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Glaucoma Lasers in Open Angle Glaucoma Jason Cheng, MBBS, BSc, FRCOphth, FEBO 1 and Yvonne M Buys MD, FRCSC 2 1. Associate Consultant, Department of Ophthalmology and Visual Science, Alexandra Health, Khoo Teck Puat Hospital, Singapore; 2. Professor, Co-Director, Glaucoma Unit, Department of Ophthalmology and Vision Sciences, University Health Network, University of Toronto, Toronto, Canada Abstract Lasers have been used in open angle glaucoma for more than 40 years and have grown in importance in recent years. This article reviews the latest research and trends in the use of lasers in the management of open angle glaucoma. Keywords Glaucoma, laser, review, trabeculoplasty, POAG, ALT, SLT, cyclophotocoagulation Disclosure: The authors have no conflicts of interest to declare. Received: January 20, 2014 Accepted: March 13, 2014 Citation: US Ophthalmic Review, 2014;7(1):50–3 Correspondence: Jason Cheng, MBBS, BSc, FRCOphth, FEBO, Alexandra Health, Khoo Teck Puat Hospital, 90 Yishun Central, 728828, Singapore. E: Lasers have been used in ophthalmology since within a decade of its invention in 1960. The argon laser was found to be most suitable for the eye as the blue-green wavelengths were better absorbed by hemoglobin and melanin in ocular tissue. The first reported use of lasers for glaucoma was in the 1970s, initially for iridotomy and trabeculoplasty. The physician now has a range of lasers to use for the prevention, modulation, and treatment of glaucoma and to augment surgical procedures. This article reviews the types of lasers used in open angle glaucoma, their efficacy, and side effects. Laser to the Trabecular Meshwork Laser Trabeculoplasty (Argon Laser Trabeculoplasty and Selective Laser Trabeculoplasty) Indications Open angle glaucoma as primary treatment or as an adjunct to medical therapy. Efficacy The glaucoma laser trial 1 showed that argon laser trabeculoplasty (ALT) was at least as effective as initial treatment with timolol maleate 0.5 % and the procedure gained popularity in the 1990s. However, the visible thermal damage, limited repeatability, late pressure rise, and treatment failure along with the technical skill required to correctly identify angle structures likely reduced its popularity among comprehensive ophthalmologists. A laser that delivers over 100 times less energy than ALT while providing a similar intraocular pressure (IOP)-lowering effect was developed by Latina 2 in 1995. It is a frequency-doubled, Q-switched, neodymium: yttrium aluminium garnet (Nd:YAG) laser and delivers a 400 µm diameter treatment spot in 3 nanoseconds. In addition, the large spot size facilitating less- precise identification of angle structures during laser application led to increased interest in this modality. 3,4 Table 1 highlights the differences in the characteristics of ALT and selective laser trabeculoplasty (SLT). 50 SLT does not cause visible thermal damage to the trabecular meshwork and its surrounding tissues and the low power and short duration of this laser is thought to selectively target the pigmented trabecular meshwork cells. SLT has been shown to be repeatable 5 and has theoretical promise to have greater repeatability than ALT, although this has not been convincingly proven. 6 Two independent meta-analyses in 2013 reported on six randomized controlled trials (although not the same six) comparing SLT with ALT. Wang and He reported no significant difference in IOP lowering at all-time points up to 5 years in patients who were naïve to laser, and no statistical difference in IOP lowering at 6 months for those who had previous laser treatments. 7 By contrast, Wang and Cheng reported an overall weighted mean difference of 0.6 although they did not stratify the time to follow up. 8 For repeated treatments, Wang and Cheng reported SLT to be more effective than ALT with a weighted mean difference of 1.48. Technique Pretreatment with topical anesthetic and prophylactic hypotensive agent such as apraclonidine or brimonidine. Various lenses may be used for ALT including the Goldmann three mirror lens, the Ritch trabeculoplasty lens, and the LASAG contact glass anterior (CGA) lens. The Latina lens was designed specifically for the SLT and has no spot size magnification. The laser settings are shown in Table 1. The ALT aiming beam is focused on the junction of the anterior non-pigmented and posterior pigmented trabecular meshwork with the power titrated to achieve slight blanching. For SLT, the spot size is fixed at 400 µm and power is titrated to achieve © TOU C H M E D ICA L ME D IA 2014