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Consider factors such as glaucoma severity, eye pigmentation, and medication use when selecting power settings for the MicroPulse P3 device.
Take-home message: Consider factors such as glaucoma severity, eye pigmentation, and medication use when selecting power settings for the MicroPulse P3 device.
By Vanessa Caceres; Reviewed by Nathan Radcliffe, MD
Though technology (MicroPulse P3 Glaucoma Device, Iridex) allows surgeons to personalize glaucoma therapy and reduce IOP, there are ways to work the laser effectively depending on several patient factors, said Nathan Radcliffe, MD.
The MicroPulse P3 is used in conjunction with the CYCLO G6 Glaucoma Laser System in the office or the operating room. This cyclophotocoagulation device controls thermal elevation by chopping a continuous-wave beam into repetitive microsecond pulses (micropulses), which allow the tissue to cool between pulses, Dr. Radcliffe said.
The treatment is efficient, non-incisional, repeatable, titratable, and can help address common concerns about medication compliance.
“The laser itself is powerful enough to cause side effects and risks and powerful enough to induce profound IOP lowering,” said Dr. Radcliffe, glaucoma surgeon, New York Eye Surgery Center, New York. “That’s where personalizing and appropriately titrating it comes into play.”
With use of the MicroPulse, the mean IOP reduced from 38.1 mm Hg to 23.2 mm Hg in a study reported at the American Glaucoma Society meeting in 2015 from Marlene Moster, MD, Philadelphia, according to Dr. Radcliffe. That same study found that the mean number of medications used dropped from 2.54 to 1.77.
A 2014 study reported a 45% reduction in IOP with use of the P3 and a 75% success rate at 12 months, with no cases of hypotony.1
With the 200 cases that Dr. Radcliffe has treated, there has been a 30% to 80% reduction in IOP with no cystoid macular edema or phthisis. There has been one case of worsening cataract. Postoperative inflammation can occur and mydriatic pupil has also been reported.
Dr. Radcliffe follows several pearls to maximize use of the laser for effective results:
· Titrate according to glaucoma severity. For example, if Dr. Radcliffe sees a glaucoma patient with 20/20 vision who is on one or two glaucoma drops, he’ll treat with 2,000 mW delivered for 100 seconds-50 seconds to the top half of the eye and 50 seconds to the bottom half (sparing the neurovascular bundles at 3:00 and 9:00). “You get a 30% pressure reduction and a very good safety profile,” he says.
However, if it’s a patient using four or five eye drops and who has had failed surgeries and 20/200 visual acuity, he’ll likely increase the MicroPulse’s power setting. The strongest setting Dr. Radcliffe uses is 2,500 mW, so he may select that power setting in such a patient and deliver the energy for the same amount of time.
· Consider eye pigmentation. As the laser is better absorbed in eyes with a lot of pigment, Dr. Radcliffe will use a lower setting, at least for starters, in eyes that are dark brown. In a patient with very blue eyes, he may use 2,200 mW for the initial treatment depending on other patient factors. Assess the patient’s willingness to undergo a repeat procedure and treat conservatively until you understand the laser–pigment interaction.
· Go aggressive to reduce medication use. If a patient uses three or four medications, including oral Diamox, Dr. Radcliffe is more likely to start them at 2250 or 2500 mW. “There’s more room to go down in terms of IOP,” he said. “If a patient is on four medications, the likelihood of overtreating and inducing hypotony is low. We can be more aggressive with laser power in eyes that have worse visual acuity,” he said. In contrast, if a patient does not use any medications and has MicroPulse treatment, we would be more cautious with laser settings, typically starting with a power of 2,000 mW. For patients with an IOP of 55 mm Hg or 60 mm Hg, Dr. Radcliffe may treat in the 2,300 or 2,500 mW range and be able to lower their IOP to the mid-teens.
1. Aquino MC, Barton K, Tan AM, et al. Micropulse versus continuous wave trans-scleral diode cyclophotocoagulation in refractory glaucoma: A randomised exploratory study. Clin Exp Ophthalmol. 2015;43:40-46.
Nathan Radcliffe, MD
This article was adapted from Dr. Radcliffe’s presentation at the 2016 meeting of the American Academy of Ophthalmology meeting. Dr. Radcliffe is a consultant for Iridex and other ophthalmic companies.