Three-Dimensional Heads-up Display in Cataract Surgery: A Review : The Asia-Pacific Journal of Ophthalmology

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Review Article

Three-Dimensional Heads-up Display in Cataract Surgery: A Review

Muecke, Thomas P.*,†; Casson, Robert J. DPhil, FRANZCO*,†

Author Information
Asia-Pacific Journal of Ophthalmology: November/December 2022 - Volume 11 - Issue 6 - p 549-553
doi: 10.1097/APO.0000000000000562
  • Open

Abstract

Continued improvements in optics and electronics over the past few decades have culminated in modern ophthalmic surgical microscopes (OSM) that currently serve as a powerful, trusted tool in cataract surgery.1 However, recent advancements in digital image processing and enhancement have raised the possibility of using 3-dimensional heads-up display (3D HUD) systems for the visualization of the ophthalmic surgical field.

These systems were first used in posterior segment surgery,2 however, in recent years, several studies have demonstrated their efficacy and safety in anterior segment procedures, including cataract surgery.3 The NGENUITY 3D Visualization System (NGENUITY; Alcon Inc., Fort Worth, TX) was the first commercially available 3D HUD for ophthalmic surgery. NGENUITY is a modular system equipped with 2 high dynamic range cameras mounted onto an OSM.4 The 2 cameras capture images from the OSM, and a high-speed central processor generates a stereoscopic image that is displayed on a high-definition large screen 3D monitor.3–5 The surgeon wears 3D polarized glasses to obtain stereopsis,6 and performs surgery viewing the 3D monitor in a heads-up position rather than with a slightly flexed neck position at the OSM eyepieces.7

In this review, we report the emerging evidence supporting the use of 3D HUD visualization in cataract surgery, its limitations, and future directions.

ADVANTAGES OF 3D HUD-BASED CATARACT SURGERY

Improved Ergonomics

Long-term use of the OSM can increase the cataract surgeon’s risk of work-related musculoskeletal injury.2,8–10 In contrast, the heads-up position granted in 3D HUD visualization is reported to reduce the strain on the surgeon’s cervical and lumbar spine.2,11 Although it is difficult to quantitatively assess the effect of OSM ergonomics on cataract surgeons’ musculoskeletal complaints, several studies9,10,12,13 have obtained qualitative survey-based data. Tan et al10 reported that of 245 ophthalmologists, 81.4% reported musculoskeletal pain, discomfort, or disability, which was commonly exacerbated by surgery. Furthermore, 9.6% suffered from reduced working hours and 1.2% eliminated surgery from their practice altogether.10 Weinstock et al12 studied the musculoskeletal complaints of 25 anterior segment surgeons: 77% reported that 3D HUD reduces the severity and frequency of their musculoskeletal pain. The surgeons included in this study, however, had varying weekly surgical volume and 3D HUD cataract experience.12 Bin Helayal and colleagues unexpectedly reported similar musculoskeletal pain levels between 140 3D HUD and OSM ophthalmic surgeons. The 3D HUD users, however, had a significantly higher surgical load per week than the OSM users.13 In addition, surgeons with less 3D HUD cataract surgery experience may report discomfort due to unfamiliarity and the associated learning curve. Kelkar and colleagues studied the first 100 3D HUD cataract surgeries of 2 surgeons, who reported that their comfort improved significantly over consecutive cases. It was concluded that an experienced cataract surgeon, without prior experience using 3D HUD, should be able to adapt to 3D visualization after 50 cases.9 However, these observational studies are limited by recall bias. Prospective research should aim to quantify the improvement in musculoskeletal symptoms of cataract surgeons when transitioning from OSM to 3D HUD.

