Introduction

Since the introduction of modern surgical microscopes in the 1940s, these devices have been central to practices in cataract surgery1,2. Recent years have seen significant advancements in the field, including surgical techniques, phacoemulsification machine designs, and intraocular lens technologies3. First introduced in 19994, the three-dimensional heads-up display system (3D HUDS) is one of the burgeoning innovations. It is increasingly used by ophthalmologists in the last two decades and enhances visualization of surgical fields by projecting the view to a 3D monitor5,6.

3D HUDS-based ophthalmic surgery is reported to offer several advantages: better ergonomics for surgeons, enhanced depth perception and visualization of peripheral surgical field, reduced phototoxicity, and improved teaching opportunities7,8,9,10,11,12,13. 3D HUDS offer similar safety and efficiency as the traditional binocular microscope8,14,15. However, reported potential limitations include possible time lags, financial costs, the need for additional operating room space, a slow learning curve, and longer surgical times during early uses6,7,16. Nonetheless, experienced cataract surgeons typically adapt to this tool after 25–50 cases, after which there are no differences in the surgical times or complication rates17.

Whereas the conventional ophthalmic surgical microscopes with its binocular viewing systems require surgeons to adapt their posture to get to the eyepieces, 3D HUDS allow surgeons more unrestricted and natural postures18 (Fig. 1). Therefore, the system enables the surgeon to operate in “heads-up” position; a more neutral body position and move freely without compromising image quality. 3D HUDS users reported improved musculoskeletal symptoms10,13, suggesting adopting this new technology provides opportunities for better ergonomics for ophthalmologists.

Figure 1
figure 1

Schematic drawing of (A) 3D heads-up display system and (B) conventional operating microscope, illustrating heads-up posture and forward-head posture, respectively.

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Optimizing ergonomics in surgery is crucially important, impacting both the productivity and career longevity of surgeons, which must not be overlooked19. Unfortunately, work-related musculoskeletal disorders are a prevalent issue among ophthalmologists worldwide, with an increased prevalence associated with more time spent in surgery20,21,22,23,24. Eye care providers report a higher prevalence of musculoskeletal pain compared to family medicine physicians due to repetitive tasks and awkward working positions, underlining the need for workplace modifications25. Neck, back, and shoulder pain are frequently reported10,26.

Artevo® 800 (Carl Zeiss Meditec, Jena, Germany), a digitally integrated 3D microscope, has demonstrated its efficacy and safety through years of experiences15. It provides a real-time stereoscopic view of the surgical field on a wide-screen 4 K monitor, offering true colors, improved resolution, enhanced depth of focus, and excellent visualization15,17.

Previous studies on the ergonomic differences associated with the use of 3D heads-up display systems (3D HUDS) have primarily relied on survey data, resulting in inherently subjective outcomes9,10,13. To date, few studies have quantitatively assessed the intraoperative body positions of ophthalmologists. This study aimed to quantitatively evaluate the neck positions and musculoskeletal discomfort of surgeon during cataract surgery when using Artevo® 800, in comparison to a conventional binocular microscope.

Methods

This study was conducted in compliance with the principles dictated in the Declaration of Helsinki and was approved by the Institutional Review Board (IRB number: P01-202,405-01-027) of the Ministry of Health and Welfare, Republic of Korea. All patient data were treated anonymously following privacy regulations. The requirement for written informed consent was waived because of the study design and utilization of unidentified data.

This is a single-center, comparative observational case-series study conducted at Fatima Eye Clinic, Changwon, Korea, an ophthalmology-dedicated clinic staffed by four full-time ophthalmologists. The study included consecutive patients older than 40 years with uncomplicated cataracts who were scheduled for routine phacoemulsification surgery between August 11, 2023 and November 7, 2023. Exclusion criteria were patients with a history of previous intraocular surgery, coexisting vision-threatening diseases such as wet age-related macular degeneration or corneal diseases that compromise transparency, cataracts with significant subluxation or phacodonesis. Data of patients who underwent cataract surgery on both eyes were analyzed separately.

Data collected from patients included age and sex, preoperative best-corrected visual acuity (BCVA) and spherical equivalent (SE), postoperative BCVA at the 1-month visit, and the severity of cataracts according to Lens Opacities Classification System (LOCS III). BCVA measurements were taken using the Snellen chart and later converted to the logarithm of the minimum angle of resolution(logMAR) scale for analysis. Operation times were recorded, measuring from the start of corneal incision to the removal of the microscope from the surgical field.

