Impaired Vision: Refractive Errors, Low Vision and Blindness

Impaired Vision

REFRACTIVE ERRORS

In refractive errors, vision is impaired because a shortened or elongated eyeball prevents light rays from focusing sharply on the retina. Blurred vision from refractive error can be corrected with eyeglasses or contact lenses. The appropriate eyeglass or contact lens is determined by refraction. Refraction ophthalmology con-sists of placing various types of lenses in front of the patient’s eyes to determine which lens best improves the patient’s vision.

The depth of the eyeball is important in determining refractive error (Fig. 58-6). Patients for whom the visual image focuses pre-cisely on the macula and who do not need eyeglasses or contact lenses are said to have emmetropia (normal vision). People who have myopia are said to be nearsighted. They have deeper eye-balls; the distant visual image focuses in front of, or short of, the retina. Myopic people experience blurred distance vision. When people have a shorter depth to their eyes, the visual image focuses beyond the retina; the eyes are shallower and are called hyperopic. People with hyperopia are farsighted. These patients experience near vision blurriness, whereas their distance vision is excellent.

Another important cause of refractive error is astigmatism, an irregularity in the curve of the cornea. Because astigmatism causes a distortion of the visual image, acuity of distance and near vision can be decreased. Eyeglasses with a cylinder correction or rigid or soft toric contact lenses are appropriate for these patients.

LOW VISION AND BLINDNESS

Low vision is a general term describing visual impairment that re-quires patients to use devices and strategies in addition to correc-tive lenses to perform visual tasks. Low vision is defined as a best corrected visual acuity (BCVA) of 20/70 to 20/200 (Table 58-1).

Blindness is defined as a BCVA of 20/400 to no light per-ception. The clinical definition of absolute blindness is the ab-sence of light perception. Legal blindness is a condition of impaired vision in which an individual has a BCVA that does not exceed 20/200 in the better eye or whose widest visual field di-ameter is 20 degrees or less. This definition does not equate with functional ability, nor does it classify the degrees of visual im-pairment. Legal blindness ranges from an inability to perceive light to having some vision remaining. An individual who meets the criteria for legal blindness may obtain government financial assistance. There are more than 1,046,000 legally blind Ameri-cans who are 40 years of age or older. African Americans have a higher rate of blindness than do Caucasians (Preshel & Prevent Blindness America, 2002).

Impaired vision is accompanied by difficulty in performing functional activities. Individuals with visual acuity of 20/80 to 20/100 with a visual field restriction of 60 degrees to greater than 20 degrees can read at a nearly normal level with optical aids. Their visual orientation is near normal but requires increased scanning of the environment (ie, systematic use of head and eye movements). In a visual acuity range of 20/200 to 20/400 with a 20-degree to greater than 10-degree visual field restriction, the individual can read slowly with optical aids. 

His or her visual orientation is slow, with constant scanning of the environment; individuals in this category have travel vision. Individuals with hand motion vision or no vision may benefit from the use of mo-bility devices (eg, cane, guide dog) and should be encouraged to learn Braille and to use computer aids.

The most common causes of blindness and visual impairment among adults 40 years of age or older are diabetic retinopathy, macular degeneration, glaucoma, and cataracts, (Preshel & Pre-vent Blindness America, 2002). Macular degeneration is more prevalent among Caucasians, whereas glaucoma is more preva-lent among African Americans. Age-related changes in the eye are described in Table 58-2.

Low-Vision Assessment

The assessment of low vision includes a thorough history and the examination of distance and near visual acuity, visual field, contrast sensitivity, glare, color perception, and refraction. Specially de-signed, low-vision visual acuity charts are used to evaluate patients.

PATIENT INTERVIEW

During history taking, the cause and duration of the patient’s vi-sual impairment are identified. Patients with retinitis pigmentosa, for example, have a genetic abnormality. Patients with diabetic macular edema typically have fluctuating visual acuity. Patients with macular degeneration have central acuity problems. Central acuity problems cause difficulty in performing activities that re-quire finer vision, such as reading. People with peripheral field defects have more difficulties with mobility. The patient’s cus-tomary activities of daily living, medication regimen, habits (eg, smoking), acceptance of the physical limitations brought about by the visual impairment, and realistic expectations of low-vision aids must also be identified. These aspects of the patient’s activi-ties are important indicators for planning care that will include guidelines for safety and referrals to social services.

