POAG must be redefined

To better diagnose and treat patients, primary open-angle glaucoma (POAG) should be redefined in terms of several identifiable sub-types, Louis R Pasquale MD, of Harvard Medical School, Boston, USA, told Glaucoma subspecialty day at the 2016 AAO Annual Meeting in Chicago, USA. “PAOG is a remarkably heterogeneous disease with distinct but overlapping subtypes,” Dr Pasquale said in his American Glaucoma Society Lecture. Each has its own distinct age of onset, intraocular pressure (IOP) profile and structural optic nerve features, and biochemical markers point to specific biochemical pathways. Paracentral OAG, or PC OAG, in which vision loss is mainly in the paracentral region, is marked by low IOP and difficulty keeping IOP low enough to prevent progression, Dr Pasquale said. “16mm Hg is a high number for these patients.” PC OAG appears to be related to nitric oxide signalling, and patients should be encourage to eat foods with nitrates such as leafy green vegetables. Medications targeting NO are in development. African-derived OAG, or AD OAG, progresses quickly and appears in young patients, with one study of patients of African descent showing 20.9 per cent of those 20-40 years of age had IOPs of 24mm Hg or greater or cup to disc ratio of 0.7 or greater in one eye. It needs to be screened and treated early, and siblings and children of patients should be screened. Estrogen-derived OAG, or ED OAG, appears related to lower lifetime exposure to estrogen, with late menarche, oral contraceptive use, early menopause and early oophorectomy risk factors, Dr Pasquale said. Overall, high IOP is not a reliable marker for POAG with normal IOP observed in up to 90 per cent of glaucoma patients in some populations, Dr Pasquale noted. Pressures of 35 or higher are rare, and may indicate steroid exposure, physical pressure such as excessive eye rubbing, or secondary glaucoma. In cases of rapidly progressing glaucoma, diurnal curves should be taken and neuro-imaging considered. More study is needed to determine the subtypes and treatments for them, Dr Pasquale concluded. “Let’s help our patients by taking the ‘P’ out of PAOG.”