Chapter 3

Vision Rehabilitation: Care and Benefit Plan Models: Literature Review

Vision Rehabilitation: Care and Benefit Plan Models: Literature Review

Behavioral Modification and Social Support

The psychosocial aspects of low vision are increasingly recognized as important to the rehabilitation process. The American Academy of Ophthalmology21 notes that many individuals with vision loss experience feelings of depression, fear, isolation, loss of independence, inadequacy and anger, and therefore may benefit from organized support groups or counseling. Attitudes affect adaptability, particularly when vision impairment onset occurs in adulthood.61 Small support group interaction appears to be effective, based on attitudinal outcomes and perceptions of activity levels.34

A recent RCT of a self-management group intervention in 92 elderly adults with low vision due to AMD found that a 6-week behavioral intervention could significantly reduce psychological distress in this population.66 Subjects assigned to the intervention group experienced improved mood and self-efficacy and increased their use of vision aids in comparison to the control group. The intervention consisted of six weekly, 2-hour group sessions providing education about AMD, group discussion, and behavioral and cognitive skills training to address barriers to independence. One limitation of this study is the lack of followup with study participants; it is unclear if these encouraging results were maintained beyond the limited period of observation without additional intervention.

Conrod and Overbury evaluated the effects of three interventions on visual functioning (perceptual measures) and beliefs about vision loss (psychosocial measures) in 49 elderly persons. Participants were randomized to four groups, including the three interventions, i.e., perceptual training, individual counseling, group counseling, and a control group with no intervention. The study design compared pre- and post-test results for each group, and with changes in the control group. The results indicated that the perceptual training and individual counseling groups improved significantly on perceptual measures, but that the group counseling arm of the study did not do better than the control group. Also, the individual counseling and group counseling groups improved significantly over the course of the study on psychosocial measures, but the perceptual training and control groups did not. The intervention effects persisted 3 to 6 months after the interventions.67

A pre-post evaluation of the psychosocial and functional outcomes of nearly 400 persons receiving group independence training (as opposed to traditional one-on-one independence training) found that the intervention had a positive effect on self-reported psychosocial indicators.68 However, because the intervention was not standardized and the study relied only on historical controls, this finding is not definitive regarding the effectiveness of the group model.

Focus groups conducted in Sweden on the design of a health education program for individuals with AMD indicated that patients require more information about AMD, need information regarding strategies to improve activities of daily living, and want programs to provide support and problem-solving strategies.69 A major barrier to service utilization is the perception among patients that AMD is a natural part of the aging process, not a condition to be treated or otherwise managed.

Low vision services in general (i.e., clinical exam and prescription of optical and/or non-optical devices with appropriate training) were shown to be associated with having a positive effect on depression in a pre-post study of 155 visually impaired elderly men and women.70 This unpublished study also found that counseling increased the life satisfaction of subjects. Currently, a longitudinal, observational study is being conducted to assess the relationships among disability, depression, and rehabilitation in 600 visually impaired elderly people. It will examine the course of depression over 18 months as it affects, and is affected by, impairment severity, functional ability, and rehabilitation service utilization.71

Qualitative research has been conducted to identify critical elements in rehabilitation. Based on the experiences of those in the field, a 1995 National Summit on Employment and Underemployment, sponsored by the American Federation for the Blind, identified the following critical elements of successful vocational rehabilitation:34

  • Partnerships between corporate officials and rehabilitation clients and providers.
  • Public policy based on relevant, uniform demographic data.
  • National programs to increase the public's understanding of the abilities of the visually impaired.
  • Equal access to information through technology.
  • Training for personnel that is reality-based.
  • Focus on employment outcomes.
  • Client training in self-advocacy, leadership, risk taking, and responsibility.
  • Career education programs for children and youth.
  • Ongoing training and development.

It is unclear what evidence was used by participants in the summit to identify these elements. Also unclear is whether these elements have the potential to affect any health or social outcomes.

Focus group research conducted by the Oregon Commission for the Blind identified the importance of positive attitudes; networking; the role of role models, mentors, and peers; and openness to vocational choices for successful employment. Clients identified the importance of the following:42

  • Positive attitudes.
  • Adaptation to the sighted world.
  • Proficiency in adaptive techniques.
  • The use of mentors and role models for successful employment.

