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Aiming true: optimising enVista toric outcomes (video included)

 

With Bausch + Lomb releasing the toric version of its enhanced enVista platform, surgeons discuss how they are improving outcomes, even in complex cases. The company is also incorporating a new generation toric formula into its lens calculator.

In October 2020, ophthalmic device manufacturer Bausch + Lomb (B+L) released its upgraded enVista monofocal intraocular lens (IOL) in Australia, featuring a modified lens material for faster unfolding and a new pre-loaded delivery system.

These enhanced features were welcomed by ophthalmologists who have traditionally relied on the hydrophobic acrylic lens – first launched in 2012 – for its robust, glistening-free material, visual clarity, predictable outcomes and, more recently, unexpected functional intermediate vision in some patients reported by some surgeons.

Since the arrival of the improved enVista monofocal with the new SimplifEYE delivery system, B+L has introduced the toric form of the lens (called the enVista Toric pre-loaded). Now, surgeons report the lens’ other attributes – such as aberration-free optics, haptic design and rotational stability – are contributing to optimal outcomes for astigmatic patients and others with irregular corneas.

Download a short video of Dr Sunil Warrier performing an enVista Toric procedure here (1.30 min duration, 40MB).

In recent months, B+L has also been updating its enVista toric calculator to now incorporate the Emmetropia Verifying Optical (EVO) Formula 2.0. It’s a new generation formula developed by Singapore’s Dr Tun Kuan Yeo who completed his 2015 anterior segment fellowship under internationally renowned Western Australian ophthalmologist and creator of the Barrett Formula Suite, Professor Graham Barrett.

Dr Audrey Talley Rostov.

Seattle-based corneal, refractive and cataract surgeon Dr Audrey Talley Rostov spoke of her experience with the new enVista Toric pre-loaded at last year’s Australian Society of Cataract and Refractive Surgeons (AUSCRS) conference, presenting on aberration neutral IOLs in complex cataract cases such as post-refractive surgery, keratoconus, transplant patients and other irregular corneas.

She says complex cases make up about 30% of her cataract work, with the enVista Toric pre-loaded being a mainstay due to its versatility.

B+L has designed the IOL with step-vaulted, modified-C haptics that vault the haptic posteriorly to form direct contact with the capsular bag. The haptics also include fenestration holes that help evenly disperse post-operative capsular contractile forces.

Talley Rostov says these attributes result in a very stable IOL, with little concern about rotation.

“Which we know is very important when considering IOL toric alignment, and the ability of the IOL to stay precisely where you place it,” she says.

“And we know hydrophobic acrylic IOLs opposed to hydrophilic are also very stable, and when you’re talking about cases of DMEK, DSEK or a retinal procedure where there maybe air and gas in the eye, a hydrophilic lens may opacify, but with the enVista platform you don’t have to worry, so it’s versatile and amenable to those situations.”

With complex corneal cases making up a significant proportion of her work, Talley Rostov says the aberration-free lens design has been key to providing optimal outcomes for patients who may have decentration from previous refractive surgery, zonular issues, corneal transplant, high angle kappa, or differences in the alpha angle. She has also found the design ideal for multifocal or aberrated corneas such as keratoconus.

“While some IOLs are excellent, they have additional negative spherical aberration and this creates issues in cases that could involve some decentration,” she explains.

“If you’re using a platform with no additional spherical aberration (enVista), you’re going to get the same great outcome, even if there’s some difference between the visual axis and centre of your IOL. That makes it extremely versatile, user-friendly for the surgeon, as well as giving great outcomes for your patients.

“I use the enVista Toric routinely with patients after corneal transplantation. As good as you might be, there usually is some residual astigmatism – and just because they have previous corneal pathology, there’s no reason to believe they are stuck with less-than-ideal vision; we have a real opportunity to make a big difference with the enVista platform.”

The enVista Toric pre-loaded.

In other complex cases, Talley Rostov has implanted the enVista Toric pre-loaded in a patient in his 50s with a history of congenital lens coloboma where a portion of the natural lens is missing. He also had -3.0 D of astigmatism. Performing femtosecond-laser-assisted cataract surgery (FLACS), she combined the enVista Toric with a capsular tension ring and found the lens was well-centred.

“Even if there is decentration over time, I don’t have to worry about him developing a less-than-perfect result due to the aberration-free design. He had a fantastic refractive outcome; he said he’d never had better vision in his life.”

Another case involved a 64-year-old woman who had cataract surgery elsewhere with a toric multifocal IOL. She was unhappy with her vision, even with a corrected residual refractive error. Tomography revealed previously undetected keratoconus with expected increased higher order aberrations. An IOL exchange was performed, with the enVista Toric ultimately implanted. There was also a radial keratotomy (RK) patient she treated with the enVista.

“Both had excellent outcomes. The keratoconus patient, in particular, had a huge improvement in quality of vision, could drive again and her glare, haloes and other aberrations were resolved.

“With RK, once a refractive patient, always a refractive patient – and when it comes to cataract surgery they are seeking that crisp vision just like when they had RK, LASIK or PRK surgery, so the ability to correct astigmatism for these patients means you’re doing them a great service.”

Talley Rostov has also found the IOL’s fenestration holes allow for intraoperative lens manipulation. For example, she’s been able to rotate the IOL in either direction once implanted (some can only be dialled in one direction), if the lens becomes slightly off axis during steps like viscoelastic removal.

