Reply to Athanasiadis et al

Abstract

Sir, We are grateful to Dr Athanasiadis et al1 for their interest in our manuscript,2 and for this opportunity to reiterate the points made therein. Zonular disruption during laser peripheral iridotomy (LPI) can occur if sufficient energy is applied or if there is pre-existing zonular weakness. Indeed, Nd:YAG laser zonulotomy and hyaloidotomy are used in the management of some cases of aqueous misdirection syndrome. However, in our experience from the specialist angle-closure clinic at Moorfields City Road, the Zhongshan Angle-closure Prophylaxis (ZAP) study in Guangzhou, China (ISRCTN45213099), and our research programme in Mongolia, culminating in over 4500 LPIs and 800 phacoemulsification procedures in the same pool of patients, we have not encountered this problem with LPI. Dr Athanasiadis's case report3 omits to mention where the initial phaco wound was (ie superior or temporal). This may have some bearing on the location of the dehiscence. The report also does not mention the power and number of shots during LPI. We were puzzled as to why two iridotomies were performed in each eye of the patient reported in this case. One adequately sized iridotomy is sufficient in management of angle closure. Angle closure is known to affect people with a variety of genetic mutations that cause zonular abnormalities and weakness as part of their phenotype: PXF, FBN1 (Marfan and Weill Marchesani syndromes), lysyl hydroxylase (Ehler Danlos VI), MTHFR (homocystinuria), and ADAMTS4 and ADAMTS10 (spherophakia). As per the principles of Occam's razor, we would suggest that the case Dr Athanasiadis et al report had a pre-existing zonular weakness and/or received higher-than-usual amounts of laser energy. It is important to emphasise that LPI should be performed by a skilled, experienced operator, using the lowest possible power to achieve a satisfactory iridotomy. We would advocate the use of sequential argon/YAG iridotomy in patients with thick, dark brown irides.4 Regarding the risk of cataract formation/progression after PI, similar principles to those outlined above apply. With excess power or inappropriately applied laser treatment, it is possible to induce lens opacities, but this can be avoided with careful and precise treatment. Studies suggesting that LPI accelerates the formation of age-related cataract are exclusively retrospective studies, or individual case reports. Some have used surrogate outcome measures, such as reduction in visual acuity, rather than lens opacity grading. We believe that our study,2 which was carried out prospectively, in the largest number of treated cases so far studied, with a control group selected from the community, using a standardized objective assessment of lens opacity (LOCS III system), currently constitutes the most robust scientific assessment of the risk of lens opacity after laser iridotomy. The choice of either laser iridotomy or lens extraction for management of angle-closure glaucoma should be informed by the ongoing MRC EAGLE trial (https://viis.abdn.ac.uk/HSRU/eagle/). We are grateful to the journal for giving us the opportunity to reiterate these points.