While focus groups may provide insight into setting research agendas for the future, findings from focus groups alone provide little evidence for the effect of services on outcomes.

Models of Delivery

The evidence base for the effectiveness of vision rehabilitation services is, at best, only emerging. Massof and Lidoff provide an overview of different vision rehabilitation service delivery models, including those of the VA, the Jewish Guild for the Blind, and Lions Low Vision Service among others.72 However, there is only sparse evidence for the effectiveness of different models of vision rehabilitation service delivery, i.e., the different settings of care, different methods of paying or reimbursing for care, and other factors related to models of care. Zambone and Cox Suarez note that "the greatest challenge to service delivery is the dearth of research-based models and practices."73

A number of studies have measured the outcomes of low vision care but these have usually been longitudinal case series, thus constituting very low quality of evidence for effectiveness. To date, there have been no RCTs that have evaluated the effectiveness and cost effectiveness of different models of care in low vision. The size of the low vision population and the paucity of systematic evaluation have created a pressing need for evidence about cost-effectiveness in order to inform service developments for low vision rehabilitation.

A review of the literature on the value of low-vision services published by Raasch et al. in 1997 examined reports made between 1986 and 1996 of 16 studies of interventions conducted in low vision clinics, hospitals, and other settings.74 The reviewers find that these and similar studies have reported "success" with low-vision aids, ranging from 23 percent to 100 percent, and that this wide range stems from the different types of interventions used and different definitions of success. However, Raasch et al. note that "Numerous examples of successful rehabilitation can be recounted, but—despite the strong anecdotal evidence of the value of low-vision rehabilitation—there are relatively few studies that quantify the type and magnitude of the effect of this intervention." They go on to find that "No prospective controlled studies have clearly established the effectiveness of the systematic delivery of low-vision care to a large sample of visually impaired subjects, and no previous studies have demonstrated the impact of low-vision care on quality of life." Among the 16 studies cited in the review, there were widespread methodological weaknesses. Two of the studies were unpublished; only two were described as being prospective; seven specified no followup period; 11 had no performance measures; and 13 had no quality of life measures. Raasch et al. indicate that there is indirect evidence of effectiveness of low-vision rehabilitation, in the form of patient satisfaction and frequency and type of low-vision aid use. In particular, a clear need has been found for training in low-vision aid use. Among other findings, the value of eccentric viewing training (training to increase the ability to utilize a portion of the peripheral retina for tasks such as reading and mobility) is not as clear. The positive effect of rehabilitation on reading was not dependent on the type of diagnosis. However, the delivery approach, scope of services, and training of providers have not been definitively evaluated. As such, a determination cannot be made regarding the effectiveness of these service providers and settings relative to other models of delivery.

A recent RCT examined the impact of a set of vision rehabilitation services, including optometry, occupational therapy, and social work services, on patients' functional status. All 97 patients in the study received this set of services, although they were randomized to individually-focused services or family-focused services. Pre- and post-intervention data were collected for functional status, assessed by speed and accuracy of performance (objective measure) and by patients' self-reports of difficulty and dependency in performing daily activities (subjective measure). Patients in both groups showed significant improvements in both measures of function. However, the sample size was too small to detect any significant difference in function due to the use of individual- versus family-focused services.75

Leat et al. (1994) surveyed 57 elderly patients attending a low vision clinic, and found that almost 90 percent reported benefits of attending the clinic, and 81 percent of patients were regularly using low vision aids. Perceived benefit from visiting the clinic was strongly associated with ability to perform daily living tasks and improve reading; there was some association between perceived benefit and frequency of using low vision aids, but not with duration of use.76

Currently, an RCT is being conducted to explore integrated versus optometric low vision rehabilitation for patients with AMD in England. The interventions assessed will include:

  • Conventional hospital-based low vision care.
  • Hospital-based care integrated with home-based care by a low vision rehabilitation provider.
  • Hospital-based care and non-vision-specific intervention at home from a community care worker.

