The first robotic gonio surgery system was developed in the heat of the pandemic in 2020 by the ophthalmology innovation team at New York Eye and Ear Infirmary of Mount Sinai in New York, New York. 

This novel surgical system could dramatically improve outcomes for patients with glaucoma with its remarkable level of precision that is unachievable during standard glaucoma surgery.

The glaucoma module of the system is the first surgical application outside retina for the Preceyes robotic system, which was first CE marked in 2019 in Europe and is heading toward FDA studies in the United States.

Sean Ianchulev, MD, MPH, a professor of ophthalmology at the Icahn School of Medicine and director of ophthalmic innovation and technology at New York Eye and Ear Infirmary of Mount Sinai, pointed out that the robotic system allows surgeons to achieve precision during glaucoma surgery that is 1 to 2 μm, compared with what can be accomplished during a manual surgery.

“This is [approximately] a 20 to 40 times increase over existing levels of surgical precision,” Ianchulev said.

Previously, this system was used in Europe for retinal surgeries such as membrane peeling. It is now being developed for anterior segment application with the minimally invasive glaucoma surgery (MIGS) robot-assisted goniotomy and for stent implantation.

One of the greatest limitations of manual surgeries is surgeon tremor, which can average, during manual vitreoretinal surgery, a 182 root-mean-square tremor amplitude, with approximately a 100-μm peak-to-peak vector of magnitude. 

To emphasize this impact on a glaucoma surgery, Ianchulev explained that in Schlemm's canal the structures can be as small as 100 μm to 150 μm.

“When considering MIGS, we are at a new inflection point of precision where devices such as microstents and anatomic structures (eg, trabecular meshwork) are exceedingly small and require a much higher fidelity of surgical intervention,” Ianchulev said. “With the help of robotics, we can improve precision from approximately 120 μm to 150 μm down to approximately 5 μm.”

In a significant number of cases, micro-stents are often implanted outside the targeted and clinically relevant anatomy, which nullifies their IOP-lowering effect. Ianchulev related the case of one of his patients with glaucoma who had been considered to have well-controlled IOP following stent implantation. A follow-up evaluation showed that the stent had been positioned well below the trabecular meshwork.

“It was successfully deployed but anatomically and clinically inconsequential and not in the desired location,” Ianchulev said.

The increased precision of robotic surgery is important because of the need to improve the outcomes of glaucoma surgeries. Ianchulev said precision is the answer because of the problems that can arise during glaucoma surgeries such as malpositioning of stents and postoperative complications such as hypotony. With greater precision come greater surgical gains, he noted.

In fact, approximately 30% of MAUDE safety reports in the FDA iStent (Glaukos) database are related to malpositioning, likely aﬀecting both the safety and eﬃcacy of the procedure.

The investigators started by adapting the robotic retina technology for use in glaucoma surgeries to attempt goniotomy and stent implantation. The ﬁrst step was building an adaptation from 3D printing for the coupling between the iStent injected device and the robot to ensure successful surgeries.

Ianchulev described the challenges of developing this technology. One such challenge was adapting the angle of approach that was needed for visualization for robotic entry into the anterior chamber. Another was developing the real parameters necessary to operate the high-precision device in the angle using a joystick.

Ianchulev and Gautam Kamthan, MD, in collaboration with the Preceyes robotics team in the Netherlands, were able to demonstrate in a synthetic eye that robotic-assisted goniotomy can be successfully performed in a very controlled way.

“This really attested to the lack of tremor and high precision when operating this device. There was almost zero tremor,” Ianchulev said.

In like fashion, the team demonstrated precise robotic deployment of the iStent microstents with superior tremor-free manipulation and accurate precise implantation into the trabecular meshwork of the synthetic model.

“This is so important because this level of surgical precision has been unattainable before and it is unknown what the outcomes will be a result. This will transform surgical instrumentation to facilitate our new surgical ability,” Ianchulev concluded.

The article is adapted from Ianchulev’s presentation at the American Academy of Ophthalmology 2021 annual meeting. He is a scientific adviser to Preceyes Inc. Mount Sinai has invested in this technology.

Articles

Utilizing new technology, surgeons can be 20 to 40 times more precise.

The future is now for robot-assisted glaucoma surgery

Knowledge of the optics of the eye is essential in order to have an understanding of biometry, according to Julie Schallhorn, MD, MS, an associate professor of ophthalmology at the University of California San Francisco, who oﬀered some insight on the topic for new ophthalmologists.

“Most of the refraction of light that is entering the eye takes place at the air–tear ﬁlm interface, and there also is slight divergence at the back corneal surface–aqueous interface, after which refraction occurs through the lens. At [that] point the light then converges onto the fovea,” she explained.

It is clear based on this movement of light that what happens at the various surfaces in the eye is important for determining the power of the lens that will be implanted in the eye. The corneal curvature, anterior chamber depth, eﬀective lens position, and axial length must all be considered, Schallhorn pointed out.

“Accurate measurements of the eye are critical to predicting the lens power,” she said.

The ﬁrst-generation formula used to determine lens power was the Sanders-Retzlaﬀ-Kraﬀ, generally referred to as the SRK formula. In this formula, the IOL power is equal to a constant that compensates for all unmeasured factors minus 2.5 times the axial length minus 0.9 times the keratometry.

Schallhorn explained that if there is an error in the measurement of the axial length, there will be a big error in the power of the IOL, resulting in an ampliﬁcation of the error by 2.5 times. Likewise, an error in the keratometry results in an error in the IOL power, as does an error in the A constant.