Data collected from the surgeon included neck angles and Visual Analog Scale (VAS) scores. The Cervical Range of Motion (CROM) device (Performance Attainment Associates, Minnesota, USA) is designed to measure cervical range of motion in the three cardinal planes (Fig. 2). The CROM device was worn by the surgeon to measure neck position during active periods of surgical procedures. Neck angle was estimated by reading the scale, to the nearest 1°, on the temporally located inclinometer of the device to assess the degree of neck flexion or extension, during continuous curvilinear capsulorhexis (CCC), phacoemulsification, and intraocular lens (IOL) placement. Measurements were taken by a third observer in the operating room when the surgeon’s position was kept stable. Positive angles indicate flexion, while negative angles indicate extension. The device was calibrated at the start of each day. After each surgery, the surgeon immediately recorded VAS score to assess subjective postoperative musculoskeletal discomfort. On this scale, a score of 0 represents no discomfort at all and a score of 10 represents the worst possible discomfort.

Figure 2
figure 2

Image showing operation room with Artevo® 800 (Carl Zeiss Meditec, Jena, Germany) and three-dimensional heads-up display system.

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Data collection was done by a single surgeon experienced in using both 3D HUDS and conventional binocular microscope. The clinic’s operating room was equipped with two microscopes during the study period: Artevo® 800 and Opmi Lumera® 700 microscope (both from Carl Zeiss Meditec, Jena, Germany). Artevo® 800 provides 3D HUDS, while Opmi Lumera® 700 is a conventional microscope with oculars for viewing. A 55-inch 3D monitor supported on a movable cart was used for display with Artevo® 800 (Fig. 3).

Figure 3
figure 3

Image showing the Cervical Range of Motion device (Performance Attainment Associates, Minnesota, USA).

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The surgeon was positioned at lateral side of the patient and made a clear corneal incision on the temporal side. Cataract operations were performed under topical anesthesia using the Centurion Vision System (Alcon, Fort Worth, Texas, USA) phacoemulsification machine for all patients. The surgeries were performed using the two types of microscopes in alternating sequence throughout the study period.

Statistical analysis

Continuous variables were presented as mean ± standard deviation and categorical variables were reported as frequency (percentage). Group differences were assessed using Student’s t-test or the Mann–Whitney U test when the normality assumption was not met, or the chi-square test for categorical variables. All tests were two-tailed, with a p-value < 0.05 considered statistically significant. Statistical analyses and generation of graphs were performed using Microsoft Excel 2021 (Microsoft, Los Angeles, California, USA), IBM SPSS version 26.0 (IBM Corp, Chicago, Illinois, USA), and GraphPad Prism version 6 (GraphPad Software, San Diego, California, USA).

Results

A total of 80 cataract surgeries (50 patients) were included in this study, with 40 surgeries performed using Artevo® 800 and another 40 using Opmi Lumera® 700. No intraoperative complications, such as nucleus drop, radial tear, or requirement of anterior vitrectomy, were observed in any of the 80 cases. Although Artevo® 800 is equipped with both 3D HUDS and conventional eyepieces, allowing for intraoperative conversion, no conversions to the binocular viewing system were necessary during the surgeries performed with Artevo® 800.

Baseline patient characteristics associated with each microscope are presented in Table 1. There were no significant differences in laterality, age, preoperative logMAR BCVA, preoperative SE, or the proportion of dense nuclear cataracts between two groups. A higher proportion of female patients was observed in Artevo® 800 group (65.0% vs. 37.5%, p = 0.014).

Table 1 Baseline patient characteristics.
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Intraoperative and postoperative patient outcomes are detailed in Table 2. Postoperative logMAR BCVA at 1 month was 0.033 ± 0.117 for 3D HUDS and 0.021 ± 0.048 for the conventional microscope, with no significant difference (p = 0.972). Surgical times were 597 ± 90 s for Artevo® 800 and 600 ± 150 s for Opmi Lumera® 700, also with no significant difference (p = 0.430). Postoperative SE was not included due to inconsistent target diopters.

