Normal vision is the ability to see comfortably what is around us, whether far away or near, with or without glasses. This is vision around 6/6 (20/20). Almost everyone can continue to manage their activities when changes in vision are small.
For low vision, the following two definitions are in use:
- Low vision is visual acuity less than 6/18 and equal to or better than 3/60 in the better eye with best correction (WHO).
- A person with low vision is one who has impairment of visual functioning even after treatment and/or standard refractive correction, and has a visual acuity of less than 6/18 to light perception, or a visual field less than 10 degrees from the point of fixation, but who uses, or is potentially able to use, vision for the planning and/or execution of a task for which vision is essential (Low Vision Services or Care).
According to the most recent data available to WHO, there are an estimated 124 million people in the world with low vision. About a fourth of these would benefit from low vision services.
Low vision can result from a variety of diseases, disorders, and injuries that affect the eye. Many people with low vision have age-related macular degeneration, cataract, glaucoma, or diabetic retinopathy. Age-related macular degeneration accounts for almost 45 percent of all cases of low vision.
Low vision can occur at any age, but by far the greatest number of people who are partially sighted are the elderly. Low vision is most often due to a change in central vision. Occasionally it is associated with loss of side (peripheral) vision when it is close to centre. In a few cases it is associated with loss of colour vision or difficulty adapting to changes in brightness within the field of vision.
Low vision devices can help you make the most of your vision so that you can perform everyday tasks more easily and with less frustration. There are several different categories of low vision devices: optical devices, non-optical devices, and electronic magnifiers and magnifying systems. Low vision devices are task-specific, designed for close-up visual tasks or distance viewing. You may require several different devices to accomplish different tasks, depending upon your eye condition and your everyday living needs.
Low Vision Optical Devices
Low vision optical devices include a variety of helpful visual aids, including stand and hand-held magnifiers, strong magnifying reading glasses, loupes, and small telescopes. Because these devices can provide greatly increased magnification powers and prescription strengths, along with higher-quality optics (i.e. the way the lens bends or refracts light), they are different from regular glasses and magnifiers that you can buy in a local store or online. Most often they require training to help you use them effectively.
Low Vision Non-Optical Devices
Low vision non-optical devices can include adaptations such as reading stands, supplemental lighting, absorptive (or glare control) sunglasses, typoscopes, and tactile locator dots. They can be used in combination with low vision optical devices and can help with reading, organizing, labeling, and a variety of everyday tasks.
Electronic Magnifying Systems
Electronic magnifying systems come in many different varieties and sizes, depending upon the task or activity you want, or need, to do. Some have a camera system that displays a magnified image on a monitor, which can be helpful for reading mail, books, and magazines, while others are hand-held, portable, and can be taken to the supermarket to read labels and coupons, or to restaurants to read menus.