Educational Benefit

3D HUD visualization provides improved teaching opportunities for trainee cataract surgeons and enhanced operating room teamwork. 3D HUD provides the opportunity for trainees to experience the same 3D view of the surgical field as the surgeon.11,13,14 Furthermore, data and optical coherence tomography imaging can be overlaid onto the 3D monitor without obstructing the surgical view.9,14 Surgery can also be recorded and rewatched on the 3D HUD system, as well as streamed through 5G for telementoring.3,15 3D HUD visualization systems may expedite junior cataract surgeon training and may limit complications for patients.1

The 3D HUD monitor also grants operating theater staff a better surgical view. This is likely to foster teamwork and promote a better understanding of the surgery so that the next procedural steps can be anticipated.6 Furthermore, theater staff training is potentially accelerated and improved.

Several studies2,4,13 utilized questionnaires to determine the subjective educational benefit of 3D HUD cataract surgery compared with OSM. Del Turco and colleagues reported that 10 (83%) of their responders believed that 3D HUD provided a greater teaching potential than OSM. This was consistent with the findings of Wang et al,2 who reported that, on average, 26 medical interns and 39 medical students significantly preferred the educational benefit of 3D HUD. On a scale of 1–10, the average reported educational value for 3D HUD and OSM was 9.42±0.81 and 8.06±1.25, respectively.2 In addition, Bin Helayel et al13 concluded that 49 (68.1%) ophthalmic surgeons reported that 3D HUD was a valuable educational tool and 60 (83.3%) recommended its use in surgical training. The surgeons included in this study, however, were mainly vitreoretinal surgeons (81.9%).13

Importantly, some surgeons did not score parameters including teaching benefit in favor of 3D HUD visualization due to its associated complexity, novelty, and learning curve.

Depth Perception and Peripheral Visualization

While depth of field can decrease at higher magnifications in OSM cataract surgery, it is preserved in 3D HUD visualization without inducing any optical distortions.14,16 It is also reported that the NGENUITY system allows for intraocular structures to be visualized with a 42% increase in depth resolution.3 In addition, the surgeon’s peripheral visual field is extended to a width not possible for the OSM.4 This improved depth of field and peripheral visualization allows for a larger perceived operating field.3,16

Several studies2,4,13 have provided evidence in support of improved depth perception in 3D HUD visualization compared with the OSM. Del Turco et al4 described that 9 of 12 cataract surgeons reported comparable or improved visibility and depth perception over OSM. Bin Helayel and colleagues utilized an online questionnaire to explore the opinions of 149 ophthalmic surgeons. It was reported that the anterior segment surgeons included in the study believed that 3D HUD performed better than OSM in terms of peripheral acuity and depth perception.13 Similarly, Wang and colleagues reported the responses of 65 participants’ satisfaction of depth perception on a scale of 1–10. The average score for 3D HUD and OSM visualization was 9.40±0.81 and 6.51±1 1.5, respectively.2

Digital Enhancement of the Surgical View

OSM visualization requires high illumination levels for sufficient visualization of intraocular structures. Prolonged light exposure during both anterior and posterior segment surgeries can result in retinal phototoxicity.17,18 While the short duration of cataract surgery significantly reduces the risk of retinal phototoxicity, repeated asymptomatic light exposure has been correlated with the pathogenesis of age-related macular degeneration and retinal dystrophies.17–19 Furthermore, high illumination may contribute to decreased comfort and cooperation of patients under topical anesthesia.14 3D HUD limits illumination delivered through the OSM to the patient’s retina. While reduced illumination would typically reduce visualization, images displayed on the 3D HUD monitor can be digitally enhanced to be 23 times brighter than what is seen through the OSM.14 Furthermore, image clarity, quality, and contrast are maintained.7,18,19