Table 2 Intraoperative and postoperative outcomes in the Artevo® 800 and Opmi Lumera® groups.
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Neck angles measured during surgeries with Artevo® 800 were predominantly negative, indicative of neck extension, whereas measurements taken Opmi Lumera® 700 were generally positive, indicating neck flexion. Significant differences in neck angles were observed during CCC, phacoemulsification, and IOL placement (− 8.18 ± 2.85° vs. 8.27 ± 2.93° in CCC, − 7.83 ± 3.30° vs. 8.87 ± 2.83° in phacoemulsification, − 7.43 ± 3.80° vs. 7.67 ± 3.73° in IOL placement, respectively, with all p < 0.001). The mean absolute neck angle was calculated as the absolute value of the average of these three measurements to represent the magnitude of neck deviation, regardless of direction (flexion or extension). The mean deviation from neutral neck position did not show a significant difference (7.80 ± 2.83 vs. 8.29 ± 2.88, p = 0.362).

Box plots representing neck angles are shown in Fig. 4. For Artevo® 800, the interquartile ranges (IQR) were − 10.00° to − 7.25° for CCC, − 10.00° to − 6.25° for phacoemulsification, and − 10.00° to − 3.25° for IOL placement. These did not overlap with the IQRs for Opmi Lumera® 700, which were 8.00–10.00° for CCC, 8.00–11.00° for phacoemulsification, and 7.00–10.00° for IOL placement.

Figure 4
figure 4

Box and whisker plot of neck angles in continuous curvilinear capsulorhexis(CCC), phacoemulsification, intraocular lens(IOL) placement with Artevo® 800 and Opmi Lumera® 700. Lines on each box plot represent minimum, first quartile, median, third quartile, and maximum.

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The postoperative VAS scores were significantly lower for surgeries conducted with Artevo® 800 (1.27 ± 0.55 vs. 1.73 ± 0.64, p < 0.001). No cases with VAS score equal to or greater than 4 were reported. The distribution of VAS scores is shown in Fig. 5.

Figure 5
figure 5

Histogram showing distribution of the VAS score with Artevo® 800 and Opmi Lumera® 700.

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Discussion

The use of slit lamps, indirect ophthalmoscopes, surgical loupes, surgical microscopes, and computers place stress on the shoulders, neck, and back of ophthalmologists. This stress results from poor posture and repetitive movements during ocular examinations and surgeries, which are considered modifiable risk factors27. Several reviews emphasize the necessity for ergonomic adjustments and provide guidelines for addressing these factors in operating rooms, including practical recommendations27,28,29 (Fig. 6).

Figure 6
figure 6

Schematic drawing of optimal ergonomic position.

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This study used basic patient data, neck angles measured with the CROM device, and VAS scores to compare intraoperative and postoperative outcomes, surgeon’s postures and musculoskeletal discomfort in cataract operations performed with either 3D HUDS or a conventional microscope. It differs from previous reports in that it is one of the first to investigate the ergonomic differences of 3D HUDS using quantitative measurements taken during individual surgeries.

Surgical times, visual acuity outcomes, and intraoperative complications did not differ between the two groups, aligning with findings from previous studies14,17. According to the assumptions in the same study, the comparable surgical times in the two groups suggest that the surgeon had completed the learning curve for 3D HUDS17.

Neck angles were predominantly flexed, with a mean value of 7.80°, when using conventional microscopes with oculars, and extended, with a mean value of 8.29°, when using 3D HUDS. In both cases, deviation from neutral point was minor, mostly less than 10°. Neck flexion in conventional microscope is due to the design of the microscope, necessitating leaning forward to peer into the oculars. Conversely, 3D HUDS enable surgeons to maintain a more upright posture, as they focus on the 3D monitor positioned in front of them.

Experience with 3D HUDS in terms of image quality, neck strain, and eye strain can be influenced by factors such as viewing tilt angle, monitor distance and height, chair height, and laterality of the eye30. For endoscopic procedures in rhinology, it is recommended that monitors be placed directly in front of the surgeon, between 80 and 120 cm from the surgeon’s eyes, and at or below eye level31,32,33. Although these recommendations may not directly apply to ophthalmic surgeries using 3D HUDS, they highlight the importance of proper monitor placement.

To the best of our knowledge, there is no established consensus on the optimal positioning of the display in 3D HUDS. In one study on cataract surgery using 3D HUDS, the average eye-to-monitor distance was 170 cm, and a closer monitor (distance of 127–140 cm) caused less eye strain30. Optimal distance and height vary with different displays, and the perception of 3D dimensionality differs among observers, suggesting the need for individualized settings for optimal results34. In our study, we measured the eye-to-monitor distance to be between 140 and 150 cm. The floor-to-monitor height (measured from the floor to the central point of the display) was 135 cm. However, these measurement were not consistently taken and likely varied slightly, as the monitor often needed to be moved according to the laterality of the operating eye. Optimizing the eye-to-monitor distance and the monitor height according to the surgeon could help achieve a neutral neck position, potentially eliminating the minor degree of neck extension observed in this study.

