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Hi Guys As an optometrist I feel I have to comment
on a few urban myths that have crept into an otherwise very accurate
discussion. WRT Depth of field; The eye has a clever mechanism called the
accommodation reflex. If you look at a close object the lens of the eye is
adjusted to improve the focus, and at the same time the eyes converge (so that
you don’t get double vision) and the pupil constricts. The eye does this
to improve the depth of field and to improve the focus. This reflex is hard
wired into the brain. It still occurs in people using a bifocal. WRT Pterigium The risk factors are; Dust, Dryness, and
UV light. So wear a hat, and sunglasses and if you get dust in your eye rinse
it out. I do not recall seeing anything suggesting that eye colour is a risk factor.
If you blue eyed people want something to worry about you should worry about
Age Related Macular Degeneration (especially if you smoke). WRT Astigmatism I have not found it to increase with age.
However it may appear so. The brain is very good at resolving blur,
particularly the brains of younger people. A 15 year old with astigmatism may
not perceive blur. However a 45 year old may notice the blur and prefer to use
a correction. But the underlying amount of astigmatism hasn’t changed. WRT Infinity We are taught that as far as the eye is
concerned anything beyond 6m is at infinity. (Of course there is a theoretical
difference between 6m and infinity, but in practice it is not significant.)
That’s why all of the testing is done at 3m, with a mirror to double the
distance. It is certainly worth telling your optometrist that you need good
vision at infinity to make sure you get the best lens possible. There is a
certain amount of art and judgement to prescribing which is not always
apparent. Given more information your optometrist is more likely to give you a
lens you are happy with. One point not raised, is that for the 7%
of males who are colour blind, a brown or tan tint can often be an advantage. Finally tints are very personal. What
works for one person may not work for someone else. It really is trial and
error. The same is true of bifocals or progressive lenses. Mandy ( BSc MBCO |
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