Astigmatism and Presbyopia

Astigmatism explained

Astigmatism is the word we use to describe the condition where the front surface of the eye, (the cornea), or the lens inside the eye, is irregular in shape. This result in blurred vision at all distances, however it is not a disease, but is actually a very common condition. In fact most people who are long or short sighted have some degree of astigmatism. Small amounts cause no problems, but moderate to high astigmatism will need to be corrected. It is actually so common, that unless it is quite severe, you may not even be aware of this component of your overall prescription..

This irregularity often likened to a rugby ball shape, means that not all the light will be brought to a single point of focus inside your eye. In fact the focus will be spread out.
The cause of the irregularity is not known for certain, but it may be hereditary, or caused by the pressure of our lids or the tension of the muscles, which control eye movement. People who are astigmatic usually experience a small increase in their astigmatism over the years; however, it can be easily corrected using spectacles as well as contact lenses.

The lenses used to correct astigmatism are called, toric. These lenses are manufactured with complex curves on the surfaces; these compensate for the irregular shape of the eyes, and bring all the light to a single point of focus. When this point focus is brought onto the retina, we achieve our best possible vision.

Presbyopia explained

Presbyopia describes the completely normal condition that comes to us all with age, when we find it more difficult to focus on object that are close.
It is caused by the reduced flexibility of the lens inside the eye.

Even if we have perfect vision in the distance we will all find close work more difficult later in life.
When we are young, this little lens has the ability to increase the focusing power of our eye by up to ten units. As the total power of the eye is around sixty units, this extra ten means that we can hold things very close to our eyes and still keep everything in focus. In fact as we only need about three extra units of power to focus at our normal reading distance, having this extra ten means that we always have plenty in reserve. However, from the age of about twenty, this lens begins to harden and we progressively lose the extra power. This progression is very predictable, and usually by our early fifties we are beginning to find that our arms are not long enough any more. Having to hold things so far away to have them in focus that they are now so small that we cant see them well enough.

Having lost our natural ability to increase the eye’s power we now have to replace it with reading glasses. As the loss of extra power is progressive, we find that over the years we gradually have to increase the strength of our reading glasses to compensate. It is quite normal to begin with a power of about plus one unit and to increase to plus three when we no longer have any flexibility remaining in the natural lens. This process normally takes place between the ages of forty-five and sixty.
If you are beginning to hold things slightly further away to get them in focus, then you are becoming presbyiopic. Constantly doing this is quite stressful and may easily lead to headaches, tiredness and the feeling that you have to keep reading things several times before they sink in. You don’t need to put up with this as it is very easily corrected with reading glasses often producing quite dramatic improvements in vision and comfort.
Will we all eventually need extra help for reading? Unfortunately the answer is yes. The only people who get away with it are those who are short sighted. Because their eyes are naturally too strong, they can use this extra power for close up by removing their spectacles. For the rest of us, bifocals, multifocals, varifocals or reading glasses are a natural progression. Now it is possible to correct presbyopia with either spectacles or contact lenses without any problem.

Paul Graves
Body’s Opticians