How
the eye works
In order to understand what refractive surgery is and how it works it is important to know how the eye works and what refractive errors are.
Mechanism
of the eye
The eye works a lot like a simple camera. Light rays pass through the eye to focus on the retina at the back of the eye. This image is then transmitted to the brain.
The cornea is the first surface the light rays hit, the cornea is clear and does not stop the light rays but does bend the light significantly so that it can pass through the pupil towards the retina.
The lens inside the eye does the fine tuning of the focus of the image. The iris (coloured part of the eye) works like the aperture of a camera and regulates the amount of light entering the eye.
Refractive
errors
» Myopia (shortsightedness)
In a shortsighted eye, the light rays focus in front of the retina. This causes a blurred image at the retina. This occurs because the eye is too long or the cornea is too steep. Generally, shortsighted people can see images up close but have most difficulty with objects at a distance.
» Hyperopia (longsightedness)
In a longsighted eye, the rays of would come to focus behind the retina. This occurs if the cornea is too flat or the eye is too short. Generally, longsighted people can see objects better at a distance and have most trouble with near objects and reading.
» Astigmatism
Astigmatism
is when the curvature of the cornea is more like an egg rather than a
ball. This causes the light rays to be bent in different directions as
it passes through the cornea, the light can therefore not come together
and cause a blurred image at the retina.
Astigmatism can occur on its own or more commonly in conjunction with short and long sightedness. Generally people with astigmatism have a slight blur at all distances.
As we cannot change the length of the eye refractive surgery works by changing the curvature of the cornea to change the way light is bent as it passes through the eye to refocus the light at the retina.
