Masters of Health Magazine September 2018 - Page 19

Research published by the Brien Holden Vision Research Institute at the University of New South Wales, Australia in 2016, revealed the alarming statistic that over the past thirty or so years, myopia has increased 300 percent, sometimes more, in both developed and developing nations. At current rates, by 2050, half the world’s population will be myopic. Of these, 10% will suffer from high myopia (>-5.00 Dioptres) which places them at risk of ocular morbidity (loss of vision) in later years of life. This occurs because of a myopic form of macular degeneration, glaucoma, retinal detachment and cataract at an early age.

For some years the shared view amongst researchers was the increased reading and computer time to which school, university students and office workers were subject was the central reason for this increased frequency of myopia on a global scale.

Many researchers overlooked the background exposure to ambient light experienced by the subjects of their research. They also commonly relied on questionnaires for both subjects and sometimes for children or their parents, which may not always be an accurate history of reading/study and time spent outdoors. Often in comparing cohorts, the crucial variable of ambient light exposure was not accounted for. Indeed, parental myopia and near work were typically targeted by researchers as the most likely contributory factors which explained the variable results found in the literature.

A publication by Mountjoy in the British Journal of Medicine in June 2018 has clarified this view. Using a large DNA database of more than 67,000 subjects and sophisticated DNA statistical analysis (Mendelian randomisation) and combined with a questionnaire, he and his team confirmed that time spent in education has a very positive association with myopia, not genes.

Two Australian researchers, Prof. Kathryn Rose and Prof. Ian Morgan showed that in comparing Chinese school children aged 7 years in Sydney with those of the same age and ethnicity in Singapore, the incidence of myopia was ~10X more in those children in Singapore where they were exposed to 75% less sunlight on average per week. The question raised was: “what is the essence within sunlight that provided this benefit”?

Preservation of the circadian rhythm and the pupillary light reflex in certain eye pathologies made researchers long consider the existence of a mechanism that contributed to our circadian rhythm and pupillary light reflex quite apart from the rods and cones that provided the initial response to light within the retina so contributing to vision. In 1995 Czeisler et al published their findings on the preservation of a normal circadian rhythm in a number of subjects without light perception. This suggested a retinal system sensitive to light but not projecting to the visual cortex but to an area within the mid-brain controlling the release of melatonin, the supra-chiasmic nucleus (SCN).

It was research by Foster et al in 1999 who confirmed it was not the rods and cones responsible for setting the circadian clock but an altogether separate system still capable of responding to light and communicating with the mid-brain for circadian control.

The ipRGCs were later identified by Bergsen et al in 2002 and noting prior research by Provencio et al in 1998 who identified the presence of melanopsin, a unique retinal ‘opsin’ unique to the ipRGCs (but common in its molecular structure across nocturnal rodents and diurnal primates) as the photo-pigment within ipRGC’s.

Myopia: The growing global incidence and

the role of light