Description of the condition
In 2004, the World Health Organization (WHO) reported that more than 161 million people worldwide were visually impaired, with 124 million classified as having low vision and 37 million classified as blind (defined as visual acuity less than 3/60 in the better-seeing eye (World Health Organization 2004). In children, prevalence of blindness varies from 0.3/1000 in high-income countries to over 1.0/1000 in low- and middle-income countries, equating to around 1.4 million blind children worldwide (Gilbert 2001; World Health Organization 2000). Low vision is about twice as common as childhood blindness, and might affect almost 3 million children worldwide (Gilbert 2008a; Gilbert 2008b).
The leading causes of low vision in children worldwide are retinal conditions, corneal scarring (vitamin A deficiency, measles, harmful traditional practices), globe anomalies, cataract, optic nerve anomalies, glaucoma, and central nervous system disorders (Gilbert 2001). A recent study in Nepal identified corneal disease as the leading cause of visual impairment followed by retinal disease and lens pathology. In 46% of children, however, the cause of visual loss could not be identified (Shrestha 2012). In high-income countries, brain damage sustained around the time of birth has become the leading cause of severe visual impairment (Bodeau-Livinec 2007; Mitry 2013; Rahi 2003). In England and Wales, the commonest conditions in children with impaired, but not severely impaired sight, are hereditary retinal conditions or congenital globe abnormalities (Mitry 2013).
In the UK, there are an estimated 25,000 children with vision impairment (VI) or severe vision impairment/blindness (SVI/BL) (Morris 2008). The cumulative incidence of SVI/BL by 16 years of age is 5.9, and that of VI around 7 per 10,000 live births (Bodeau-Livinec 2007; Rahi 2003). About 950 new cases of VI or SVI/BL are diagnosed each year (Bodeau-Livinec 2007).
Children are considered to have 'low vision' when the corrected visual acuity (VA) is between less than 6/18 and light perception in their better eye, or their visual field is less than 10 degrees from the point of fixation, but they use, or are potentially able to use, vision for the planning or execution, or both, of a task (World Health Organization 1992). There is an overlap with the definitions of VI and SVI/BL. The exact definition of childhood blindness is variable, but usually ranges between a best-corrected visual acuity of less than 6/60 to 3/60 in the better-seeing eye in a young person age under the age of 15 years (Gilbert 2001; World Health Organization 2004).
Visual impairment can result in developmental delay by reducing the range of experiences to which the child is exposed. Early assessment with provision and training of low vision aids (LVAs) is essential to improve functional vision and adaptation to visual impairment, so allowing most children to enter and remain in mainstream schools (Ducrey 1998; Massof 1998; Silver 1976a). In the UK, approximately 70% of children with VI are educated in mainstream schools where the use of LVAs to enable use of printed educational materials is essential (Morris 2008). In the developing world, access to enlarged print, or methods to enlarge text (i.e. computers or photocopiers) is more spartan, and magnifiers can be provided as a cheaper and more transportable option for children with low vision. Epidemiological studies in Pakistan have demonstrated that provision of basic magnification aids would permit at least 11% of children currently educated in schools for the blind to be moved to mainstream schooling (Sight Savers International 2003). This estimate, however, was based on a sample of 1000 children in schools for the blind and was subject to selection bias due to the small percentage of children with low vision currently being educated in special schools in low- and middle-income countries; the overall potential for improvement is significantly higher. In Nepal, optical intervention provided a significant improvement to the vision of 48.2% of children in schools for the blind, enabling those learning braille to learn to read visually, or visually in conjunction with braille (Gnyawali 2012). Despite this improvement however, only 34.8% of children were still using their LVA one year later. Damage or loss was the most common reason reported for cessation of use; however, inadequate instruction and inappropriate setting/lighting were also reported, both of which highlight the vital importance of maintenance of equipment - however basic - and instruction to enable its use (Gnyawali 2012).
Description of the intervention
LVAs can be defined as any device that enables a person with low vision to improve visual performance. LVAs can be classified into optical aids (magnifiers) and electronic 'assistive technologies' (AT). Non-optical aids (filters, tinted lenses and coloured overlays) are also sometimes used to enhance vision, but are less frequently used in children with visual impairment and will, therefore, not be included in this review.
Commonly used optical aids include:
magnifiers: hand and stand magnifiers, with and without illumination; in general, the higher the magnification the greater the restriction of visual field
high dioptric power reading glasses or near adds in bifocal glasses (above +4.00 DS and up to +20.00 DS)
distance telescopes or binoculars: a hand-held or spectacle-mounted lens system that provides magnification at greater distance
electronic magnification: the longest established form of electronic magnification uses closed-circuit television (CCTV).
Other devices increasingly used in educational settings include screen-magnifying and screen-reading software operated on computers (desktops, laptops, tablets). For the purpose of this review, we will exclude devices that include monitors to display enlarged text. The present review will focus on optical LVAs; assistive technologies including CCTV will be the topic of a second review. No review is planned on non-optical visual aids.
A different magnification strategy used in educational settings is the enlargement of hardcopy printed material. Decisions about which strategy is superior, i.e. LVAs or text modification, depends on the outcomes selected for evaluation. Any form of visual support, i.e. LVAs or enlarged print, can be expected to facilitate access to the educational curriculum and to enable a child to develop better reading and literacy skills. Compared with text enlargement, LVAs may have the additional advantage of providing children and young people with greater independence of access to printed material (Corn 2002; Douglas 2011). However, peer pressure and the fear of 'standing out' may reduce usage of LVAs by children and young people (Mason 1999).
Why it is important to do this review
Improving functional vision in children with vision impairment is important for enabling education and personal development, and for improving vision-related quality of life. The previously held belief that children with low vision should be treated as children with no vision may in the past have hampered the study and use of LVAs. The WHO identified and highlighted the provision, education and use of LVAs in children as a priority in managing children with vision impairment (World Health Organization 1992).
The use and benefit of LVAs in adults is well documented, although the need for further research into the comparative benefits of different types of visual aids was highlighted by a previous Cochrane review (Margrain 2000; Virgili 2013). Multiple studies document the use and subjective benefit of LVAs in children (de Carvalho 1998; Haddad 2006; Haddad 2009), and training in the use of magnifiers has been shown to improve the beneficial effects of their use (Cox 2009). There appears to be, however, a lack of agreement and comparative data on relevant outcomes and benefits of LVAs in children and young people.
LVA users, i.e. children, their families and carers, as well as healthcare providers or commissioners, require high quality evidence to make informed choices about allocation of personal, institutional and public resources. Facilitating reading and literacy in children and young people not only optimises individuals' access to education and employment, but also benefits society. The rationale for this review is, therefore, to provide critical evaluation of information that is already available from high-quality trials, and to delineate a framework for future research and practice policies in low-income, middle-income, and high-income countries.