“Axial length measurements are incredibly important to the obtaining of the correct IOL power,” she said.

With the modern light-based biometers, utilizing Michelson interferometers, look for an interference pattern between the light entering the eye and a reference arm. 

The result is a spectrum of interference insensitive to patient movement; therefore, despite the normal biologic noise that is present, the result is an accurate measurement of what is going on inside the eye. Because of this capability, a light-based biometry system is far superior to ultrasound biometry for predictability and reliability.

Biometry also can evaluate the corneal curvature by evaluating several points on the ocular surface as well as the diﬀerence in the keratometry reading between the 2 principal axes, Schallhorn explained.

Schallhorn also outlined the steps that must be taken to ensure successful measurements. All things considered, it is important to be fastidious about biometry measurement, she said.

She referred to what she considers to be a valuable tool, Warren Hill’s IOLMaster checklist, which is available at 

https://www. doctor-hill.com/physicians/download.htm

. The checklist lays out all the factors involved in obtaining accurate measurements.

In addition, the ocular surface must be considered because of the potential eﬀect on the biometry measurements because of, for example, epithelial basement dystrophy and Salzmann nodular degeneration and the eﬀects before and after treatment.

Topography is important to paint a clear picture of the corneal shape, which ultimately aﬀects the vision, as in patients with keratoconus. Lastly, she advised double-checking the biometry printout for the correctness of every factor for every patient.

“It is important to know how your biometer works, check the cornea carefully, obtain a topography map, be fastidious in your measurements, and double-check your work,” Schallhorn concluded.

This article is adapted from Schallhorn’s presentation at the Real World Ophthalmology meeting. She is a consultant to Carl Zeiss Meditec.

Proper measurement of the eye is key to predicting lens strength.

Biometry 101: Capturing the accurate power

Article reviewed by Karolinne Maia Rocha, MD, PhD

The presbyopia landscape is crowded to­day with innovations to treat this condition, including corneal procedures, pharmacologic treatments, scleral procedures, and phakic and intraocular (IOL) lenses, according to Karolinne Maia Rocha, MD, PhD, director of cornea and refractive surgery at the Medical University of South Carolina in Charleston.

Procedures that are coming down the pike in­clude focal denaturization of collagen fibers that involves use of a femtosecond laser to change the corneal refractive index (laser-induced refractive index change).

Another option is lenticular intrastromal ker­atoplasty, which uses a precut, donor stromal lenticule that is inserted either under a femto­second flap or in a pocket.

Corneal inlays/onlays, presbyopic excimer laser ablation profiles, and modified monovision are also available.

The femtosecond laser pulses may soften the presbyopic crystalline lens and restore accom­modation.

Small aperture optics or the pinhole effect can be achieved by pupil modulation induced pharmacologically. Liquid Vision eye drops (Presbyopia Therapies), CSF-1 ophthalmic solution (Orasis Pharmaceuticals), AGN-190584 (Vuity; Allergan), and FOV Tears (developed by Colombian researcher Felipe Vejarano).

Rocha said she is excited by the prospect of a smaller aperture can improve the depth of focus.

“A pinhole placed in front of the eye can restrict the peripheral vision,” she said. “How­ever, the advantage is that when the pinhole is ‘placed’ at the iris plane, the depth of focus is ex­tended without restricting the peripheral vision.”

The so-called “sweet spot” regarding the size of the natural pupil with constriction may be a range 40% to 50% of the natural pupil size to achieve extended depth of focus without com­promising the distance vision, she said.

Evaluating this approach in the phase 3 GEM­INI 1 clinical trial using AGN-190584 showed that the study patients gained 3 lines of vision 6 hours after drop instillation at day 30. The peak drug effect was at 1 hour after instillation, but the change remained for up to 24 hours.

Other presbyopic approaches include decreasing the lens stiffness and restoring lens elasticity with EV06 (Novartis) and Vision Correction (NanoDrops) causes a change in the refractive index.

The laser scleral microporation (LSMTM) proce­dure is performed in 4 quadrants for less than 8 seconds in each quadrant to uncross-link the scleral myofibrils, thereby restoring the mechan­ical efficiency of the natural accommodative mechanism and improving biomechanical mobility to achieve accommodative power, Rocha said.

Several IOL designs are available to treat pres­byopia at the time of lens surgery, ie, accommo­dative, extended-depth-of-focus, small aperture, and multifocal IOLs.

In addition, another procedure, refractive index shaping, will be able to modify monofocal acrylic IOLs to address presbyopia.

“In the future, we will be able to use the femtosecond laser for refractive index shaping, in which [the] laser is applied to an acrylic IOL that selectively changes the polarity and the refractive index,” Rocha said. “This procedure facilitates creation of 3-dimensional structures within an IOL. This takes an acrylic monofocal IOL to a multifocal IOL and vice versa.”

Rocha said she looks forward to a new level of future patient simulation, whereby patients can actually experience the real world through mul­tifocal correction before IOLs are implanted or contact lenses are fitted to facilitate the optimal correction for them.

This article is adapted from Rocha’s presentation at the virtual Real World Ophthalmology meeting. She is a consultant to J&J Vision, Bausch + Lomb, Allergan, Alcon, OysterPoint, LaserACE, Dompe, and Carl Zeiss Meditec.

The future of this age-related condition is bright and in focus.

Ophthalmology Times: February 2022

The future is now for robot-assisted glaucoma surgery

Biometry 101: Capturing the accurate power

Presbyopia: the newest subspecialty?

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