The Use of 3D Visualization in Micro-Invasive Glaucoma Surgery

Anterior segment surgical procedures address eye disorders from the cornea, conjunctiva, iridocorneal angle, iris, and lens.

Visualization is paramount for surgical success in any operation including pterygium excision, penetrating keratoplasty, cataract removal, placement of minimally invasive glaucoma devices, iris repair, or combined specialty cases.

Supplemented with coaxial illumination and extended depth of focus, the modern-day microscope evolved into an irreplaceable commodity for visualization. However, in recent years the improvements in optical quality, illumination, and depth of field have begun to plateau.

Concurrently, significant limitations continue to exist such as prolonged exposure of the retina to excess illumination, linear dependency on visible light for visualization, limited performance in high-magnification, and potential for surgeon fatigue due to operating room ergonomic conditions.

While digital visualization was quickly adopted by the posterior segment surgeons given the increased depth of focus, greater magnification, and precise focus, augmenting measured and delicate maneuvers, the anterior segment surgeons are beginning to appreciate the conferred benefits to their respective surgeries.

In addition to an improved binocular disparity, reserved almost exclusively for digital platforms, one can expect an improved light intensity profile, better data integration to heads-up-display (HUD) from surgical suite, less dependence on stains to highlight structures, and an equivocal high-volume efficiency setup.

Minimally invasive glaucoma surgery (MIGS) is a rapidly and continually evolving sector within anterior segment ophthalmology.

Filling the gap between medical management and large incisional surgical therapies, MIGS relies heavily on intraoperative visualization to identify small anatomic features to either place devices or make targeted cuts for successful outcomes.

To obtain adequate visualization using a traditional microscope, most MIGS setups requires the surgeon to rotate the microscope 35 degrees towards the operator, rotate the patients head 35 degrees away, and the surgeons chair will need to be lowered and shifted away from the patient, ultimately requiring the surgeon to extend her/his arms to reach the operative field.

When coupled with a handheld gonioscopy lens, the surgeon is able to overcome the total internal reflection optics induced by the cornea, in order to visualize the angle.

The use of the trabecular bypass concept via trabeculectomy or aqueous shunts for the surgical treatment of glaucoma has advanced over time, with the goal of providing more reliable, less invasive control of intraocular pressure.

In a study evaluating the trends of glaucoma surgeries in Medicare Patients from 1994-2017, the use of new microinvasive glaucoma surgery (MIGS) has rapidly increased, now accounting for a significant majority of glaucoma surgeries.

MIGS refers to procedures that include the following 5 characteristics: ab interno approach, minimal disruption of normal anatomy, high safety profile, good efficacy, and fast recovery time. These include various stenting and trabecular meshwork excision procedures, as well as Excimer LASER Trabeculostomy (ELT).

Proper visualization of the angle is a critical feature of successful MIGS procedures. Access to the trabecular meshwork for MIGS procedures is via the anterior chamber using a clear corneal incision.

Light passing through a medium with a higher index of refraction (cornea) into one with a lower index of refraction (air) results in an angle of refraction that is larger than the angle of incidence, leading to internal reflection of light; as a result, the use of direct surgical gonioscopy overcomes total internal reflection, and therefore allows visualization of the angle.

Although the use of intraoperative gonioscopy has a steep learning curve, it is a necessary tool to perform microinvasive glaucoma surgery. Surgical visualization can be compromised if proficient bimanual technique with a goniolens is suboptimal.

Typical maneuvers to achieve visualization of the angle structures with MIGS procedures using the standard operating microscope include the need to rotate the patient’s head away by 35 degrees, as well as the need to rotate the microscope 35 degrees towards the surgeon.

This results in the surgeon’s need to extend the arms to perform the necessary surgical maneuvers while also needing to maintain the eyes at the oculars to see the procedure. This non-physiologic position can result in ergonomic strain.

That ergonomic strain is exaggerated for the surgical assistant whose head often needs to be tilted along with the microscope. In the last 50 years, the innovation applied to the standard operating microscope has been limited to enhancements in optics or to improvements in its light source.

Despite these updates, limitations, such as dependence on oculars and linear dependency on visible light for visualization can lead to the potential for surgeon fatigue due to operating room ergonomic conditions as well as prolonged light exposure to the retina and limited performance and range of depth with extremes of high-magnification.

When it comes to surgical visualization, there has been no real paradigm shifting technology to address these issues. However, these limitations can actually be addressed using available digital technology.

Some of the benefits of digital technology used to improve visualization for cataract surgery can also assist visualization during MIGS procedures.

Digital video capability has undergone tremendous, rapid advancements in frame rate, pixel count and resolution, dynamic range, and latency over the past 20 years. Furthermore, the use of 3D digital visualization systems in ophthalmic surgery are certainly not new.