ASSESSMENT

Contrast-sensitivity testing measures visual acuity in different de-grees of contrast. The initial test may take the form of simply turning on the lights while testing the distance acuity. If the pa-tient can read better with the lights on, the patient can benefit from magnification. Glare testing enables the examiner to obtain a more realistic evaluation of the patient’s ability to function in his or her environment. Glare can reduce a person’s ability to see, especially in patients with cataracts. Devices that test glare, such as the Brightness Acuity Tester, produce three degrees of bright light to create a dazzle effect while the patient is viewing a target, such as Snellen letters on the wall. The lights have been calibrated to imitate certain objects that create glare, such as the brightness of a car’s headlights at night.

Medical Management

Managing low vision involves magnification and image enhance-ment through the use of low-vision aids and strategies and through referrals to social services and community agencies serv-ing the visually impaired. The goals are to enhance visual func-tion and assist patients with low vision to perform customary activities. Low-vision aids include optical and nonoptical devices (Table 58-3). The optical devices include convex lens aids, such as magnifiers and spectacles; telescopic devices; anti-reflective lenses that diminish glare; and electronic reading systems, such as closed-circuit television and computers with large print. Contin-uing advances in computer software provide very useful products for patients with low vision. Scanners teamed with the appro-priate software enable the user to scan printed data into the computer and have it read by computer voice or to increase the magnification for reading. Magnifiers can be hand-held or at-tached to a stand with or without illumination. Telescopic de-vices can be spectacle telescopes or clip-on or hand-held loupes.

Nonoptical aids include large-print publications and a variety of writing aids. The Internet continues to expand, and a tele phone system has been developed that allows access to the Inter-net and e-mail using voice commands (see Chart 58-2).

Strategies that enhance the performance of visual tasks in-clude modification of body movements and illumination and training for independent living skills. Head movements and positions can be modified to place images in functional areas of the visual field. Illumination is an added feature in magnifiers. Adjusting the lighting helps with reading and other activities. Simple optical and nonoptical aids are available in low-vision clinics.

Referrals to community agencies may be necessary for low-vision patients living alone who are unable to self-administer their medications. Community agencies, such as The Lighthouse National Center for Vision and Aging, offer services to low-vision patients that include training in independent living skills and the provision of occupational and recreational activities and a wide variety of assistive devices for vision enhancement and orienta-tion and mobility.

VISION RESTORATION FOR THE BLIND

Ophthalmologists have worked toward visual restoration for blind individuals for years, and computer technology now pro-vides opportunities for restoring sight. For example, a multiple-unit artificial retina chipset (MARC) has been devised for implanting within the eye. The MARC can be enabled to receive signals from an external camera mounted in a glasses frame. The acquired image is wirelessly transmitted to the chip, which pro-vides a type of artificial vision and which, with training, allows the patient to achieve some useful vision. Although the device is still experimental, some work has been done with patients who have lost vision from retinitis pigmentosa and age-related macu-lar degeneration (Humayan et al., 1999).

Nursing Management

Coping with blindness involves three types of adaptation: emo-tional, physical, and social. The emotional adjustment to blind-ness or severe visual impairment determines the success of the physical and social adjustments of the patient. Successful emo-tional adjustment means acceptance of blindness or severe visual impairment.

PROMOTING COPING EFFORTS

Effective coping may not occur until the patient recognizes the permanence of the blindness. Clinging to false hopes of regain-ing vision hampers effective adaptation to blindness. A newly blind patient and his or her family members (especially those who live with the patient) undergo the various steps of grieving: de-nial and shock, anger and protest, restitution, loss resolution, and acceptance. The ability to accept the changes that must come with visual loss and willingness to adapt to those changes influence the successful rehabilitation of the patient who is blind. Additional aspects to consider are value changes, independence–dependence conflicts, coping with stigma, and learning to function in social settings without visual cues and landmarks.

