Science World Blog Can You Read This?
Can You Read This?
Last Updated (Wednesday, 23 September 2009 10:08) Written by Raymond Nakamura
The Eyes Have Had It
Lately, I've noticed it's easier to read if I take my glasses off. So I went to get my eyes checked and my optometrist told me I have presbyopia, which means "old eyes." That's what some people need reading glasses for.
Seeing the Light
The cornea at the front of the eye not only protects the insides but does most of the heavy bending of light. The lens is important for sharp focus. It can let light through because it's made of cells that contain special proteins and not much else. These cells and even the proteins in them don't change over time. The ones we were born with are still there.
Looking Your Age
That's why you can tell when someone was born by the amount of the carbon 14 isotope in the lens. The freaky thing is the spike in the atmospheric levels of carbon 14 after Hydrogen bomb testing in the 50s and 60s.
Let's Shift Focus
Anyway, before you start falling apart, your eyes can change focus. The little muscles around the edge of the lens pull or relax so the shape of the lens changes. With presbyopia, your lenses don't adjust as well any more. The question is, why does this happen?
A Stiff Wink
The classic and long-standing explanation for presbyopia has been that the lens becomes stiffer as you age, so it doesn't adjust so easily. This comes from the work of a very smart guy named Hermann von Helmholtz, a German scientist during the 1800s, who not only did important work in physiology but also mathematics and physics.
Not Seeing Eye to Eye
Recently, Ronald Schachar has advocated a different theory, with much controversy. He says that the lens continues to add cells around the perimeter. This means the muscles attached to it lose the amount of play they have, limiting how much the lens can change thickness and the amount of focus.
Two things make me a little skeptical of this new explanation. One is that he named it after himself (the Schachar theory) and two, he is claiming that presbyopia could be fixed by surgery, which he performs (cha-ching).
In Theory
But that is just mud-slinging. I love that a 150-year-old widely accepted idea is being tested. That's what we always say science is all about. My optometrist seems to support the Schachar theory, although she wasn't trying to sell me on surgery. Schachar has made distinctive, testable predictions about the properties of the lens. But the data are still being gathered, so we'll just have to wait and see.
