The literature on nearwork-induced transient myopia (NITM) is reviewed, with NITM being defined as the short-term myopic far point shift immediately following a sustained near visual task. A majority of these investigations demonstrated the presence of NITM for a variety of test parameters, e.g., visual acuity, contrast sensitivity and far point. Overall, these studies reported relatively small myopic shifts, with a mean of approximately 0.40 D and a range from 0.12 to 1.30 D. The subsequent decay is characterized by an exponential function with a relatively short time course. While the precise etiology and implications of NITM remain unclear, speculations regarding its origin and relevance to clinical myopia are discussed. Studies that did not demonstrate NITM are also reviewed.

range of nursery-lighting conditions is remarkably uniform. The association we find between parental myopia and nursery night-time lighting suggests that Quinn et al.'s study should have controlled for parental myopia.Another possible difference is that Quinn et al.'s sample is not representative of juvenile myopes. It was drawn from a tertiary referral, paediatric ophthalmology outpatient clinic, and the sample had a median age of eight (young for a sample of myopes) with a very high proportion of myopia (30%). Our sample had fewer myopes and fewer hyperopes, and the children were older. Also, the proportion of parents reporting that their infants slept under full lighting is different in our study: more than 15% of their clinic-based sample had full nursery lighting, whereas only 3.7% of our representative, school-based sample had full room lighting at night.Our results indicate that myopia is unlikely to develop in children as a result of exposure to night-time lighting as infants. brief communications 144 NATURE | VOL 404 | 9 MARCH 2000 | www.nature.com

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