Several studies7,18,19 compared the intraocular illumination required in 3D HUD and OSM cataract surgery. Vélasque and colleagues reported a significant reduction in light intensity during 73 consecutive 3D HUD cataract surgeries. The reported mean delivered light intensity was 15±11.3% of the maximal.18 Nuclear cataracts (63% of the sample) only required a mean delivered light intensity of 9.6±5.4%.18 Similarly, Matsumoto et al7 reported that in 72 cases of 3D HUD cataract surgery, only 2% of the maximal main light output through the OSM and 6% of maximal retroillumination was required. For 5 cases, however, the retroillumination output had to be increased to 7% to 8% to improve visibility.7 Rosenberg and colleagues compared the illumination required for femtosecond laser-assisted cataract surgery (FLACS): 24 cases utilized OSM visualization and 27 cases utilized 3D HUD. It was reported that 3D HUD FLACS required 18.5±1.5% light intensity, whereas OSM FLACS required 43.4±3.7%.19 Furthermore, Matsumoto et al,7 Velasque et al,18 and Rosenberg et al19 reported no intraoperative complications in 3D HUD cataract surgery at the lower illuminance. This demonstrates that 3D HUD cataract surgery at a reduced illumination maintains a comparable safety profile to OSM.

Prospective studies should compare the conscious patient’s intraoperative comfort between 3D HUD and OSM cataract surgery.18 In addition, the short-term and long-term iatrogenic light induced outcomes of patient’s undergoing cataract surgery should be evaluated.

COMPARING THE INTRAOPERATIVE SAFETY OF 3D HUD-BASED AND OSM-BASED CATARACT SURGERY

Several studies1,2,19,20 reported the complication rates during 3D HUD and OSM FLACS. Rosenberg and colleagues and Wang and colleagues studied 51 and 117, eyes, respectively. Rosenberg and colleagues reported no complications for either the 3D HUD or OSM group, while Wang and colleagues reported one 3D HUD FLACS case complicated by intraoperative floppy iris. The small sample size described in Rosenberg and colleagues and Wang and colleagues, however, limits the interpretation of the study. Arguably, there are equivalently low complication rates in cataract surgery using either the OSM or the 3D HUD.

Weinstock and colleagues and Bedar and Kellner20 described the complication rates in both 3D HUD and OSM FLACS and phacoemulsification cataract surgery. Weinstock and colleagues studied a larger sample of 1225 eyes undergoing FLACS (separated into 870 3D HUD and 355 OSM) and 1095 undergoing phacoemulsification (separated into 803 3D HUD and 292 OSM). For the FLACS group, Weinstock and colleagues reported 6 (0.69%) complications for the 3D HUD group and 3 (0.84%) complications for the OSM group. For the phacoemulsification group, 6 (0.75%) complications were reported in the 3D HUD group and 2 (0.68%) complications in the OSM group.1 The complications reported for their sample included only posterior capsular rupture and vitreous prolapse.1 While the sample was unevenly split into the 2 groups, there was reported to be no significant difference in complications between the 3D HUD and OSM groups.

Bedar and Kellner20 reported 8 complications (0.8%) for the OSM group and 7 (0.7%) for the 3D HUD group. Bedar and Kellner20 did not distinguish which complications resulted from FLACS and which from phacoemulsification cataract surgery. The complications encountered predominantly comprised of capsule ruptures, with 6 occurring in the OSM group and 4 in the 3D HUD group.20 In addition, 2 iris prolapses and 1 zonular dialysis occurred in the 3D HUD group.20

Several studies4,9,11,16,21 reported the complication rates during 3D HUD and OSM phacoemulsification cataract surgery. Nairai and colleagues and Qian and colleagues reported no complications in either group; however, this may be attributed to their relatively smaller sample sizes of 91 and 20 eyes, respectively.

