Vision Correction

The human eye is a complex mechanism in many ways similar to a camera. Just as the camera records images on a film, the eye records them on a special layer called the retina. Just like the camera needs lenses to focus images on the film, the eye also has lenses to focus images on the retina. The eye has two lenses: the cornea and the "lens". The cornea is a fixed focus lens. It simply bends light rays by a fixed amount. The lens is like an auto focus system. It changes its shape to focus images perfectly on the retina, so that images appear sharp and crisp.

Sometimes when there is a mismatch between the curvature of the cornea, power of the lens and the length of the eye, the eye focuses images ahead of or behind the retina. This is known as refractive error. This results in unclear vision, eyestrain and headaches. To eliminate this mismatch, spectacles or contact lenses need to be worn.

In ordinary circumstances, the curvature of the cornea, the power of the lens and the length of the eye are finely coordinated to focus images perfectly on the retina and thereby produce clear, strain free vision. Sometimes this system fails and light rays focus the image ahead or behind the retina. This results in unclear vision, eyestrain and headaches. These conditions are known as refractive errors and can be of the following types:

Technically called myopia, nearsightedness means you have trouble seeing and resolving objects at a distance. When the eye is too long in relation to the curvature of the cornea, images focus in front of the retina instead of on it and objects at distances appear blurred. Patients with myopia are able to see near objects.

Technically called hyperopia, farsightedness means you have trouble with close up vision. It occurs when the eye is functionally too short. The rays of light are focused behind the retina producing a blurred image. Some people who are farsighted are able to use their focusing muscle (accommodation) to bring the image forward allowing them to see clearly. This ability worsens with age and reading glasses or bifocals may be needed. Farsighted people see distant objects more clearly than near objects.

The normal solution for refractive errors is to wear spectacles or contact lenses to see clearly. There is one other condition for which people normally need to wear glasses. This condition is normally associated with ageing, and is known as presbyopia.

Presbyopia is a normal ageing process. As we get older, the lens loses its ability to flex and focus at near. The onset of presbyopia typically is between 40 and 50. When this occurs people who already wear glasses may need bifocals and those who have never worn glasses may require reading glasses. Presbyopia is an important concept to understand, if you are over 40, and if you are considering laser correction. One advantage of mild nearsightedness (myopia) is the ability to remove your glasses after presbyopia sets in and still be able to read. If you have Laser Vision Correction for nearsightedness, you will lose this ability. That's because your vision typically becomes normal, and for the ageing eye usually will require reading glasses for small print. The excimer laser has no effect on your focusing muscles and therefore cannot treat presbyopia. However, there are ways around this problem, and it is best to talk to one of our expert eye doctors to discuss the best solution for you.

Many patients with myopia or hyperopia have some degree of astigmatism. This means that your eye is slightly oval and your cornea is shaped like a football rather than a sphere. People with astigmatism experience, distortion or tilting of images due to the unequal bending of rays of light entering your eyes. High degrees of astigmatism will cause blurred vision for distant and near objects.