How Head, Eye Movements Affect Cataract Surgery

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Outcomes of modern cataract surgery are overwhelmingly excellent. But ophthalmologists are always in search of ways to tweak their proto­cols to further reduce the incidence of intraoperative complications and subsequent suboptimal results.

A Scottish group set out to investi­gate a long-posed, but little researched, question: Would limiting head motion during cataract surgery be beneficial to surgical outcomes?

“We realized that without measuring head drift we are unable to quantify how effective head stabilization tech­niques are and whether they should be used in clinical practice,” said coauthor Kerr Brogan, MbCHB, of the Tennent Institute of Ophthalmology at Gart­navel General Hospital, in Glasgow, Scotland. He also noted that “head stabilization is a controversial issue, as some may see taping the head as a form of restraint.”

Low- and high-tech tools. In developing the study, the team employed a creative combination of lower-tech tools and a virtual reality device.¹ “The absence of availability of eye tracking technology to accurately measure intra­operative eye movements inspired us to produce our own objective method for measuring head drift during cataract surgery. We also decided to subjectively simulate eye movements on the cataract surgical simulator while trainee oph­thalmologists performed the capsulor­rhexis exercise,” Dr. Brogan said.

Measuring head drift. The first stage of the 2-pronged study was intended to establish baseline measurement of head drift during real-life cataract surgeries (N = 12) by experienced ophthalmolo­gists. In each case, the researchers took a photo of the patient’s eye with the speculum in place and rulers alongside it. These images were cropped and edited to only contain the rulers, then superimposed over the original video prior to playback. The speculum was used as a fixed point and correlated with the superimposed virtual rulers to measure maximum head drift in each direction throughout the operations.

Measuring eye movements. In the second stage, the researchers attached string to the “eye” of the Eyesi surgery simulator (VRmagic). This enabled them to pull the eye back and forth laterally and medially, in 5-mm incre­ments every 3 seconds, as 6 trainees performed the capsulorrhexis portion of simulated surgeries.

Results. The first phase measured the maximal mean head drift during surgery as 3.1 mm medially (range, 2-7 mm); 2.9 mm laterally (range, 2-4 mm); 2.6 mm superiorly (range, 1-5 mm); and 1.9 mm inferiorly (range, 1-4 mm).

“We found head drift to be greatest medially, with the maximum movement being 7 mm. This caused pooling of fluid at the medial canthus, resulting in a submerged corneal surface and poor view due to light reflections,” Dr. Brogan said. “Eleven of our 12 cases ultimately had to have repositioning of the microscope or the patient’s head during surgery to compensate for this head drift and to regain an optimal surgical view.”

In the study’s second phase, the introduction of eye movements caused a statistically significant deterioration in the trainees’ performance, as judged by the Eyesi’s software on a 100-point scale. Their mean baseline score on the overall task fell from 92.7 ± 4.3 to 76.9 ± 10.3. Their score on “roundness of the capsulorrhexis” fell from 89.4 at baseline to 57.5.

Next step. Dr. Brogan said his group hopes that the study’s methods can be replicated by others, to prepare junior cataract surgeons for the challenge of intraoperative eye movement as well as to help determine the value of head stabilization during cataract surgery.

—Linda Roach

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1 Brogan K et al. Eye (Lond). Published online Feb. 21, 2018.

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Relevant financial disclosures—Dr. Brogan: None.

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