The burden of PACG

Although primary open-angle glaucoma (POAG) affects nearly three times more people worldwide compared with primary angle-closure glaucoma (PACG), PACG accounts for half of the total cases of glaucoma-related blindness. Those statistics about the burden of PACG underscore the importance of understanding that it resides at the far end of a progressive disease spectrum, and of identifying and taking care of patients at an earlier stage, according to John Thygesen MD, who delivered the keynote lecture, ‘Angle-closure: from suspicion to certainty’, at ESCRS Glaucoma Day 2016 in Copenhagen, Denmark. He reviewed information on the epidemiology of angle-closure, its clinical features, classification, mechanisms, screening, diagnosis, and treatment, but began his lecture with two key messages. “First, POAG is a diagnosis of exclusion. That means gonioscopy must be done to exclude chronic angle-closure,” said Dr Thygesen, Clinical Associate Professor of Ophthalmology and Director of Glaucoma Services, Copenhagen University Hospital, Copenhagen, Denmark. “Second, most cases of angle-closure are asymptomatic. Therefore, blindness develops in the setting of chronic angle-closure.” DETECTION AND TREATMENT According to a consensus statement from the Global Glaucoma Network, evaluation of limbal anterior chamber depth may be an appropriate screening test for angle-closure. Gonioscopy, however, is essential for diagnosis and treatment. Dr Thygesen emphasised that the examination should be performed in a nearly dark room and using both a Goldmann lens and an indentation lens. Treatment decisions for eyes with PAC/PACG should be based on classification using the newer classification system from the International Society for Geographical and Epidemiological Ophthalmology (ISGEO). Unlike the previously used system that was symptom-based, the ISGEO system describes the natural history, staging, tissue damage affecting visual function, and mechanisms for angle-closure, Dr Thygesen said. He encouraged clinicians to follow the European Glaucoma Society Guidelines flowchart for treatment, and he reviewed the indications, effectiveness and drawbacks of the various surgical treatment options for PAC/PACG, citing the consensus statement. Iridotomy or iridectomy is the preferred initial treatment for PAC and PACG. Argon laser peripheral iridoplasty is indicated in eyes with plateau iris configuration where the angle cannot be opened by indentation, but patients must be counselled about its potential to cause permanent pupil dilation, Dr Thygesen said. Anterior chamber paracentesis rapidly lowers intraocular pressure (IOP) and immediately relieves symptoms, as well as preventing further optic nerve and trabecular meshwork damage secondary to acutely elevated IOP. However, it can lead to choroidal changes due to the sudden IOP decrease. Goniosynechialysis is an option for removing peripheral anterior synechiae of recent onset and if the cornea is clear. Trabeculectomy is associated with a lot of complications in eyes with ACG, including an elevated risk of failure compared with its use for POAG. The EAGLE study addressed the need for evidence about lens extraction as a treatment for PAC/PACG. It enrolled patients with PACG with IOP >21mmHg or PAC with IOP ≥30mmHg. Other eligibility criteria required angle-closure, either appositional or synechial in 180° or more, phakic status with absence of cataract, age 50 years or older, and diagnosis within six months. The EAGLE study found that initial treatment with lens extraction was more effective and cost-effective than laser iridotomy with medical therapy. Based on the outcomes, the investigators concluded that lens extraction may be considered as an alternative to current practice, Dr Thygesen said. However, they also observed that there is an increased risk of posterior capsule rupture when performing lens extraction in eyes with angle-closure, and that the results of EAGLE are not applicable to other types of PACs/PACGs. Dr Thygesen noted that EAGLE had other limitations, and he cautioned that one good quality trial may not be enough to change policy. “For sure we should still be doing primary iridotomy. Cataract surgery alone may be considered in some mild cases, and the results of the EAGLE study say the same. However, we do not need to do lens extraction in all cases,” Dr Thygesen said. John Thygesen: john.thygesen@regionh.dk