Redefining POAG

To better diagnose and treat patients, primary open-angle glaucoma (POAG) should be redefined in terms of several identifiable subtypes, Louis R Pasquale MD, FARVO, of Harvard Medical School, Boston, USA, told Glaucoma Subspecialty Day at the 2016 American Academy of Ophthalmology Annual Meeting in Chicago, USA. “POAG 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. Biochemical markers specific to each subtype also point to specific biochemical pathways that may be successfully targeted for treatment. PC-OAG 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. 16mmHg is a high number for these patients. PC-OAG appears to be related to nitric oxide (NO) signalling, and patients should be encouraged to eat foods with nitrates such as leafy green vegetables. Medications targeting NO are in development, Dr Pasquale added. AD-OAG African-derived OAG, or AD-OAG, appears in young patients and progresses quickly, sometimes leading to blindness in patients in their third and fourth decades, Dr Pasquale said. AD-OAG is seen mostly in patients of African descent, with one study finding almost 21% of those 20 to 40 years of age with IOP of 24mmHg or higher, or cup-to-disc ratio of 0.7 or more in one eye. AD-OAG should be screened for and treated early. Siblings and children of patients should be screened. ED-OAG 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% of glaucoma patients in some populations, Dr Pasquale noted. Pressures of 35 or higher are rare for POAG types, and may indicate steroid exposure or secondary glaucoma. In cases of rapidly progressing glaucoma, diurnal curves should be taken and neuroimaging considered. More study is needed to determine the nature of the various subtypes and treatments for them, but recognising they exist is a good start, Dr Pasquale concluded. “Let’s help our patients by taking the ‘P’ out of POAG.” Louis R Pasquale: louis_pasquale@meei.harvard.edu