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Measuring impairments

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By now, you are familiar with the international classification, a functioning disability and health. A biopsychosocial model of disability. In this step, we will focus on body functions and structure and how impairments in the body function and structure can be measured. We will focus on impairments as described in Article I of the CRPD– physical, mental, intellectual, and sensory impairments, which means impairments in vision or hearing. It is important to recognise that the impairments are not a proxy for disability. As we’ve seen, information on impairment alone does not capture the impact of the impairment or not on how the individual functions in his or her environment or the degree that she or he can participate in society.
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With that said, understanding the type and causes of impairments that people have can help in designing and implementing services that meet their needs. For example, consider a child who has difficulty seeing. This may be because they have a paediatric cataract, which is easily operable and can fully restore their sight. Or it may be because of a neurodevelopmental health condition, such a cerebral palsy, in which the communication between the child’s eyes and brain is disrupted. No medical interventions can restore sight in this instance. But the child’s independence can be supported through inclusive education and assistive devices.
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Collecting population-based data on vision impairment can help us plan based on the need for cataract programmes, child vision screening programmes, inclusive education programmes, and assistive technology programmes. This information is particularly useful at the population level. For example, in surveys so that the population need can be determined. As you can see from this example, understanding the cause and the type of impairments can be useful in designing services beyond health services. Education, work, social inclusion, rehabilitation, and water and sanitation are all examples of areas where designing programmes and policies to support people with different types of impairments is important. There are number of recognised methodologies for measuring impairments in disability research.
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And in particular, in population-based research such as surveys, many have been validated, meaning that they have been formally tested and found to measure the intended outcome well. Generally, these tend to include an objective impairment screen that can be completed by a trained but non-clinical person, followed by an examination of people identified to have impairments by relevant clinician. Because of the need to include clinicians in the field, as well as expensive and historically cumbersome specialist clinical equipment, population-based impairment studies are relatively expensive. In recent years, however, a number of new mobile-based tools and methodologies have been developed, which increase the feasibility of measuring impairments, which we shall review now.
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The World Health Organisation has developed standard definitions for vision and hearing impairment. Vision impairment is defined based on presenting distance visual acuity in the better eye, which can be measured using a vision chart. There are several validated ways to do this, including a number of smartphone-based apps. The rapid assessment of avoidable blindness is the most common vision impairment survey methodology worldwide, and now, integrates vision screening on a mobile phone using peak acuity. Over 300 RAABs have been completed worldwide. RAAB only examines the population 50 plus, where the prevalence of blindness is high. So the sample size, and therefore the survey cost, is low.
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Data from this group can be used to estimate the all age prevalence without requiring a large all-age sample.
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Clinicians, usually ophthalmologists, are required to examine eyes in vision impairment surveys. This is so they can establish the cause of vision loss and, therefore, the population eye health needs. Equipment ranges from relatively simple to complex, depending on the detail of the examination. In RAAB, only a direct ophthalmoscope is required. The data are collected using a mobile phone. A number of organisations are also working on the use of artificial intelligence to grade ocular photos, which in future may replace the need for both clinicians and equipment other than cameras. Similarly, the World Health Organisation definition of hearing impairment is based on hearing acuity in the better ear.
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Also, similarly to vision, the rapid assessment of hearing loss, which was recently developed at ICED, uses a validated smartphone-based hearing acuity app called Hear Test to measure hearing in people 50 and above. Other apps exist, such as Shoebox, which can also be integrated into surveys. Clinicians at EMT nurse level or equivalent are required for the ear examination, although again, artificial intelligence and video otoscopy are currently being investigated as alternatives. Physical impairments may be caused by a vast range of different health conditions and different life stages or through trauma. A number of tools exist to measure physical impairments directly related to a specific health condition. For example, impairment related to clubfoot.
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Fewer tools exist to measure physical impairment more broadly, with case definitions of physical impairments not well-defined, making it more complex to measure them than sensory impairments. One tool is the Rapid Assessment of Musculoskeletal Impairment, also developed at ICED. The RAM is a two-stage tool, including seven screening questions asking participants about difficulties with functioning. Participants who screen positive undergo observation of activities in a standardised examination with case definitions by a physiotherapist or other clinician. No equipment is needed. RAM was first validated in Rwanda, and has since been used in surveys of musculoskeletal impairment in India, Cameroon, and Turkey.
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As with physical impairments, there are a number of condition-specific tools that have been developed for mental health screening, particularly in high income health facility settings. However, relatively few have been validated for use in the population in general, and in low middle income countries in particular. The two most commonly used in surveys and LMICs to date are the PHQ-9, a nine-item depression screening tool, and the GAD-7, a similar tool for generalised anxiety disorder. Any use of these tools requires careful translation and pilot testing of items to make sure that they are locally relevant and that the scoring criteria is appropriate to the local population before they are used.
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Because they are question-based, mental health impairment tools do not require specialist personnel or equipment and can be delivered using a mobile device. However, because they collect data which might be sensitive, data collectors must be well-trained to deliver them. The measurement tools available for intellectual impairment also tend to be high income and condition-specific, such as tools for dementia. Few tools have been validated in LMIC. And an additional difficulty with measuring intellectual impairments is that the cause of intellectual impairments can be difficult to identify, even in clinical settings and following complex diagnostic evaluation. So in summary, impairments are a component of disability.
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There are different tools available to measure impairments at the population level, which can be useful for planning and implementing a wide range of services that support people with disabilities. Clinicians are required to examine participants and identify the cause of impairments. And specialist equipment may be required, which can add to the cost of research. However, mobile screening tools are available for several impairment measures, with AI examination of photographs in development for some impairment types. In addition, impairment survey methodologies have been developed that examined subgroups of the population where prevalence is higher, and, therefore, sample size and associated costs can be lower.

In this step, Dr Islay Mactaggart will introduce how we can measure impairments that cause disability. The step focusses on measurement of impairments as described in Article 1 of the United Nations Convention on the Rights of Persons with Disabilities: physical, mental, intellectual and sensory impairments (which means impairments in vision or hearing).

Dr. Mactaggart is an Assistant Professor in Disability and Global Health at the International Centre for Evidence in Disability and the International Centre for Eye Health at LSHTM.

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