The VAS is an appropriate and valid tool for clinical use, exhibiting good inter-test and test–retest reliability35,36. However, its efficacy has primarily been studied for evaluating patient pain, and multiple-question reporting systems have been reported to provide superior assessment37,38. The VAS is a self-reporting tool, and it is unfeasible to conceal the type of microscope used during operations from surgeons. Therefore, the VAS results were susceptible to bias.

The CROM device allows noninvasive measurement of neck angles and is a reliable clinical tool used in many studies to assess neck movements39,40. However, one limitation is that it can only measure at a single moment and cannot record changes over time. Additionally, this study did not include neck rotation or lateral bending into analysis. While the CROM device provides reliable measurements of forward head posture, it requires additional components and steps41, limiting its use during active surgical performance.

This study reported reduced postoperative discomfort with the use of 3D HUDS, compared to conventional microscopes. The load on the cervical spine increases progressively with the degree of flexion; tilting the neck forward by 15 degrees increases the load by 2.5 times relative to a neutral position42. For ophthalmologists who suffer from leaning forward and forward head posture when using conventional microscopes, 3D HUDS is expected to provide a greater benefit. We hypothesized that 3D HUDS promote a neutral body and neck position, potentially decreasing musculoskeletal discomfort for surgeons. However, although neck flexion was eliminated with the use of 3D HUDS, neck extension with a similar absolute degree of deviation from the neutral point was still observed. From these findings, the improvement in postoperative discomfort cannot be fully explained by changes in neck angle alone. It could be attributed to other ergonomic benefits, such as the resolution of hunched back, correction of forward head posture, and enabling free movement without the need to remain fixed to the microscope oculars. Additionally, one study recently demonstrated that conventional microscopes cause more fatigue in the sternocleidomastoid and upper trapezius muscles compared to 3D HUDS in vitreoretinal and phacoemulsification surgeries43. A survey of Japanese ophthalmologists showed 72% had a neutral neck posture and 61% had a neutral back position with 3D HUDS, compared to 34% and 33% with conventional microscopes, respectively44.

This study, along with recent studies on ergonomic benefits of 3D HUDS10,43,44, reinforces that 3D HUDS is effective for improving surgeon ergonomics and reducing musculoskeletal discomfort. However, there are a few points to consider before strongly advocating for the use of 3D HUDS for ergonomic purposes. Ergonomic positions could also be achieved, at least partially, by other methods such as use of ocular extenders, moving the oculars 20–25° toward the surgeon, or timely re-adjusting the patient’s head position27,28. Additionally, 3D HUDS faces its own ergonomic challenges, such as extra neck tilting due to the viewing system being positioned above the patient’s head, which impedes an exact straight-line position relative to the surgeon, and awkward head rotation for the assistant positioned perpendicularly to the operating surgeon45,46.

There are several limitations to acknowledge in this study. First, there was no standardized setting for the operating rooms, which may have influenced the surgeon’s positions during surgery with 3D HUDS, such as monitor height or distance. Additionally, the assessment of the surgeon’s position and musculoskeletal discomfort relied on relatively simple methods. Other methods used in ergonomic studies to measure muscular burden or assess movements, if extended to fields other than ophthalmology, include myotonometer, electromyography, inertial measurement unit sensors, and Rapid Entire Body Assessment43,47,48,49,50. Other tools, such as the NASA Task Load Index and the Borg scale, are also reported for assessing the perceived exertion of surgeons30,48. Lastly, the study included only a single surgeon, and positioning with conventional microscopes and 3D HUDS can vary individually44.

In conclusion, we quantitatively measured neck angles and assessed postoperative musculoskeletal discomfort in cataract surgery to compare 3D HUDS and conventional microscopes. Our results suggest that adopting 3D HUDS can resolve neck flexion during surgery and alleviate ophthalmologists’ postoperative musculoskeletal discomfort. Further studies investigating intraoperative ergonomic positions and measuring surgeon fatigue, involving multiple ophthalmologists, are warranted.