These are the most common disorders found at an eye examination and all of them are corrected with spectacles or contact lenses.
Long Sight (Hypermetropia) This is the most common of the conditions that can be corrected with spectacles and is the result of the eyeball being too short so that light that should form a clear image on the retina at the back of the eye is focussed at a point behind the eye. The effort of trying to see clearly causes eye pain, headaches and blurred vision particularly with closer objects.
Short Sight (Myopia) - results from the eyeball being too long causing light to come to a focus in front of the retina which makes the image on the back of the eye blurred. Short sighted people have difficulty seeing objects that are farther away but can see close work very well.
Astigmatism - best considered as a mixture of long and short sight where some of the light focusses before the retina and some behind the eye. When looking at the spokes of a wheel some of them, say the horizontal ones, will appear clear whilst others, the vertical spokes, are blurred.
Presbyopia - ageing vision, a condition which will come to everyone in their mid-forties. This is caused by hardening of a little lens inside the eye. When the lens squeezed by a muscle in the eye it changes the focus so that we are able to see clearly when looking at close objects e.g. reading. As the lens becomes progressively harder with age it is less able to flex and bring the very close objects into clear focus. Over time (about 15 -20 years) more and more of the closer things are less clear and so in later life spectacles are needed most of the time.