The patient with impaired vision represents a challenge to eye-care professionals. Whether temporary or permanent, low vision is the consequence of an eye disorder, and ophthalmologists and optometrists have a responsibility to manage it. If the outcome of optimal medical and surgical intervention is diminished functional vision, the patient needs vision rehabilitation (see also Chapter 25). No person with low vision should have to search far and wide for low-vision care. Some level of care should be integrated into every ophthalmic practice, either on-site or by referral to a low-vision center.
Low-vision patients typically have impaired visual performance: their visual acuity is not correctable with conventional glasses or contact lenses. They may have cloudy vision, constricted field of vision, large visual field defects (scotomas), glare sensitivity, abnormal color perception, diminished contrast, or diplopia. Patients are often confused by overlapping but dissimilar images from each eye.
The term “low vision” covers a wide range of visual problems, ranging from near-normal vision to severe loss. All low-vision patients have some degree of useful vision even though the loss may be profound. They should not be considered “blind” unless they no longer have useful visual clues. Performance varies with each individual.
In the United States, over 6 million persons are visually impaired but not classified as legally blind.1 Over 75% of patients seeking treatment are age 65 or older. Age-related macular degeneration accounts for an increasing number of cases. Other common causes of low vision are glaucoma, diabetic retinopathy, cataract, optic atrophy, corneal disease, cerebral damage, degenerative myopia, and retinitis pigmentosa. Approximately 9% of the low-vision population is pediatric, with visual loss from congenital eye disorders or trauma. (See Chapter 20 for discussion of the worldwide prevalence and causes of visual impairment.)
Effective low-vision intervention starts as soon as the patient experiences difficulty performing ordinary tasks. A treatment plan should consider the level of function, realistic goals for intervention, and the varieties of devices that could be helpful. Patients must face the fact that impaired vision is usually progressive. The sooner they adapt to low-vision devices, the sooner they can adjust to the new techniques of using their vision. Low-vision evaluation should never be delayed unless the person is in an active phase of medical or surgical treatment.
Visual performance can be improved by optical and nonoptical devices. The general term for corrective devices is “low-vision aids.” In this chapter, the emphasis will be on assessment techniques, descriptions of useful devices, and a discussion of some of the functional aspects of common eye diseases.
1Legal blindness—defined as best corrected visual acuity of 20/200 or less in the better eye or a visual field of 20° or less—affects 1,000,000 individuals in the United States (see Chapter 20). It is an administrative definition that does not mean that the patient is unable to see anything.