JOURNAL WATCH

NEW HOPE
The long-held dogma that deprivation of vision during critical periods of childhood development results in irreversible vision loss is called into question by a recent US study. In a study of a group of paediatric patients in India who were blind during the critical childhood period before removal of bilateral cataracts, Peter Bex and colleagues at Harvard University found improvement in contrast sensitivity tests after vision returned. Some of the patients were as old as 15 years. “Our results show remarkable plasticity, and vision continues to improve in many children long after the surgery,” said Dr Bex.

The findings call into question the concept that there is a critical period of a few years during which the visual system can develop. The research was conducted on patients in India under the auspices of Project Prakash a joint scientific and humanitarian effort led by Pawan Sinha PhD, full professor at MIT. The project addresses the problems of treatable blindness in India by providing surgeries free of cost to children with cataracts. Unlike patients in the western world, Indian children with cataracts are not usually treated within the first year of life.

The research parallels changing attitudes towards the treatment of amblyopia, where the window of opportunity, once though to be limited to the first few years of life, has been expanded to the later teen years. These findings of neural plasticity in visual development have further implications for many areas of ophthalmology.

A Kalia et al., PNAS, “Development of pattern vision following early and extended blindness,” 2014 111 (5) 2035-2039.

EXERCISE
Moderate aerobic exercise could help to slow the progression of retinal degenerative disease, a new study hints. In an animal study US scientists trained wildtype BALB/c mice to run on a treadmill for one hour per day, five days per week, for two weeks. They then induced retinal degeneration with toxic bright light and exercised the animals for another two weeks. The exercised animals lost only half the number of photoreceptor cells as control animals.

Moreover, the retinal cells of exercised mice were more responsive to light and had 20 per cent higher levels of the growthand health-promoting protein brain-derived neurotrophic factor (BDNF). After blocking the receptors for BDNF with systemic injections of a BDNF tropomyosin-receptor-kinase (TrkB) receptor antagonist reduced retinal function and photoreceptor nuclei counts to levels seen in inactive mice.

Previous studies in animals and humans indicate protective effects of exercise in neurodegenerative diseases or injury, but less is known about how exercise affects vision. “This is the first report of simple exercise having a direct effect on retinal health and vision,” said Machelle Pardue PhD, one of the study authors.

EC Lawson et al., Journal of Neuroscience, “Aerobic exercise protects retinal function and structure from light-induced retinal degeneration,” 12 February 2014, 34(7): 2406-2412; doi: 10.1523/JNEUROSCI.2062-13.2014.