PROMOTING SPATIAL ORIENTATION AND MOBILITY

People who are blind detect and incorporate less information about their environment than do sighted people. The blind per-son relies on egocentric, sequential, and positional information, which centers on the person and his or her relationship to the ob-jects in the environment. For example, the topographic concepts of front, back, left, right, above, and below and measures of dis-tances are most useful in determining the exact position, se-quence, and location of objects in relation to the person who is blind. Although their basis of information may be different from that of sighted people, people who are blind can comprehend spa-tial concepts.

The goal of orientation and mobility training is to foster in-dependence in the environment. Training may be accomplished by using auditory and tactile cues and by providing anticipatory information. Having a concept of the spatial composition of the environment (ie, cognitive map) enhances independence of those who are blind. Orientation and mobility training programs are offered by community agencies serving the blind or visually im-paired. Training includes using mobility devices for travel, the long cane, electronic travel aids, dog guides, and orientation aids. The basic orientation and mobility techniques used by a sighted person to assist a person who is blind or visually impaired to am-bulate safely and efficiently are called sighted-guide techniques.

Spatial Orientation and Mobility in Institutional Settings.A blindor severely visually impaired patient requires strategies for adapt-ing to the environment. The monocular postoperative patient whose functioning eye is restricted by a surgical patch or by post-operative inflammation requires early ambulation just like any postoperative patient. The activities of daily living, such as walking to a chair from a bed, require spatial concepts. The patient needs to know where he or she is in relation to the rest of the room, to understand the changes that may occur, and how to approach the desired location safely. This requires a collaborative effort be-tween the patient and the nurse, who serves as the sighted guide.

Patients whose visual impairment results from a chronic pro-gressive eye disorder, such as glaucoma, have better cognitive mapping skills than the suddenly blinded patient. They have de-veloped the use of spatial and topographic concepts early and gradually; hence, remembering a room layout is easier for them. Suddenly blinded patients have more difficulty in adjusting; and emotional and behavioral issues of coping with blindness may hinder their learning. These patients require intensive emotional support. The nurse must assess the degree of physical assistance the patient with a visual deficit requires and communicate this to other health care personnel.

The food tray’s composition is likened to the face of a clock. For example, the main plate may be described as being at 12 o’clock or the coffee cup at 3 o’clock. In the hospital, the bedside table and the call button must always be within reach. The parts of the call button are explained, and the patient is encouraged to touch and press the buttons or dials until the activity is mastered. The patient must be familiarized with the location of the telephone, water pitcher, and other objects on the bedside table. All articles and furniture must be replaced in the same positions. Introducing oneself on entering a patient’s room is always a polite gesture and helps in the orientation of a blind patient.

The nurse should be aware of the importance of technique in providing physical assistance, developing independence, and en-suring safety. The readiness of the patient and his or her family to learn must be assessed before initiating orientation and mobil-ity training.

Teaching Patients Self-Care.The nurse, social workers, family,and others collaborate to assess the patient’s home condition and support system. If available, a low-vision specialist should be con-sulted before discharge, particularly for patients for whom iden-tifying and administering medications pose problems. The level of visual acuity and patient preference help to determine appro-priate interventions. For example, a plastic pill container with di-viders that has been prefilled with a week’s supply of medication can make medication administration easier for some patients, whereas others may prefer to have medication bottles marked with textured paints. Many patients require referral to social ser-vices. Patients with habits that may jeopardize safety, such as smoking, need to be cautioned and assisted to make their envi-ronment safe.

Community Programs and Services.In the United States, lawssuch as the Rehabilitation Act, the Civil Rights Act, and the Americans With Disabilities Act support assistance of the blind. Governmental services include income assistance through Social Security Disability Income and Supplemental Security Income; health insurance through Medicaid and Medicare programs; support services, such as vocational rehabilitation programs of-fered by the Division of Blind Services; tax exemptions and tax deductions; Department of Veterans Affairs programs for visually impaired veterans; and U.S. Postal Service reduced postage for Braille materials and talking books.