RISK FACTOR ASSESSMENT AND GLAUCOMA SCREENING

Abstract

Glaucoma, a collection of diseases that affect the optic nerve head and are associated with visual field loss, may be broadly classified as follows: primary open angle glaucoma (POAG), secondary open-angle glaucoma, primary angle-closure glaucoma (PACG), secondary angle-closure glaucoma, congenital glaucoma, and juvenile glaucoma. All of these diseases are associated with irreversible blindness. Thus, the public health importance of detecting undiagnosed and treatable glaucoma is important, as blindness has economic and societal consequences for the rest of an individual's life. 97 In this review the main focus is on POAG and PACG; some of the information on risk factor assessment and screening of POAG and PACG is relevant to the secondary glaucomas. POAG is characterized by glaucomatous optic nerve damage and visual field loss in the presence of open and normal-appearing anterior chamber angles and the absence of other known causes of glaucoma. It has an adult onset, is usually bilateral, and has no symptoms until late in the disease when patients lose their central vision. 79 It is the third leading cause of blindness worldwide 107 and has an age-adjusted prevalence of 1.55%. 112 Extrapolations to the year 2000, using estimates of glaucoma prevalence from earlier population-based survey data, place the worldwide population of people with POAG at approximately 68 million. 81 In Olmsted County, Minnesota, 9% of subjects with a mean age of 66 years at the time of glaucoma diagnosis 40 were bilaterally blind at the 20 year follow-up, despite glaucoma treatment. Patients with PACG may or may not have optic nerve damage. PACG is defined as the closure of the anterior chamber angle by relative pupillary block, which is the obstruction of the trabecular meshwork by the peripheral iris. 79 The iris is bowed forward because of the inability of the aqueous humor to pass easily into the anterior chamber from the posterior chamber. Patients with PACG may present acutely with elevated intraocular pressures, a mid-dilated pupil, and a red eye and with nausea and vomiting. Not infrequently they may have no complaints or complain only of a nonspecific headache, eye pain, or halos around lights. 79 PACG is more prevalent in Asia, whereas POAG has a more even distribution throughout the world. 81 Because most patients with glaucoma, except for those with PACG attacks, are asymptomatic, screening for glaucoma is considered to be a worthwhile societal goal if the cost is not too great. 99 Because the prevalence of glaucoma is low in the general population, screening for glaucoma would be more cost effective in populations with risk factors for glaucoma as it would result in more cases of glaucoma being detected. Thus, prior to reviewing the issues of screening for glaucoma, the authors first define risk factors and then discuss the known risk factors for POAG and PACG.