Outcomes will be assessed at recruitment and 12 months post-intervention, using low vision specific and generic quality of life measures, patterns of low vision aid use, and task performance.77

Some unpublished preliminary findings are available regarding the effectiveness of the different delivery models within the VA. De l'Aune and Williams analyzed and reported on data from more than 3,000 visually impaired persons who received vision rehabilitation services through one of the following three delivery models: 1) VA residential programs, 2) VA Blind Rehabilitation Outpatient Services (VA-BROS), and 3) non-VA programs.78,79 (See De l'Aune et al (1999)48 for a description of the methods of this project and the reliability and validity of the survey instrument.) Veterans received more specific vision rehabilitation training in the inpatient program compared to the outpatient program. Data on functional outcomes were collected for a subset of the 3,000 subjects in each of the three models of rehabilitation, and the pre-rehabilitation measure was collected retrospectively, i.e., the client was asked to respond as if the survey were taking place prior to the rehabilitation experience.

The available data pointed to a positive association between self-reported functional outcomes and inpatient and outpatient rehabilitation. Self-perceived change in independence was measured on four components, including orientation and mobility skills, manual skills, low vision functionality, and instrumental activities of daily living (IADL). This measure of function change showed a 30 percent average change for the residential program (n=1,193), a 5 percent average change for the VA BROS (n=31), and an 8 percent average change for non-VA rehabilitation (n=212). Satisfaction levels were high and the same (98 percent) for VA and non-VA programs.

It is unclear what the relative effects are of the respective components of the VA package of services. Inpatient and outpatient vision rehabilitation within the VA are coordinated with general health services. Therefore, the degree to which functional improvements result from the vision rehabilitation services themselves, rather than from medical services such as diabetes management, is unclear. Moreover, the cost-effectiveness of the functional outcome gains achieved through vision rehabilitation within the VA is unknown. Because VA services are provided within a largely closed system with a global budget, rehabilitation costs are not individually tracked. However, VA studies have shown that hours of vision rehabilitation service are correlated to percent functional gain.

Various health care personnel that may be involved in the rehabilitation of an individual with vision impairment include:21,28

  • Ophthalmologist.
  • Optometrist.
  • Occupational therapist.
  • Physical therapist.
  • Orientation and mobility specialist.
  • Rehabilitation teacher.
  • Psychologist.
  • Social worker.
  • Ophthalmic assistant.

Vision rehabilitation can take place in numerous settings, including ophthalmology and optometry offices, rehabilitation hospitals, university-based clinics, schools, State agencies, private agencies, veterans administration programs, charitable agencies and independent living centers.21,28 Home modification is also an important rehabilitation activity, but is outside of the realm of some providers (e.g., ophthalmologists). As demonstrated by a recent review of center-based services, home-based services, and other service delivery systems, the type of service delivery system may define or limit the provision of individualized services. As such, the structure of delivery affects the processes of care.80 While a multidisciplinary approach to care is intuitively appealing given the potential to increase coordination among providers and settings, no study has rigorously evaluated the potential benefit of a multidisciplinary approach.

The following sections describe the process of vision rehabilitation in different settings of care.

Residential Nursing Home

More than two-thirds of visually impaired adults are age 65 and older. As such, accurate diagnosis of vision impairment in the nursing home population will identify individuals who can benefit from rehabilitation services. Therefore, it is important to train nursing home staff to recognize impaired vision and to implement practical interventions to improve patients' functioning levels.41,56

Limited Hospital Stay

Inpatient settings may be appropriate for individuals in whom vision loss is diagnosed as a secondary disability. Specifically, skilled nursing and extended care facilities provide rehabilitation to individuals with several types of physical impairment, including vision loss. Similarly, rehabilitation centers (including acute care hospitals and subacute units) may address visual impairment in conjunction with other disabilities.28

Hospital and rehabilitation facilities have begun to establish low vision rehabilitation programs as part of their outpatient rehabilitation services in an effort to meet the growing demand for these services. The passage of pending legislation that would provide Medicare coverage for low vision occupational therapy services could provide an incentive for development of these programs.28

Provider Office

Most vision loss is attributable to disease. Therefore, it will be important for physicians and other health care providers to have the awareness, skills, and resources available to address secondary vision loss in their patients. Rehabilitation can be performed in an office setting, but specialized low vision rehabilitation centers may offer a wider range of equipment.21 Although ophthalmologists play an important role in diagnosing and prescribing optical devices and making referrals, few ophthalmologists and optometrists in private practice offer a full complement of low vision services. Referrals by private physicians are typically made to either State commissions or private agencies.81

