Red eyes, blurry vision and stuff like that

‘My eyes have always been fine, but now I have to hold things fruther away to read’.  It’s an oft-repeated line, for people in their early-mid forties, often coming in to have their eyes examined for the first time.

It can come on pretty suddenly for some, this inability to focus up as close as before.  Actually the changes in the eyes that cause the reduced near vision have been happening slowly and constantly for a long time.

The eye focusses for close by changing the shape of the lens inside the eye.  The lenses is surrounded by a circular sphincter muscle, connecting by a series of little fibres.  When the muscle tightens, the tension goes out of the fibres, and the lens ‘relaxes’ to a fatter, stronger shape that gives close focus.  When the muscle relaxes, the tension in the fibres increases, and the lens is pulled to a flatter, weaker shape that gives long distance focus.

Often people imagine that it’s loss of strength in the muscle that causes reduced near vision, but actually the muscles keep good tone throughout life.  It’s the properties of the eye’s lens itself that changes – a young lens is quite flexible, and easily changes shape, and an older lens is stiffer and can’t change as much.  The gradual loss of flexibility means you can’t focus as close as you get older.  Once the eyes are corrected for clear long-distance vision, an average child can happily focus on objects as close as 7 or 8 cm from them; through teens and twenties the limit will be 10 cm or so, in the thirties working its way out to 20cm – but most of that time the change is unnoticed, until it’s suddenly discovered usually in the early-mid forties.

So how come it’s noticed suddenly when the change has been gradual?  30-40cm from the eyes is about as close as most people use regularly, so the loss of clear focus for things nearer than that will usually not be noticed.

The stiffening of the lens process continues, and most people will notice a worsening of their close vision through their forties and into their fifties.  By mid-late fifties, the lenses have lost most of their flexibility.

This is the ‘average’ situation.  Individuals will have different stories, mainly due to how long- or shortsighted they are, or because of difference in strength between the two eyes.