. who also found superior outcomes with the Verion guidance system vs manual marking.^15,16 Moreover, the centroids for both groups in our study were favorable compared with previous reports. Preoperative corneal astigmatism was significantly higher in the conventional group, which could be related to the nonsignificant trend of slightly higher postoperative subjective astigmatism in the same group. This baseline difference could also be attributed to the different study periods for the 2 cohorts, which should be considered when interpreting the results.

The comparable postoperative outcomes between groups, despite the significantly higher preoperative astigmatism in the conventional group, suggest that both techniques can effectively manage varying degrees of corneal astigmatism. However, this baseline difference limits the direct comparison of the 2 methods and should be considered when interpreting these results.

A potential disadvantage of the pivot technique is the extra step of rotating the microscope and the nonintuitive direction of X–Y axis movement through the foot switch when marking while using the assistant microscope. Nevertheless, the marking was generally completed quickly, with no cases requiring fine X–Y adjustments.

The key finding of this study is that the assistant microscope mounting method had comparable outcomes with the conventional main microscope method, potentially even improving surgical efficiency because it bypasses the reduced light conditions caused by the guidance system.

This study is limited by its retrospective design and the lack of random patient allocation. In addition, it is possible that the 2 groups were enrolled at different times and that trends in the degree of astigmatism among patients receiving for toric IOLs may have changed over time, leading to differences between the groups. Future prospective, randomized controlled trials are needed for a more comprehensive evaluation. In addition, in this study, the pivot technique was performed using the Lumera 700 microscope, which is equipped with a coaxial assistant microscope. Further investigation is required for microscopes without a coaxial field of view. This study measures the reduction in light caused by the guidance system, but it does not include any subjective feedback on surgeon comfort, visual fatigue, or brightness.

In conclusion, this study demonstrated the safety and efficacy of mounting the Verion guidance system on the assistant microscope during toric IOL surgery. This new method maintains the clinical performance of the conventional main microscope mounting method while improving surgical efficiency.

WHAT WAS KNOWN

• During toric IOL implantation, guidance systems are conventionally mounted on the main microscope, providing superior accuracy vs manual marking.

• The main microscope-mounted setup is the standard and most studied method.

• The accuracy of toric IOL alignment directly affects the effectiveness of astigmatism correction.

WHAT THIS PAPER ADDS

• Mounting the guidance system on the assistant microscope (ie, the pivot technique) can achieve comparable IOL rotational stability and visual outcomes with the standard main microscope-mounted method.

• The pivot technique statistically shortens surgical time, potentially improving surgical efficiency.

• The guidance system significantly reduces the brightness of the surgical field, but this can be circumvented by using the pivot technique.