Kelkar et al9 studied a sample of 343 consecutive cases, with 100 cases undergoing 3D HUD cataract surgery: 6 (2.47%) complications occurred in the OSM group, and 2 (2.00%) occurred in the 3D HUD group. The surgeon self-reported visualization issues in 9 of the 100 3D HUD cases: 5 were due to illumination difficulties and 4 were due to poor depth perception.9 Of these 9 cases, the surgeon switched to OSM in 7 cases to manage the complications.9 Interestingly, of these 9 cases with visualization difficulties, 3 cases of low illumination and 2 cases of poor depth perception were reported in the first 25 3D HUD surgeries.9 In addition, the 2 complications encountered in the 3D HUD group, one zonular dialysis and the other nucleus drop, occurred within the surgeon’s first 50 cases. Zero occurred in the second 50 cases.9 In addition, 4 of the 7 switches to OSM to manage complications occurred in the first 50 cases. This demonstrates that a cataract surgeon may adapt to the alternative 3D HUD experience after approximately the first 50 cases. Once this learning curve is overcome, rates of complications may reduce.9

Del Turco and colleagues evenly distributed their sample into 2 groups: 1580 cases underwent 3D HUD phacoemulsification and 1598 underwent OSM phacoemulsification. Del Turco and colleagues reported 25 (1.58%) complications for the 3D HUD group, and 30 (1.88%) complications for the OSM group. The specific complications encountered, and their management was not described.4

Sandali et al16 assessed for the common postoperative complication of corneal oedema following 3D HUD phacoemulsification in 134 patients. Corneal edema can delay recovery and can cause patient dissatisfaction on the first day postoperatively.16

The results described that, when compared with OSM, patients undergoing 3D HUD cataract surgery with shallow anterior chambers <3 mm had lower levels of day 1 postoperative corneal swelling and better day 1 visual acuity.16 Specifically, they reported reduced postoperative central corneal thickening in the 3D HUD group: 17.3 μm±3.2 compared with 44.0 μm±9.3 with the OSM.16 Sandali and colleagues described that this may be attributed to the increased depth perception using 3D HUD visualization.

Several studies1,2,4,9,11,19–21 reported low rates of complications and no significant difference in complication rates between 3D HUD-based and OSM-based cataract surgery. In addition, as indicated in Table 1, surgical duration was comparable between 3D HUD and OSM. We therefore consider the 3D HUD visualization of FLACS and phacoemulsification cataract surgery to be equivalent to OSM in terms of safety profile. To ensure clinical robustness, however, future work should utilize large-scale multicenter studies to assess the complication rates of multiple surgeons with varying experience in 3D HUD cataract surgery. Short-term and long-term postoperative complications should also be described in addition to intraoperative complications.

TABLE 1 - Overview of Studies Comparing the Complication Incidence and Surgical Duration of 3D HUD and OSM Cataract Surgery
References Cataract Surgery Method Sample Size Sample Mean Age (y) 3D HUD Visualization System Surgical Duration (s) Complications
Bedar and Kellner20 FLACS, phacoemulsification Total: 2000 3D HUD group: 1000 OSM group: 1000 NGENUITY 3D HUD group: 703.8 OSM group: 710.4 3D HUD group: 8 OSM group: 7
Weinstock et al1 FLACS, phacoemulsification Total: 2320 3D HUD group: 1673 OSM group: 647 71.49±8.99 NGENUITY 3D HUD group: 388.8±69 OSM group: 391.2±82.8 3D HUD group: 12 OSM group: 5
Rosenberg et al19 FLACS Total: 51 3D HUD group: 24 OSM group: 27 73.3±8.9 NGENUITY 3D HUD group: — OSM group: — 3D HUD group: 0 OSM group: 0
Wang et al2 FLACS Total: 242 3D HUD group: 117 OSM group: 125 69.50±12.1 NCVideo 3D HUD group: 462.03±80.36 OSM group: 452.13±76.63 3D HUD group: 1 OSM group: 0
Kelkar et al9 Phacoemulsification Total: 343 3D HUD group: 100 OSM group: 243 66.1±7.0 Artevo 3D HUD group: 504±126 OSM group: 390±108 3D HUD group: 2 OSM group: 6
Nariai et al21 Phacoemulsification Total: 91 3D HUD group: 45 OSM group: 46 68.5±9.2 NGENUITY 3D HUD group: 239 OSM group: 228 3D HUD group: 0 OSM group: 0
Qian et al11 Phacoemulsification Total: 20 3D HUD group: 10 OSM group: 10 67±5.2 NGENUITY 3D HUD group: 498±104 OSM group: 542±88.6 3D HUD group: 0 OSM group: 0
Del Turco et al4 Phacoemulsification Total: 3178 3D HUD group: 1580 OSM group: 1598 NGENUITY, Artveo 3D HUD group: — OSM group: — 3D HUD group: 25 OSM group: 30
Sandali et al16 Phacoemulsification Total: 134 3D HUD group: 59 OSM group: 75 NGENUITY 3D HUD group:   OSM group: — 3D HUD group: — OSM group: —
3D HUD indicates 3-dimensional heads-up display; FLACS, femtosecond laser-assisted cataract surgery; OSM, ophthalmic surgical microscope.

