The effects of Nd:YAG (neodymium: yttrium-aluminum-garnet) laser peripheral iridotomy (PI) on contra-lateral eye anterior chamber parameters of patients with unilateral angle closure. Jayarathna DGAI1 Jayawickrema N1 Masinghe KM1 Amarasinghe B2 1 Registrar, National Eye Hospital, Colombo, Sri Lanka 2 Consultant Ophthalmologist, National Eye Hospital, Colombo, Sri Lanka Introduction The neodymium:yttrium-aluminum-garnet (Nd:YAG) peripheral iridotomy is performed to control intraocular pressure in acute angle closure glaucoma and prophylactically in the contralateral eye to reduce the risk of an event of acute angle closure. The purpose of this study was to assess the immediate effects of Nd:YAG laser peripheral iridotomy on anterior chamber parameters in contralateral eye of the patients presenting with unilateral acute angle closure. Methodology Study population of 14 patients was selected with unilateral acute angle closure glaucoma presented to the out patients department of National Eye Hospital, Sri Lanka, from 1st of January to 31st of July, 2016. Informed written consent was obtained from the patients prior to the procedure of YAG PI in bilateral eyes. Diagnosis of acute angle closure was reached through the below mentioned 1diagnostic criteria. Presence of at least 2 of the following symptoms: Ocular or periocular pain Nausea or vomiting Antecedent history of intermittent blurring of vision with haloes Presenting IOP > 21 mm Hg Presence of at least 3 of the following signs: Conjunctival injection Corneal epithelial edema Mid-dilated unreactive pupil Shallow anterior chamber Pre PI AS OCT Post PI AS OCT Pre procedural anterior chamber parameters were assessed including Anterior Chamber Depth (ACD), Anterior Chamber Area (ACA), Angle Opening Distance at 500 microns (AOD 500). Peripheral iridotomy was performed at supero-temporal iris of the contralateral eye by photo-coagulation with frequency doubled YAG laser for 80% to 90% of depth with beam duration of 10ms, power of 1500mw, spot size of 50 microns. Final 10% to 20% was completed by photo-disruption with single frequency YAG laser. The size of the iridotomy was of average size. One hour after the procedure the above mentioned parameters were reassessed in repeated AS-OCT. Pre and post procedural results were analyzed statistically using the paired t test assuming the data are normally distributed. Results Anterior Chamber Depth (ACD) (mm) Pre & Post PI Anterior Chamber Depth : Graphical representation Pre PI ACD (mm) Post PI ACD (mm) Mean 2.1986 2.2121 Standard Deviation 0.21144 0.19912 Standard Error of Mean 0.05651 0.05322 95% confidence interval = - 0.02307 to - 0.00407 The two-tailed P value = 0.009 (< 0.01)

Conclusion Discussion and Suggestions Anterior Chamber Area (ACA) (mm) Pre & Post PI Anterior Chamber Area : Graphical representation Pre PI ACA (mm) Post PI ACA (mm) Mean 15.5843 16.4479 Standard Deviation 2.43075 2.28395 Standard Error of Mean 0.649645 0.610413 95% confidence interval = - 1.16136 to - 0.56578 The two-tailed P value = 0.000029 (< 0.01 ) Temporal Angle Opening Distance 500 (AOD 500) (μm) Pre & Post PI Temporal AOD 500 : Graphical representation Pre PI ACD (mm) Post PI ACD (mm) Mean 379.85 589.9286 Standard Deviation 157.38 157.33 Standard Error of Mean 42.06 42.04 95% confidence interval = -259.68 to -160.46 The two-tailed P value = 0.000001 (< 0.01) Nasal Angle Opening Distance 500 (AOD 500) (μm) Pre & Post PI Nasal AOD 500 : Graphical representation Pre PI ACD (mm) Post PI ACD (mm) Mean 349.00 508.57 Standard Deviation 101.97 98.71 Standard Error of Mean 27.25 26.38 95% confidence interval = -217.52415 to -101.61 The two-tailed P value = 0.000048 (< 0.01) Conclusion There is a significant increase in the anterior chamber parameters including anterior chamber depth, anterior chamber area and the angle opening distance immediately following Nd:YAG laser PI in contra-lateral eye of patients diagnosed with unilateral angle closure, which is clearly evident and hence could be assessed using AS-OCT. Discussion and Suggestions Nd:YAG laser is a solid-state laser that can disrupt ocular tissues by achieving optical breakdown with a short, high-power pulse. Optical breakdown results in ionization, or plasma formation, in the ocular tissue3. This plasma formation then causes acoustic and shock waves that disrupt tissue. Over the last few decades the Nd:YAG laser has replaced surgical peripheral iridotomy due to practical advantages over the latter. The fellow eye, which usually shares the anatomic predisposition for increased pupillary block, is at high risk for developing acute angle closure in future. An untreated fellow eye has a 40% to 80% risk of developing an acute attack. It is recommended that the contra-lateral eye be treated prophylactically with laser peripheral iridotomy2. Following prophylactic Nd:YAG PI anterior segment parameters statistically significantly increased to a favorable level, yet the clinical significance should be assessed by following up the patient for intraocular pressure rises and possible acute angle closure events despite of undergoing prophylactic PI. Therefore follow up for such consequences, effect of cataract surgery and other treatment modalities are suggested for continued phase of this study. References 1Khondkaryan A, Francis BA 2013, Angle-Closure Glaucoma, https://www.aao.org/munnerlyn-laser-surgery-center/angleclosure-glaucoma-19 2Friedman DS, Who needs an iridotomy?British Journal of Ophthalmology 2001;85:1019-1021. 3Steinert RF 2013, Nd:YAG Laser Posterior Capsulotomy, https://www.aao.org/munnerlyn-laser-surgery-center/ndyag-laser-posterior-capsulotomy-3