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Chapter-4.1 Definition and Magnitude of Low Vision

BOOK TITLE: Postgraduate Ophthalmology (2 Volumes)

Author
1. Ghoshal Rituparna
ISBN
9789350252703
DOI
10.5005/jp/books/11051_8
Edition
1/e
Publishing Year
2012
Pages
15
Author Affiliations
1. Nagar School of Optometry, Nagri Municipal Eye Hospital, Ellis Bridge, Ahmedabad, Gujarat, India; Sankara Eye Hospital, Anand, Gujarat, India
Chapter keywords
visual impairment, low vision, blindness, corneal scarring, congenital rubella, ophthalmic neonatorum, vision rehabilitation organizations, private optometric and ophthalmic practices, comprehensive low vision services, central field loss, visual functions, near visual acuity, contrast sensitivity, blurred vision, eccentric viewing training, magnification, glare comfort devices, glaucoma, lasered diabetic retinopathy, optical LVDs, spectacle magnifier, stand magnifier, hand-held magnifier, convex lens, angular magnification, relative distance magnification, electronic low vision devices, electronic optical systems, projection magnification, tinted glasses, filters, visors, albinism, rod cone monochromatism, vision, sensory substitution devices, audio books, Braille, Notex, needle threader, color identifier

Abstract

Visual impairment includes both low vision and blindness. In developing countries, major causes of blindness are corneal scarring because of vitamin A deficiency, congenital rubella, ophthalmic neonatorum, and so on. Hospitals, vision rehabilitation organizations, and private optometric and ophthalmic practices provide comprehensive low vision services. In central field loss, different visual functions affected are visual fields, distance and near visual acuity, and contrast sensitivity. Management of overall blurred vision includes eccentric viewing training, magnification, contrast enhancing measures, and glare comfort devices. Condition causing PFL rarely cause glare except diseases, such as glaucoma, lasered diabetic retinopathy, and so on. For near, there are mainly three types of optical LVDs, such as spectacle magnifier, stand magnifier, and hand-held magnifier. A stand magnifier is a convex lens, where both angular magnification and relative distance magnification is used. Electronic low vision devices are electronic optical systems that make the object appear larger. The principle of projection magnification is used here. Use of tinted glasses, filters, and visors provide great comfort in situations of glaucoma, albinism, and rod cone monochromatism. When vision is affected, the loss is compensated using other residual senses. Some of the sensory substitution devices are audio books, and Braille. Notex, needle threader, color identifier, and talking clock and watch are discussed.

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