National, State, or Private General Rehabilitation Agency

The vision rehabilitation program of the Department of Veterans Affairs is widely regarded as providing the most comprehensive, interdisciplinary array of vision rehabilitation services available in the United States. The VA's Blind Rehabilitation Centers (BRCs) include instruction in visual skills, orientation and mobility, manual skills, ADLs, and communication. The BRCs are inpatient facilities that provide ophthalmologic and optometric care as well as a wide range of medical and nursing care. In addition, psychologists and social workers provide necessary support services and implement family programs, sight-loss discussion groups, and other activities. Candidates for rehabilitation are typically identified by a network of Visual Impairment Service Team (VIST) coordinators who are located throughout the country. One reported drawback to the program is the lack of followup with veterans. It is unclear how long the positive effects of the program last outside of the program.81

Outside of the VA, sources of services include specialty clinics that provide low vision rehabilitation as part of the outpatient services provided by a hospital or rehabilitation facility. State vocational rehabilitation agencies may serve as a referral source to these clinics. In addition, private and State-funded agencies deliver low vision rehabilitation services through a variety of community-based programs.28

State or Private Specialized Vision Rehabilitation Agency

There are more than 30 State commissions for the blind; three-quarters of these offer vision rehabilitation services to eligible individuals. Specific services provided differ from State to State. Ophthalmologists and optometrists may refer patients to State agencies, and the agencies may refer clients to optometrists when an optical device needs to be prescribed. A number of private agencies offer services for low vision rehabilitation. Lighthouse International is notable for the breadth of programs it offers, including low vision clinical services, training in orientation and mobility, adaptive skills training, a device lending system, instruction in the use of new technologies, and counseling.81

Surveys of small samples (n < 100) have shown a variety of results regarding the effectiveness of particular rehabilitation services. These findings are not comparable because both the programs and outcomes measured differ. Geruschat (1993, as cited in Gandy82) found that 81 percent (n = 65) of graduates from a school for the blind went on to college, but generally did not receive competitive wages. Wolffe et al. (1992, as cited in Gandy82) found that some participants in rehabilitation reported receiving inadequate assistance in searching for jobs, identifying career opportunities, and procuring financing for assistive devices. DeLaGarza and Erin (1993, as cited in Gandy82) found that two-thirds of graduates (n = 70) from a school for the blind and visually impaired were unemployed, although subjects reported high levels of satisfaction, independence, and community integration.

Similarly, low vision services administered by a nonprofit vision rehabilitation agency in a metropolitan area were found to have a positive impact on every day function according to the self-report of 133 respondents to a telephone survey.83 In a survey of 149 consumers, Lighthouse International found that almost all (94.1 percent) respondents who received services (i.e., low vision, counseling, rehabilitation teaching, orientation and mobility, technology training, placement services, or career case management) reported satisfaction with services.84 Most reported that the services improved their functioning. However, there were no controls for these data.

There is debate in the field about the relative benefits of services provided by general disability rehabilitation agencies versus agencies specialized in serving the visually impaired. Most studies addressing this debate have serious limitations (e.g., small sample sizes, lack of adequate control groups). However, one retrospective study reviewed data from 36,497 medical records of vocational rehabilitation clients whose cases were closed, comparing those served by general versus separate agencies on multiple demographic, economic, and other outcomes. This study found that specialized agencies served lower socioeconomic status clients, had clients with more severe visual and other disabilities, and had similar or better outcomes compared to general agencies.85

Another study compared services delivered by rehabilitation teachers (n = 507 service recipients) to services delivered by home care managers of Area Agencies on Aging who were trained in vision rehabilitation (n = 85 service recipients). Findings were inconclusive, and no advantages of one type of agency over another were established.86

Community- and Home-Based Services

Community- and home-based rehabilitation eliminates institution-based costs and provides services that are targeted to an individual's specific home environment. Independent living centers are typically community-based, with efforts devoted to environmental adaptations to support independence. Some independent living centers have begun to offer some health care services, and experts predict that this may be a growing trend in the disability field.87 Social Health Maintenance Organizations (HMOs) are managed care entities that integrate health and related services within a single organized delivery system. They were originally developed to address both the acute and long-term medical and social needs of the frail elderly.88 These organizations emphasize provision of long-term care services in the community through a multidisciplinary team.

