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A PHYSICIST WRITES . . .
(October 2006)
It was back in March 2004 that I last wrote about the eyes and the brain. I said that your subconscious brain regards many of the details captured by your eyes as unimportant, and so it’s rubbing them out all the time, before you can consciously ‘see’ them. Otherwise, the brain would be overloaded with them beyond endurance! Also, it cleverly fills in some of the gaps in your view of the scene ahead. For example, everyone has a blind spot in each eye: in your left eye it’s just to the left of where you’re looking, and in your right it’s to the right. But you never notice these gaps normally, because your brain covers them up.
I was reminded of all this when eyesight was in the news last month. In a survey of 3000 drivers, 15% said they had problems in reading road signs. For drivers in their 20s the figure was 30%. And these were free confessions, not the results of roadside eye-tests — so what’s the actual proportion of people, I wondered, driving around with uncorrected eye defects? Then came a warning from the RNIB that various eye diseases leading to blindness can be triggered by obesity (not to mention smoking). Their message to the overweight is Lose Some. The message to everyone: get regular check-ups from an optician.
The fact is that eyesight, like hearing and the sense of smell, can deteriorate quite a bit before you realize something is wrong. You become accustomed to the picture your eyes give you, and you assume this is as good as it gets. At the age of 5, I couldn’t read the blackboard from the back of the class-room, but I thought this was normal. Then I was fitted for specs, and I can still remember my amazement at being able to see individual leaves on distant trees! So I can quite believe that many drivers gradually go shortsighted, for instance (not as much as I am, but enough to be a danger on the road), without realizing the seriousness of it or doing anything about it. And if the text on road signs is escaping them, what other vital information are they overlooking?
There’s another (partial) explanation for the results of the survey. As I said, the brain prioritizes the information the eyes take in, with the result that you may literally only see those things that you are looking at — or looking for — while other items fail to register with you consciously. If a less experienced driver is in the habit of concentrating on the road itself in order to steer a straight path, it’s quite possible that a road sign won’t be noticed until it’s too late for it to be read. So train yourself to look from side to side all the time, as well as ahead.
Thinking now of actual diseases of the eye: my late father was not obese (nor a smoker in later life), but he did get glaucoma. This was detected in time for its progress to be halted, luckily. He was still driving in his late 80s. What finally stopped him was a kerb on a dual-carriageway in the dark: he swung too sharply into a right turn and missed the exit road (though he knew the junction well). His car then stopped another one and was a write-off. By great good fortune, only bruises were suffered.
A week later the officer in charge of the case paid a visit, and I made sure I was there too. Came the crunch question: “I’ve got to tell you that we’re looking at the possibility of charges ... unless you’re willing to give me your driving licence?” My father turned to me for reassurance. I nodded, he said yes, and all was well. I asked the cop, as he left, why he had parked some distance down the road: “Just in case I needed to do an eyesight test on my number plate.” Anyway, my parents soon adapted to taking taxis (saving some money) — and my mother at 98 keeps the taxi firm in regular business still!
But I digress. I knew that the risk of glaucoma can be hereditary, so I’ve long been having special checks for it at the optician’s and at hospital. Then last June it was detected from a ‘fields’ test, which finds any unresponsive areas on the retina. My left eye showed several small patches, my right eye none I think (apart from the regular blind spot). But because the diagnosis was glaucoma in both eyes, I was legally obliged to notify the Medical Group at DVLA.
The eye-drops that I now apply every night should stop the glaucoma in its tracks, but they can’t reverse the effects it’s already had. And I must stress that in normal looking around, these patches are as invisible to me as the ordinary blind spot is, because the brain is so good at covering them up. This is the insidious feature of glaucoma and several other eye diseases: you simply don’t know they are developing, until (I guess) you finally do realize that you can’t see in some directions. But by then you will be in real trouble — very likely to lose your driving licence and possibly your sight.
That’s why regular eye-tests can be vital. The optician may well decide there’s no need for a proper fields test, but I’ve found a way of doing one on yourself. Fix a smallish black object to a light-coloured area of wall, sit back comfortably, cover one eye, and with the other sweep your gaze slowly over the whole wall. If all’s well, you should be able to see the object all the time, except of course when it finds the blind spot (check the top of this column for the location). Good luck.
Peter Soul
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