‘Surprising’ intermediate vision

Queensland ophthalmologist Dr Sunil Warrier practises at Terrace Eye Centre and Redlands Eye Specialists in Brisbane and is head of the ophthalmology department at the Mater hospital network. He has been among the first Australian specialists to offer the enhanced enVista platform.

Dr Sunil Warrier.

About 65% of his cataract patients receive a monofocal, with the enVista being his primary choice, and the enVista Toric pre-loaded accounting for around 30% of that. With B+L changing the ratios of two polymers in the lens material, Warrier has noticed drastic improvements with the faster unfolding time, and overall ease-of-use with the SimplifEYE preloaded delivery system.

“With pre-loaded IOL systems, the two common methods involve either screwing it down, or a plunger mechanism; this screw system (SimplifEYE) is very controlled so you can stop at any point,” he says.

“Ninety-eight percent of the time you can have the lens unfold in the bag, so there’s no need to take a second instrument and push it in, effectively cutting out an additional step.”

Like Talley Rostov, Warrier has been impressed with the enVista’s rotational stability, which he puts down to how the haptics interact with the capsular bag. He’s also found an unexpected number of patients achieving intermediate vision.

This surprising advantage is to do with pre-existing corneal spherical aberration, as discovered by Californian ophthalmologist Dr Mitchell Shultz. Through corneal analysis, he’s found patients in the +0.25 to +0.31 μm positive corneal spherical aberration range get the most enhanced depth-of-field.

Warrier spoke to Shultz about this, and then asked his clinic’s optometrist to measure intermediate vision in enVista patients.

“Over 50% were 6/12 or better at 80-100cm, and some were even 6/6,” he explains. “This has surprised me because it’s not really the aim of this lens. Patients still need reading glasses, but that’s not really the sales pitch for this. When they’re driving, they can see the dashboard comfortably, and the distance is great.”

New generation formula 

For surgeons to optimise outcomes, B+L realised it needed to modernise its toric calculator. Over time, use of its legacy calculator has diminished in Australia, largely because it only accounted for anterior corneal astigmatism.

Australian surgeons have increasingly turned to later generation formulas such as Barrett Toric Calculator (BTC) and EVO Toric 2.0 that account for newer parameters such as posterior corneal astigmatism – influential in toric refractive outcomes.

Dr Tun Kuan Yeo.

The first generation of the EVO formulas were released by Dr Tun Kuan Yeo in 2017. The results of clinical studies showing its equivalence and/or superiority to other leading formulas prompted B+L to embed the EVO Toric Formula 2.0 in its enVista Toric calculator.

Yeo, a senior consultant with the National Healthcare Group Eye Institute at Tan Tock Seng Hospital, Singapore, and senior clinical lecturer for Yong Loo Lin School of Medicine, National University Singapore, says his 2015 fellowship under Prof Barrett was influential in him developing the formula.

At the time, he was conducting toric calculation research, with the BTC “exploding” in popularity that year. In his free time, he was conducting research on posterior corneal astigmatism and stumbled across an algorithm that could predict for this and be applied to any standard formula.

“But because of the shortcomings of the traditional standard formulas, I decided to create my own formula so it could bring the best out of the algorithm,” he explains.

In a presentation in 2019 at the American Society of Cataract and Refractive Surgeons Meeting, which won best paper of the session, Yeo presented a comparison of the performance of different toric formulas in 117 eyes.

He says it showed the EVO Toric had the highest percentage of eyes within 0.50D prediction for cylinder, effectively equivalent to the BTC, and preforming better than the Abulafia-Koch regression, Johnson and Johnson Vision online toric calculator, and Holladay I toric formula.

According to Yeo, for IOL power calculations, traditional formulas haven’t performed well in extreme eyes, a shortcoming his EVO formula has also sought to address.

They didn’t account for newer parameters like anterior chamber depth, lens thickness or central corneal thickness that either couldn’t be measured as accurately, or at all, during their time.

“The older formulas use less measurement parameters that are not able to address some of the outliers,” he says.

“For example, traditional formulas were built based on ultrasound axial length, but newer measurements of optical biometry are more precise, and the newer formulas such as the EVO harness these newer measurements and are able to correct for the bias seen in extreme eyes. At the same time, the theory behind the formula seems to fit a lot of different eyes, and that is why we are seeing improved accuracy today.”

Yeo made his formula freely available online to the public in 2017. His efforts have also seen him invited to the exclusive IOL Power Club. Today, Google Analytics figures show an average of 900 EVO IOL calculations are performed daily worldwide, with Spain ranking first and Australia – where the Barrett formulas remain popular – ninth.

The EVO formulas are based on the theory of emmetropization and generate an ‘emmetropia factor’ for each eye. Yeo has already developed a third version, which is in the process of being validated.

“It is mainly to improve accuracy in extreme eyes: very short eyes, long eyes, flat keratometry, steep keratometry, and other atypical eyes because we are doing very well for the average eye,” he says.

“Because technology improves, the formula is designed in a way it can be upgraded, scalable and futureproof, so that if new measurements are available, they can be incorporated easily.”

Finally, with the introduction of the EVO Toric 2.0 formula, Yeo says B+L will become one of the few IOL manufacturers to use an online toric calculator that will not only predict the toric power, but also the IOL power.

More reading

Rethinking what’s possible with the enVista IOL

Eyecare spin-off Bausch + Lomb files for IPO

In pursuit of more precise vitrectomy

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