Monocular amblyopia occurs in at least 1% of individuals worldwide, causing decreased visual acuity as a result of abnormal early visual experience. Screening for amblyopia in early childhood is done in many countries to ensure that affected children are detected and treated within the critical period (in early childhood), and also achieve a level of vision in their lazy eye that would be useful should they lose vision in their other eye later in life. However, considerable international debate surrounds the value of screening for amblyopia. Jugnoo Rahi and colleagues from the Institute for Child Health, London, UK, aimed to investigate the risk, causes, and outcomes of visual impairment attributable to loss of vision in the non-amblyopic eye among people who had monocular amblyopia.
National surveillance was done to identify all individuals in the UK with poor vision in their lazy eye, and who had newly acquired visual loss in the non-amblyopic eye. Of 370 eligible individuals (age range 1-95 years), 28% had socially significant visual loss, 49% had visual impairment, and 23% severe visual impairment or blindness, according to World Health Organisation criteria. The minimum risk of permanent visual impairment by age 95 years was 33 per 100 000 total population. The projected lifetime risk of vision loss for an individual with amblyopia was at least 1.2%. Only 35% of people previously in paid employment were able to continue work.
Jugnoo Rahi comments: "In addition to any direct benefits of improved visual function in the amblyopic eye per se, effective treatment of amblyopia during childhood--to achieve a good level of functional vision in the amblyopic eye--remains a potentially valuable strategy against incapacitating vision loss later in life. Our findings serve to emphasise an important potential benefit of detection and treatment of children with amblyopia, which has been underestimated previously."
In a research letter in this week's issue of THE LANCET (p 621), from the same study, the investigators report the chance of visual improvement in the amblyopic eye following loss of vision in the non-amblyopic eye and the factors associated with this. Of 254 individuals in the study who were visually mature (aged 11 years or more), 10% had improved visual acuity in their amblyopic eye at one year follow-up. The investigators suggest that this supports the notion of some plasticity in the visual system of a few visually mature individuals with amblyopia, warranting further study. However they stress that children should remain the priority for detection and treatment of amblyopia.
Stephen Cox, Press Office, Institute of Child Health,
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