Home News P1, P4 Purkinje reflections offer reliable intraoperative patient fixation method

P1, P4 Purkinje reflections offer reliable intraoperative patient fixation method



Thompson reports being a consultant and researcher for and equity owner in Centricity Vision.

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P1 and P4 Purkinje light reflections can be recreated intraoperatively if patient fixation is hindered and may assist in capsulotomy centration during cataract surgery, according to a study.

“When the patient fixates properly, and they’re looking at the microscope light that is coaxial with the surgeon and the surgeon wants to center surgery on their visual axis, Purkinje 1 and Purkinje 4 have a very distinct and reproducible relationship,” study author Vance Thompson, MD, told Healio/OSN. “If the patient is moving their eye because they’re confused or under anesthesia, the surgeon can simply manually reapproximate these images and rotate the eye to where P1 and P4 have the same exact relationship as they did when the patient hadn’t had anesthesia yet and were reliably fixating. Whether doing a manual capsulotomy or an automated capsulotomy like Zepto, this technique can work well.”

Vance Thompson

Vance Thompson

Thompson and colleagues based their research on the concept of subject-fixated coaxially sighted corneal light reflex (SFCSCLR), which depends on patient fixation and a coaxial light source to find a consistent and reproducible marker in the patient’s visual system.

The authors wrote that when patients fixate, they have a “closely spaced and invariant relationship between P1 and P4 that reflects the relationship between their SFCSCLR and P4.” This can be reproduced manually intraoperatively when observing a patient’s fixated eye through a microscope.

“All fixation trials prior to anesthesia end up at the same fixation point and thus show the same P1 and P4 relationship,” Thompson and colleagues wrote. “The unique part of this contribution is this reproducible and very accurate relationship between P1 and P4 and this idea of having something to fall back on if the patient can’t reliably fixate,” Thompson said. “With the knowledge of how helpful P1 and P4’s consistent fixational relationship is I can reproduce that relationship manually and center my implant and my capsulotomy every time.”

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