The home may be a highly appropriate setting for vision rehabilitation programs.89 Rehabilitation services may be more effective when conducted in the environment in which the client will most often function, such as the home.28 Pazell recommends that rehabilitation take a multidisciplinary approach with nurses, occupational therapists, physical therapists, medical social workers, nutritionists, and speech-language pathologists in addition to home care aides.89

Adoption of Services

The adoption of services is affected by a variety of factors, discussed below. The usual financial and physical barriers to rehabilitation are complicated by the fact that a large number of people with low vision, especially older adults, are unaware of available services or are unwilling to seek care.81

Personnel Shortages

There is a shortage of trained vision rehabilitation providers, and few training courses emphasize residual vision and compensatory strategies as significant components in low vision care and vision rehabilitation.56 Methods for addressing personnel shortages include increased reliance on paraprofessionals and peer instructors, and training those outside of the field (e.g., Area Agency on Aging service providers).56 Among existing personnel, knowledge regarding available technologies may be limited; the diversity of professionals involved in rehabilitation makes presents a challenge to professional communication.90

There is also a shortage of researchers conducting work on vision rehabilitation. Clinical and laboratory researchers are generally not trained to conduct research exploring the theoretical framework of vision rehabilitation. In turn, professionals involved in the delivery of rehabilitation services, such as ophthalmologists, optometrists, and special education and vision rehabilitation professionals are not trained to conduct research.

NEI reports that a disproportionate amount of vision impairment research is conducting by researchers trained in experimental psychology. Vision impairment is not a central topic of research for this group of researchers; they are generally not trained in the clinical aspects of vision impairment or in epidemiological or clinical trial research methods.32 NEI has proposed broadening funding awards to those in the fields of special education, rehabilitation, and engineering, and providing researchers with training in vision impairment and rehabilitation and relevant research methodology. NEI also called for vision impairment organizations to foster interaction between vision researchers and the engineers and software developers developing assistive technologies for the visually impaired.

Geographic Access

Geographic access barriers are faced in vision rehabilitation as they are in other health care sectors. In rural or other low-density areas, in which rates of disability are higher, there is frequently only one or a limited range of rehabilitation providers.91 Private agencies that provide comprehensive rehabilitation services are typically located in large urban centers.81 Transportation and proximity to service delivery systems limit access for some individuals, even in urban areas.

Financial Access

Low-income persons suffer disproportionately from vision impairment, and employment rates of the visually impaired are lower than employment rates of other impaired populations.39 Most vision impairment is caused by disease, making access to primary and specialty health care services essential. Of the small proportion (3 to 4 percent) of visual impairments resulting from injury, few are work-related, limiting the role of Workers' Compensation in increasing financial access to care.39

These factors have negative implications for access to expensive technologies. Some States and private agencies have lending systems whereby individuals can try a device before purchasing it to determine if the technology will meet their needs. Some devices are available through State rehabilitation systems, but States are estimated to meet only a small proportion of needs.56,90 In general, program resource availability has not been shown to affect rehabilitation outcomes.

Payment and Delivery System Disincentives

As discussed, vision rehabilitation may include services delivered by a variety of medical and nonmedical providers. Given that vision rehabilitation services have traditionally been provided outside of the medical system by social services or other agencies, the need for vision rehabilitation services may not be perceived as an insurable risk within the medical system. Investment in vision rehabilitation services has not been shown to lead to future cost-savings, as is the case for preventive services that are often covered. In addition, the demand for vision rehabilitation services is potentially elastic. All of these factors may contribute to disincentives for coverage of vision rehabilitation services in health insurance plans.

The Medicare Coverage of Vision Rehabilitation Services Act of 1999 (H.R. 2870) and the Medicare Vision Rehabilitation Services Act of 2001 (H.R. 2484) would extend Medicare coverage to certified vision rehabilitation professionals, including orientation and mobility specialists and rehabilitation teachers. Medicare beneficiaries who are blind or whose low vision cannot be addressed through surgery, medication, or corrective lenses would be eligible. Advocates of the bills cite the coverage as potentially cost-saving to Medicare due to the demonstrated association between low vision and falls leading to hip fractures. The Framingham Eye Study attributed 18 percent of all hip fractures in the elderly to vision impairment.92 The estimated 63,000 hip fractures among the elderly attributed to low vision in 2000 were calculated to result in an estimated $2.2 billion in medical costs. The projected cost-savings of H.R. 2870 and H.R. 2484 is based on the assumption that coverage of vision rehabilitation services would result in reduced vision-attributable falls and hip fractures. There is no evidence that coverage of vision rehabilitation services would be cost-saving.

