The vast majority of blindness is avoidable. The World Health Organization (WHO) estimates that 80% of cases of visual impairment could be prevented or reversed with early diagnosis and treatment. The leading causes of visual impairment are cataract and refractive error, followed by glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy (DR). Loss of vision from these conditions is not inevitable; however, identifying cases early and linking cases with appropriate care remain significant challenges. To address the global burden of avoidable blindness, eye care systems must determine optimal strategies for identifying people with or predisposed to visual impairment beyond opportunistic screening. Outreach programs can prevent blindness both by screening for asymptomatic disease like age-related macular degeneration (AMD), diabetic retinopathy (DR), and glaucoma and case detection of symptomatic disease like cataract and refractive error. Eye care systems have developed numerous approaches to these identification methods, including screening using telemedicine and case detection via cataract camps or health worker models, but no studies have been conducted on the comparative effectiveness or cost effectiveness of these various approaches. Technology promises to greatly improve access to sophisticated eye care. AMD, DR, and glaucoma can result in irreversible vision loss, and early diagnosis and effective treatment can prevent progression. Thus, mass screening programs may prevent progression and improve the vision of a population. However, mass screening for eye disease is currently not recommended. Although self-evident that early detection can prevent blindness for an individual, no randomized controlled trial has been able to demonstrate that screening improves visual acuity at the regional level. However, recent technological advances promise to dramatically change the equation by allowing non-medical personnel to use mobile, easy-to-use retinal imaging devices to diagnose screenable eye diseases such as AMD, DR, and glaucoma. Mobile technology could also transform the way clinics communicate with their patients, improving linkage to and retention in care. Optical coherence tomography (OCT) is an ideal test for screening. OCT can be performed through an undilated pupil and is less subject to optical aberrations due to cataract than is fundus photography. OCT machines have pre-installed algorithms to screen for glaucoma, and major anatomical abnormalities can easily be detected even by novice technicians. The infrared image allows detection of referable diabetic retinopathy, and newer OCT angiography machines offer even more discrimination of early diabetic retinopathy. OCT machines are ever more portable, and could be feasibly used in mobile screening programs. The investigators propose a large cluster-randomized trial to compare two population level blindness prevention programs: (1) a state-of-the-art screening program employing OCT, fundus photography, and intraocular pressure testing to screen for glaucoma, DR, and AMD followed by enhanced linkage-to-care to the local eye hospital, and (2) a screening program involving only visual acuity assessment. An initial door-to-door census will assess baseline visual acuity in both study arms. The investigators will compare visual acuity between the two arms through a second door-to-door census 9 years later (primary outcome).