Friday, 24 July 2015

The eyes have it

Dopamine! Or rather they don't . . . any more. One of the remarkable things about evolution is how we grow up symmetrical.  Our arms grow to the same length! That's an amazing fact that should be a source of wonder but is effectively invisible until someone buggers it up. Thalidomide anyone?  If it's so obvious to all thinking people, how would you make-it-so that the amount of growth hormone is perceived as precisely the same at two places as far from each other as it is possible to be while still attached to the same circulatory system? Here's another growth and development conundrum - how did your two eyeballs grow from tiny dreamy infant eyes to far-seeing adults eyes and all through that time maintain a focal length correct for the lens in front?  It's the dopamine stupid!  Dopamine is one of 100 [!] known neurotransmitters but here, like other NTs adrenalin and noradrenalin, it acts as a (growth) hormone.

I was up in Dublin yesterday and picked up a handful of oldish Science and Nature magazines from the coffee room.  Several of them still in their plastic mail-wrappers.  I'm glad I'm not the only one who pays for a subscription and then doesn't get round to reading the latest stuff from the two premier general science journals. In between drooly dozes on the way home on the bus, I was leafing through the easy-to-read parts when I was brought up all standing with a WFT statistic . . .

96.5% of Korean 19 y.o men are short-sighted! And those stats are echoed in most other countries.  In two generations, the proportion of myopic Chinese teens has gone from 10% to 90%.  Elie Dolgin has written a gob-dropping essay about the cause and effect of the myopia [L] epidemic in 19/Mar/15 Nature called The Myopia Boom.  That's 4 months ago and the story has already sunk beneath the woefully short attention span of the media. We know and worry about the obesity epidemic - Ireland's teens are fatter than the EU average and the country is scheduled to top the European obesity rates at 86% of adults by 2030.  We're not doing much more than wringing our hands over that, but I haven't heard anything about the rise and rise of myopia. Although, of course, I have noticed that opticians are occupying a lot of prime retail space in our city-centres. It could be that there is a very simple solution to both problems - get the kids outdoors every day.

It gets back to how you would force the eyeball to grow at a rate precisely correct so that light can focus on the retina. You use the light . . . to stimulate the production of dopamine in the cells under the retina; this light-induced blat of dopamine prevents the elongation of the eyeball which is the physical cause of myopic unfocus.  You also have a complex system of muscular responses to give your eye some "accommodation": so long as dopamine gets the retina more-or-less the same distance the iris can tweak the lens to precisely focus the incommming. This accommodation is what is failing in my aged eyes over the last year forcing me to take on two sorts of glasses.  That's the sort of absurd kludge that evolution delivers - and it works fine for people who spend every day out on the Serengeti gathering berries, hunting down an occasional pig and sitting in the shade telling stories and flirting.

But it's not candle-light!  Even a 100W electric light bulb is nowhere near sufficient to induce the photochemical reaction. One of the many things I learned from Mr Wilkinson, my high-school biology teacher, is that we perceive light on a logarithmic scale and he showed us how this works by taking a light meter on a field trip to the bluebell woods at Blean.  Our subjective impression of  double the light intensity was actually 10x in terms of photons, foot-candles, talbots, candelas, lumens or lux.  A well-lit classroom might shine 500 lux on page or key-board and we're fine with that for learning the names of the Presidents of the Republic and making Lara Croft do our bidding but children need 10,000 lux for 3 hours a day to keep them out of Specsavers until they are middle aged. They don't have to do anything out there - they can read a book - but of course being out in the fresh air makes it easier to get some exercise that will fight off the flab. Obviously the solution is more complex than that.  You'd rather your kids contracted to buy spectacles than contracted melanoma but ignoring these data is not part of a solution.  Ministers of Education, Children, Health please note . . . and do something about it.

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