At some stage, everyone starts to have trouble reading fine print. Whether the page is moved close to the eyes or held at arm’s length, the print is blurred and attempts to read it are frustrated.
This loss of near vision happens to all of us and is quite normal. It begins for most of us in the early forties and this is called presbyopia. Fortunately there is a solution to this problem, wearing corrective spectacle lenses brings the sharpness again to fine print.
How your eyes work
Light rays enter through the pupil and are bent by the lens inside the eye so that they come to focus on the retina. The image formed is transmitted to the visual centers of the brain via the optic nerve.
The lens of the eye is responsible for about 30 per cent of the eye’s total focusing power. As we age the lens becomes less flexible until it eventually loses the ability to take on the deeply curved shape required to focus on near objects.
Young eyes adjust easily
When we are young the lens inside the eye is quite flexible. This allows the lens to change shape to refocus the light onto the retina for near objects.
Near objects blur in presbyopia
When the lens is no longer as flexible it will no longer bend light rays enough, therefore images formed on the retina by rays from near objects become blurred. This is because they are now focused at a point beyond the retina. The brain receives an image no clearer than that which the retina sends. A focusing aid is needed.
Bifocal lenses in early presbyopia
With the aid of bifocal lenses, the eye can receive a sharp picture for distance and near. For a few years the lens of the eye retains sufficient flexibility to allow an overlap at intermediate distances. Vision at this range is good while looking through either part of the bifocal lens.
Growing gap between near and far vision
As the focusing ability of the lens decreases further, we encounter a gap between the point where sharp near vision leaves ends and sharp distance vision begins. This is called the intermediate range around arm’s length and a little further. It is hardly noticeable at first but becomes wider and more disturbing with time.
Trifocal segment restores vision
A three-way or trifocal lens brings back keen vision in this range. It contains an additional segment, which bends light rays properly for things seen at arm’s length-objects on a tabletop, the instrument panel of your car or a computer keyboard. A clear, unbroken range of vision is restored.
Progressive lenses are often recommended. These lenses do not have definite dividing lines between the different portions of the lens. The wearer has an infinite number of focusing distances. All distances are sharp and clear.
Advice on vision care
As your ability to focus declines you will need to have your eyes checked and your prescription changed every few years. Changes in vision due to presbyopia may continue to occur until around the age of 65 years.
Often factors other than age and visual conditions influence seeing problems. Certain visual tasks in our daily occupation may require specially designed lenses. Discuss your visual activities with your optometrist to ensure that you attain your full visual potential.
Apart from checking on the continuing condition of presbyopia, the eyes of people aged 40 years or more should be examined every two years to exclude the development of other eye health problems.