There are quite a few ways that eyes can get out of focus. Glasses or contact lenses are used to restore clear, comfortable vision, by adjusting the focus of the eyes. Lenses can be made that just correct one type of blur, or they may be correcting the vision in multiple ways.
Myopia - Short-sightedness
A myopic eye is one that is not clearly focussed for things further away. It is usually because the eyeball has grown too long, or because the lenses in the eye are over-strong. Myopia often develops as people grow. It usually levels out once they've stopped growing. The development of myopia in adulthood sometimes coincides with intense close work. It may also be a sign of diabetic problems, or the start of cataracts. If you have mild myopia you may notice difficulty reading the scores on TV, or trouble with road signs. With increasing myopia, things in the distance get blurrier, and they don't have to be as far away before the blurriness is noticeable. Someone with a high degree of myopia might not be able to see anything clearly unless it is right up close to their eyes. Most people with myopia still have good vision for things up close - hence they are 'short-sighted'.
Hyperopia - Long-sightedness
The opposite of myopia is hyperopia, and it is usually caused by an eyeball that is too short, or whose lenses are not powerful enough. People who have hyperopia see more poorly up close than they do in the long distance. Often long-sightedness emerges quite early in life, and will usually stay quite stable over time. Children with hyperopia will often be prescribed lenses just for reading and school-work.
People in their 50s and 60s sometimes develop long-sightedness. Long-sightedness puts extra demands on the focussing system, especially when looking at things up close. The effect of long-sightedness on the vision depends on how longsighted a person is, and also how old they are. When mild, it may just cause tired/ strained eyes with close work, but not affect longer-distance vision. Higher amounts of long-sightedness, especially in older people, would cause blurring at all distances.
Astigmatism is another focus error, and may be found together with short- or long-sightedness. In astigmatism, the focus of the eyes varies with orientation - for instance, stronger in the vertical plane, and weaker in the horizontal. Astigmatism adds blur to objects at any distance. It is usually caused by the cornea of the eye being irregularly shaped. It is more curved in one direction than the other, in the same way that a football compares to a soccer ball.
Not only do eyes need to be in focus, they need to work well together. There are twelve muscles that control eye movements. If their function or co-ordination is lacking, eye strain, reading problems or double vision may result. Eye movements also relate to the amount of effort the eyes use to focus close-up. So we sometimes use lenses to help with eye co-ordination.
Presbyopia - 'eyes after 40'
The ability of the eyes to change their point of focus diminishes over time. This is because the lens inside the eye, which flexes to adjust the eye's focus, gradually gets stiffer. Everyone's experience varies, but usually the first thing noticed is difficulty with small print, or in poor light. Sight then worsens over the next few years until most things up close are blurred. All sorts of solutions have been tried down through time to try and stop this natural aging process, but without success. The only solution is to use Lenses to assist with reading by compensating for the eye's inability to focus up close.
How can Sharpe and Fowler help?
Any of the above conditions - myopia, long-sightedness, astigmatism, presbyopia — and others — can give rise to symptoms of blurred or uncomfortable vision. Part of our eye exam is to determine the errors of focus in each eyes, and to assess how well the two eyes work together. We can let you know the health of your eyes, and advise the most appropriate form of visual correction if needed.