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May 10, 2016

Learn how curiosity propels astigmatism innovations

Perhaps none so much as Graham D. Barrett, MD, a “pre-eminent expert in cataract and refractive surgery, and corneal and anterior segment disorders and surgery,” who was chosen to deliver the 2016 Charles D. Kelman Innovator Lecture at this year’s American Society of Cataract and Refractive Surgery meeting.

New Orleans-Using cataract surgery as a means of reducing astigmatism has fascinated many.

“Perhaps no other innovation has dramatically changed ophthalmology the way Dr. Kelman did when he introduced phaco in 1967,” said Prof. Barrett, clinical professor, University of Western Australia, and consultant ophthalmic surgeon at the Lions Eye Institute as well as Sir Charles Gairdner Hospital. “It was a wonderful example of creativity.”

Creativity underlies innovation, and at the core of innovation is a natural curiosity, inspiration, and persistence, Prof. Barrett said.

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“I’ve been curious about a lot of things, but since the beginning, it’s been astigmatism,” he said, adding he first became intrigued by the phenomenon in his earliest days as a resident.

“I was intrigued by the concept of intraoperative keratometry, and thought a semi-quantitative device would be helpful,” he told attendees. So he made one. And 35 years later, he stumbled upon it in a kitchen cupboard “and found it still works.”

Imaging as data source

Imaging the eye and using that data to better understand astigmatism was another innovation.

Prof. Barrett found taking an original image and superimposing a rotated image would allow the observer to look down and see the amount of astigmatism a patient had.

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“It would give you the axis of astigmatism and the magnitude of the astigmatism,” he said.

Using an enhanced keratometer, “by aligning the handle and selecting the most circular image, you can quantify the amount of astigmatism,” he said, and he began to use these routinely on his patients.

But what was still unclear after all the discussions about measurement and what they meant was how to actually correct this astigmatism during the time of surgery.

“I wanted to know what the impact of the incision was on the astigmatism and how that factored into toric IOL alignment,” he said.

Axis varies, centroid value does not

What he found was that the axis varies widely, but the centroid value does not.

“It doesn’t matter where you put the incision-temporal axis or steep axis. The centroid value is pretty much 0.1 or less,” he said. “Even with smaller incision sizes, it’s irrelevant where you place the incision, the centroid value remains around 0.1. I confirmed this with a series of more than 1,000 eyes.”

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In a personal series of 40 eyes with smaller incisions of 2.2 to 2.4 mm, centroid values do not change.

His advice: “Don’t operate on the steep axis to reduce astigmatism, as it’s too variable. Preferably go on the temporal axis and go to 2.4-mm incision and use a centroid value of about 0.1, regardless of the prediction.

Despite accurate keratometry, he said, implantation is not always predictable.

Toric IOL more challenging choice

“Choosing the correct toric IOL for patients is more challenging than choosing a spherical IOL power,” he said.

Toric IOL alignment is a critical component to its success, and Robert H. Osher, MD, “first convinced me freestyle marking was not enough,” Prof. Barrett said.

Instead, Dr. Osher’s concept of “iris fingerprinting” provides more reliable results, and it’s now being incorporated into image-guided systems.

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Prof. Barrett has developed the “ToriCam” app to aid in axis marking, where “all you need is the app and a felt-tip marking pen,” he said.

First, dry the limbus and mark where the 180° axis is, he said. “It doesn’t matter if you’re not spot on. Use the app to align with the mark and you’ll have the previous five images the app took-allowing you to see where the true axis is.”

In an analysis of 40 eyes comparing slit lamp and freehand alone to both slit lamp and freehand with the ToriCam showed the combination improved accuracy by 50% in the slit lamp combination and by 68% in the freehand combination.

Javal's rule

Javal’s rule

Louis Ãmile Javal, MD, a 19th-century ophthalmologist, first noted that he could not account for total ocular astigmatism by simply measuring the power of the anterior cornea. Known as Javal’s rule, he postulated the posterior cornea contributed about 0.5 D of against-the-rule astigmatism.

“When we refract a patients, the ocular astigmatism does not always reflect the corneal astigmatism,” he said.

It was not until Douglas D. Koch, MD, reminded people a few years ago of the importance of the posterior cornea in toric IOL calculations during his own Innovator’s Lecture that Javal’s rule began to be understood.

“If you ignore the posterior cornea, you’ll end up with about a 0.3 D overcorrection for patients with against-the-rule astigmatism and about 0.5 D overcorrection for those with with-the-rule astigmatism,” Prof. Barrett said. “You need to measure where the lens is sitting, and not where you think it’s sitting.”

In a study of his own patients (n = 160) using the Holladay formula, Prof. Barrett found 28.8% were within 0.5 D of residual astigmatism. Using the Barrett formula, which included effective lens position and considers lens position for each individual patient versus what is known about the average eye, provided a better outcome, but not a “great” one, he said.

“Nomograms are improving, but none are as accurate as an online calculator,” he said, adding his own True-K toric IOL calculator is now available online.

Clinicians know from several large cohort studies that about 80% of patients have more than 0.5 D of astigmatism, and that 0.75 D of astigmatism has more of an impact on vision than 0.75 D of spherical error.

“Some studies suggest that less than 0.5 D of astigmatism is really minor,” he said, who disagrees.

He recommends using toric IOLs for even low levels of astigmatism, and has been able to get 86% of his patients with with-the-rule astigmatism and 83% of his patients with against-the-rule astigmatism to within 0.5 D.

“Target a minimum residual cylinder in all your patients,” he said.

Where innovation starts

Prof. Barrett carries with him an article he once read in The New York Times where Isaac Asimov (“a personal hero of mine”) was asked by the U.S. government to encourage innovation. He politely declined to do so.

Instead, he wrote about creativity and that he thought creativity cannot be encouraged, but must come from an inward reflection.

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For Prof. Barrett, he believes a sense of curiosity drives the innovation process. He “sees it daily” in his grandchildren, and he thanked his parents for providing him the ability to maintain that sense of curiosity as an adult.

“Inspiration is not only internal, but stimulated by friends and colleagues,” he said, citing one mentor of his who told him never to limit his own horizons.

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“Finally, what has allowed me to remain persistent is my wife, Ann, who often put aside her own pursuits to support mine,” he said, getting emotional. “I am truly humbled by this honor.”

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