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Ethology and cortical visual impairment

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In industrialised countries there has been a switch in recent decades from ocular to non-ocular causes of visual impairment. The term cortical visual impairment (CVI) is applied to visual loss arising from defects in the geniculostriate pathways although, by default, other neurological defects may be included. The ophthalmological investigation of CVI is difficult and researchers in Utrecht have enlisted help from their local department of ethology (G Porro and colleagues. British Journal of Ophthalmology 1998;82:1231–5. See also editorial, pages 1225–6). [The Greek word ethos is variously translated as character, manners, habits, or behaviour. Ethology is, therefore, the study of behaviour in animals and people.]

 They studied six girls and three boys aged 19–116 months, all of whom had cerebral palsy, lacked visual contact, had no stable visual fixation, and had defied attempts at visual function assessment. Each was observed by an ethologist for 15 minutes, and responses to visual stimuli were observed and recorded on video. As a result of their observations these workers defined six direct signs (indicative of visual perception) and six indirect signs (regarded as supportive or confirmatory). The direct signs were: intermittent fixation towards the stimulus, looking past it, head movement towards it, following, reaching out, and looking away while reaching. The indirect signs were: avoiding behaviour, posture change, smiling, blinking, facial expression change, and sterotypic behaviour.

 More detailed observational studies may improve the understanding of behavioural adaptations to CVI in these children.