Weinstock and colleagues are the first to describe the feasibility of using 3D digital visualization during anterior segment surgery back in 2009.

Weinstock also recently studied the NGENUITY 3D Digital Visualization System (Alcon Vision, LLC; Fort Worth, TX; USA) and demonstrated similar safety and efficiency between 3D visualization and the traditional binocular microscope.

NGENUITY is a real-time digital image guidance system utilizing an ultra-highdefinition 3D flat-panel OLED display.

Using digital visualization with the NGENUITY platform at maximum system magnification, an aperture setting of 30% open, and a viewing distance of 1.2 meters results in an up to 48% increased magnification, up to 5x extended depth of field and up to 42% finer depth resolution (stereopsis) when compared to analog microscopes.

Data on the use of 3D digital visualization for MIGS is slowly increasing. Ohno in Japan reported his findings when using the NGENUITY 3D Visualization System with surgical navigation for cataract surgery as well as iStent (Glaukos Corporation; San Clemente, CA; USA) placement in 2019.

He postulated that the extended depth of field under high magnification experienced when using 3D visualization would be beneficial for angle inspection using a gonioprism.

He ultimately found that the extended depth of field at high magnification and heightened stereoscopic attributes provided by 3D digital visualization, unlike when using the conventional microscope, reduced the need for frequent focusing adjustments when used for trabecular microbypass stent implantation.

A specific benefit of the increased range of depth in angle surgery is that the surgeon is able to insert an injector or blade through the corneal wound while still being in focus on angle structures.

Palácios studied the experience of Brazilian vitreoretinal surgeons who used 3D heads-up display (NGENUITY) for visualization compared to the operating microscope; MIGS cases (iStent placement) were included.

Overall, image resolution, depth perception, field of view, ergonomics, and educational value were significantly better using 3D heads-up display as compared to the operating microscope.

Concerning specifically the MIGS cases, only the 3D camera coupled to the microscope required tilting, as it was unnecessary to tilt the patient’s head position; according to the authors, this led to enhanced patient and surgeon comfort.

Furthermore, a wider viewing angle was achieved using the 55-inch 4K display. With NGENUITY, the aspects of visualization mentioned above are superior for the surgeon, and equally good for all other members of the OR team.

In an academic center, this improved view has allowed all surgeons learning MIGS to notice details not otherwise noticeable with two-dimensional screens.

The level of detail observed is evidenced by the types of comments made, about the positioning of glaucoma stents, the difference in stent sheen in the anterior chamber versus in Schlemm canal, and the location of blood reflex in stenting and trabecular meshwork excision procedures.

Furthermore, surgical training for new procedures is facilitated with NGENUITY, as surgical instructors or industry partners are able to better guide the surgeon through the initial challenges of a new procedure.

The fact that the surgeon’s view is exactly the same as everyone else in the OR allows for an improved and accelerated knowledge transfer process. Finally, engagement of the nursing team with NGENUITY is unparalleled, as they appreciate details not otherwise noticeable on the two-dimensional screen.

It is not uncommon for nurses that have spent decades in the ophthalmology OR to comment that they had never appreciated the various steps of surgery as much as when observing the 3D images through their passive polarized glasses.

Their increased engagement allows them to be more involved in the surgery and better anticipate next steps and therefore what instruments the surgeon needs.

Ergonomics are critical for comfort during a surgical day, for surgeon longevity and for injury prevention. The ability to sit more comfortably without the need to come towards the microscope leads to better positioning, and less neck and back strain.

It is especially useful for the assistant in angle surgery, who is otherwise forced to tilt their head significantly to align themselves with the tilted microscope during angle visualization.

The pandemic has also highlighted the interest in maintaining distance between the surgeon and the patient, and between members of the healthcare team.

NGENUITY allows for this distance while maintaining the surgical view with improved ergonomics. The capacity to digitally enhance the surgical view will likely allow for modifications that can minimize the impact of the blood reflex and also emphasize the pigmentation of the trabecular meshwork.

Similar to digital enhancements specific to retinal surgery that have improved the surgical experience and safety profile, future digital enhancements for MIGS surgery may allow for better angle visualization and MIGS performance.

NGENUITY for MIGS is in its infancy and the future is, therefore, very exciting. Overall, beyond the visualization benefits of NGENUITY for cataract surgery, NGENUITY also contributes to a better experience in the OR for MIGS procedures.

Better three-dimensional visualization of angle structures, reduced light exposure, engagement and unification of the entire OR team, improved capacity to educate, and ergonomic positioning are all features of NGENUITY that improve the OR experience, and ultimately patient outcomes.