Awareness of Services

Qualitative research conducted by NEI among individuals with low vision found that there was a lack of awareness of low vision services.93 Moreover, the lack of adequate diagnostic tools may preclude the identification by physicians of a significant number of individuals who might benefit from vision rehabilitation services. In addition, vision loss in the elderly may not be recognized by providers. This phenomenon is illustrated by the low numbers of referrals for vision rehabilitation despite high numbers of patients with AMD.58

Willingness to Utilize Services

The Lighthouse National Survey (1995) found that a majority of those surveyed fear blindness more than other physical impairments.34 Fear may result in delays in seeking care; the underreporting of vision impairments due to the fear of consequences of seeking services was supported by interviews.33 It has been suggested that changing the terminology surrounding vision loss, including referring to "low vision" or "partial sight" as opposed to "blindness" may mitigate some fears.34

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Conclusion

For vision rehabilitation, the research necessary for establishing evidence-based findings of effectiveness is only beginning to emerge. Although numerous studies have measured the outcomes of low vision care, most of these have been longitudinal case series, which are among the less-rigorous study designs for assessing effectiveness. To date, there have been no RCTs that have evaluated the effectiveness or cost-effectiveness of different models of care in low vision. Given the considerable size of the low vision population and the paucity of systematic evaluations, there is a pressing need for evidence about cost-effectiveness in order to inform the design and delivery of services for low vision rehabilitation.

Although some studies do present useful evidence for the effectiveness of selected services, the findings from many of these studies lack external validity, or "generalizability." Diversity in technologies, user populations, and circumstances of use tend to diminish the external validity of findings from studies involving any specific set of these factors. Moreover, while research and publishing in the field are increasing, dissemination of the limited evidence derived from this work has not been effective. In sum, the evidence is characterized by 1) its scarcity, 2) its lower quality, i.e., weaker study designs, and 3) its proximity outside of the general clinical literature, resulting in under-awareness among primary care providers, ophthalmologists, and other clinicians who treat people with low vision.

One of the great challenges to evaluation of technological alternatives for use in low vision concerns the distribution of impairment across the affected population. Although the number of people with vision impairment is high, the variations in the types of impairment and the types of technologies intended for overcoming these impairments are great. As a consequence, there are limited economies of scale in producing and purchasing these technologies. Further, the diversity of technologies and the relatively small numbers of users for whom particular technologies may be effective, limit investigators' ability to design rigorous evaluations of effectiveness with large enough sample sizes to derive statistically significant findings.

The lack of research limits opportunities to establish specific standards of care. The field of vision rehabilitation must build a considerably more substantial evidence base using more experimental designs and other rigorous studies. Aside from establishing whether a service can be effective for one or more indications, it is important to assess the optimum "dosage" of the intervention, e.g., how many times it is provided, with what frequency, and for what hours of service or duration it is provided to achieve desirable outcomes. Consistent with the need to distinguish between "efficacy" (how well a service works under ideal conditions) and "effectiveness" (how well a service works under general or routine conditions), research efforts should seek to evaluate interventions in their routine delivery settings where possible. Economic analyses are needed to track the costs of vision loss, including its direct costs and indirect costs (productivity losses) and the capacity for vision rehabilitation to lower these costs. More work is needed to determine life-long, "downstream" costs of vision loss in younger people. Longitudinal studies are needed to understand at what point the marginal benefits of services subside in relation to the number and costs of these services. As in other types of health care and social services, the greatest improvements from interventions may be gained early, with diminishing returns thereafter.

A related application of longitudinal, population-based studies is to track the impact of vision rehabilitation services not only on visual acuity and functioning, but on preventing or reducing comorbidities throughout life such as preventing falls or reducing the comorbidities of diabetes and other chronic conditions. Clearly, these present clinical and economic benefits that must be included in determining the impact of spending on vision rehabilitation services. Aside from discrete technologies and services used in vision rehabilitation, research is needed to determine the relative effectiveness of referral patterns, delivery settings, and models of care for vision rehabilitation.

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Current as of October 2002
Internet Citation: Chapter 3: Vision Rehabilitation: Care and Benefit Plan Models: Literature Review. October 2002. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/professionals/clinicians-providers/resources/vision/vision3.html