What is best laser for glaucoma?

Is there still a role for diode lasers, or should micropulse lasers take their place?

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Due to its high absorption by melanin in the target tissues of the ciliary bodies, diode 810nm lasers made transscleral cyclophotocoagulation (TSCPC) less destructive than earlier lasers for treating glaucoma. Now micropulse laser technology may improve safety even more. Still, there may yet be a role for traditional diode lasers, according to presenters at the American Society for Cataract and Refractive Surgeons Glaucoma Day 2018 in Washington DC, USA. Arguing for continued use of diode lasers, Jeffrey Kammer MD, of Vanderbilt Eye Institute, Nashville, Tennessee, USA, noted that the technology reliably reduces IOP and has a safety profile comparable to the gold standard procedures trabeculectomy and tube shunts. He said that concerns over drastic complications, especially phthisis, are overstated. NO PHTHISIS Dr Kammer referenced a prospective study involving 66 patients with neovascular glaucoma comparing diode TSCPC with the Ahmed shunt. Mean IOP was reduced 57% in the diode group compared with 48% in the shunt group. No phthisis cases occurred in the diode group and two in the shunt group (Yildirim, J Glaucoma, 2009). “Even in the worst of the worst glaucoma, phthisis was not an issue,” Dr Kammer said. Other studies have shown diode TSCPC is safe in eyes with good vision, defined as 20/60 or better (Rotchford AP et al. Br J Ophthalmol 2010.), and even as a primary treatment, achieving visual acuity and IOP-lowering results comparable to medications in a contralateral eye study (Egbert PE et al. Arch Ophthalmol 2001). Robert Noecker MD of Yale University and Quinnipiac University responded that micropulse laser technology is a better alternative because it is less likely to burn tissue. “Diode might be okay for end-stage cases, but generally we want to ‘first do no harm’.” REDUCING HEAT BUILD-UP Micropulse lasers reduce IOP as much as diode lasers, with better success after 18 months, Dr Noecker said (Tan A et al. Clin Experiment Ophthalmol 2010;38(3):266-72). And rather than using a continuous burst of energy as does a traditional diode laser, micropulse technology pulses the laser, reducing heat build-up. According to a study at the National University Hospital in Singapore, diode laser tip temperature exceeds 550 degrees C, whereas micropulse laser tips peak at 35 degrees C. This can cause burns, which lead to coagulative necrosis, which continues to progress indefinitely. The result is unstable IOP reduction, hypotony and even phthisis – which does happen, Dr Noecker said. “You don’t want something you can’t reverse from overtreatment, and that is really the true problem with traditional transscleral.” Robert Noecker: noeckerrj@gmail.com Jeffery Kammer: jeffrey.kammer@vanderbilt.edu
Tags: lasers, ASCRS 2018