Common Eye Conditions

Presbyopia

This term is used to describe what happens in the eyes when they get a little older.
Normally first noticed around the mid-forties. To see things clearly near to we have to increase the power of the eye, the closer the object the more of an increase in power is needed.

To achieve this increase we distort the lens in the eye, the greater the power the greater the distortion needed.

The lens is made up of a series of layers and as we get older the thickness of the lens increases in much the same way as a tree trunk goes thicker as it ages. When either of these structures thicken they become harder to bend.
You can bend a sapling quite easily but a few years later it resists bending more and a few years later you can’t bend it at all despite being just as strong. The same problem occurs with the eye as we age, when we want to bend the lens (we call it accommodating) even though we still exert as much force with our muscles we get a lot less of a change in the shape of the lens as it thickens and so less of a power change.

The result of this is that we start holding books etc further away to make it so we don’t need as much power but then the print starts to become too small or our arms aren’t long enough. Even with this adaptation the eyes are working at their maximum and after a short while feel uncomfortable, lose focus and possibly give headaches. This is the time that reading glasses are needed.

The correct prescription will give the least help necessary to make the work needed by the eye comfortable, still leaving the eye to make up the rest and keeping tone in the muscle. Unfortunately as the eye gets older
the lens will become thicker and less pliable meaning a greater dependence on the spectacles.

Hopefully this shows that the cause of the problem is not that the power in the muscles has deteriorated, rather that the same amount of force exerted on the lens will no longer create the distortion it once did.