LIMITATIONS OF 3D HUD-BASED CATARACT SURGERY

While the findings demonstrate that 3D HUD provides some benefits in ergonomics, educational value, depth perception, and intraocular illumination, and has a safety profile comparable to OSM, the learning curve is a disadvantage of a 3D HUD. Cataract surgeons with less experience using 3D HUD visualization systems may experience a learning curve whilst they adapt to the slight latency and visualization modifications.20 In 3D HUD cataract surgery, there exists a latency between the surgical maneuvers and the image that appears on the 3D monitor.9,22 This may be more evident in cataract surgeries, as surgical instruments move at a higher speed through the anterior segment than the posterior segment.2 During sophisticated movements, this latency might lead to mistakes and confusion.2,14 The NGENUITY and ARTEVO 3D HUD visualization systems currently report a latency of 70–80 ms22 and 50 ms,9 respectively. In addition, surgeons adapting to the change in depth perception, peripheral acuity, and the dissociation between their hands and eyes when in the upright HUD position, may contribute to the slow learning curve of 3D HUD.

As surgeons gain experience and familiarity with 3D HUD, their approval for it may increase.2 Kaur et al14 note that a surgeon with more prior cataract surgery experience may adapt more rapidly to the dynamics of the 3D HUD visualization system. As indicated by Kelkar et al,9 complications and satisfaction improved over consecutive 3D HUD cataract surgeries. Recognizing issues with the learning curve, current 3D HUD systems provide the surgeon an option to shift to OSM intraoperatively if they encounter a technical difficulty or challenging complication.14 Prospective research could explore the effect of the learning curve in 3D HUD cataract surgery by describing the performance and complication rates of surgeons with varying levels of experience using a 3D HUD visualization system. In addition, the self-reported surgeon satisfaction at different stages of the learning curve should be described.

3D HUD systems provide a platform for further potential improvements. Vocal commands may allow for switching of augmented color channels, digital gain, and light intensity for optimal visualization during specific surgical steps.18 Artificial intelligence and augmented reality technologies such as LIDAR could be incorporated into the high dynamic range cameras for 3D mapping of intraocular architecture, which can then be projected onto the 3D HUD monitor.6 This could further assist the surgeon in orientation and depth perception23 and could enable easy targeting of intraocular tissue and enhancement of specific structures.18

CONCLUSIONS

The evidence-based literature on 3D HUD cataract surgery remains relatively scarce, but it appears to have a comparable safety profile to OSM visualization. This is demonstrated by the low incidence of complications reported and no significant difference in complication rates between 3D HUD and OSM based cataract surgery. In addition, 3D HUD cataract surgery poses potential benefits, including improved ergonomics, educational benefit, and enhanced intraocular depth perception and visualization at low illuminance. Large-scale prospective studies are required to further demonstrate the safety of 3D HUD cataract surgery with emphasis on the effect of the surgeon’s learning curve on complication rates. In addition, the subjective impressions of enhanced ergonomics, educational benefit, and depth perception should be quantified.

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Keywords:

three-dimension; 3D; heads-up display; cataract surgery

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