The challenges of research in children with visual impairment

Population studies of infants with visual impairment are rare, as there are challenges in the assessment of vision, identification of the impairment, and the presence of multiple comorbid health and developmental conditions. In the original article by Dale et al., this population was systematically assessed using a large national cohort of 1-year-old infants. This paper highlights several meaningful clinical points. First, children with visual impairment are not all the same. They should be considered in the context of aetiological cause, and comorbid health and developmental conditions. In this study, anterior pathway conditions subdivided this group into simple and complex. This division was based on suspected risk differences of health and developmental conditions. However, it is important to recognize that this division is not absolute. There are many so-called simple conditions that are associated with a range of more complex comorbid conditions. As a result, grouping children with visual impairment is a difficult process. Second, the criteria for visual impairment are based on the International Classification of Diseases, Tenth Revision (ICD-10). It is not clear whether these criteria should be applied in infants. In many cases, infants may not meet criteria for a visual impairment in adulthood, such as ocular albinism or cataracts. Alternatively, some children initially appear to have appropriate vision, only to later develop a visual loss. Given that visual acuity in childhood can change over time, the categorization of visual impairment and its severity in infancy should be considered dynamic. In addition, the progress of vision may not always follow a similar course amongst differing conditions. So, there is no standard definition of visual impairment and severity in infancy. Third, visual acuity is a developmental/behavioural assessment which has been standardized through matching symbols at a distance. In this series, estimations of visual acuity were based on the Near Detection Scale, an assessment which requires a certain level of skill. For those clinicians less familiar with the assessment, measures of acuity are influenced by many factors. One such factor is visual attention, which is more difficult in infancy and in the presence of developmental disability. Visual attention is also influenced by other factors, including environment (e.g. lighting), health (e.g. seizures), and developmental conditions (e.g. motor impairment). All these elements contribute to make the assessment of visual acuity more challenging. Fourth, many anterior pathway conditions may be associated with posterior pathway components of visual impairment, particularly optic nerve and structural eye conditions. These conditions are often associated with complicated health and developmental issues. Grouping some of these conditions together without first identifying the presence or absence of other possible causes of visual impairment may be problematic. Finally, the developmental assessment of children with visual impairment is difficult. The Reynell–Zinkin Scale, commonly used in the assessment, lacks psychometric standardization. Current medical conditions and diagnostic tests are of course quite different from the late 1970s, when the Reynell–Zinkin Scale was first developed. Since then, there have been better diagnostic tests and detection of vision conditions. This means that the patient population under study today may not entirely represent the same population assessed during the development of the tool. Despite this, this paper by Dale et al. clearly demonstrates that limitations in vision have an impact on development, with those with more complex aetiological conditions and/or greater severity having greater developmental consequences. This present paper presents a relatively homogenous group of peripheral vision conditions. It is a good attempt to create a better understanding of this population’s differences. Clinicians should be aware that the larger more heterogenous group of children with visual impairment (the population not studied) are associated with greater comorbid health and developmental conditions.