Laser surgery and refractive errors

Excimer laser is now safe and reliable alternative to the spectacle and contact lens correction of refractive errors of the eye. The essence of excimer laser surgery is a change of curvature of the cornea of the human eye by ablation of particular amount of tissue at a particular place on the front surface of cornea. In myopia the central cornea is flattened, aggravated in farsightedness and adjusted only in a particular axis in astigmatism cases. This is how correction of refractive error and change of dioptric power of the optical system of the whole eye (change of refraction) as a final result is achieved.

HOW DOES THE EYE WORK

In a healthy, perfectly focusing eye, light passes into the eye through the iris and pupil into a point of sharp focus that ideally should centre on your retina. Photoreceptors on the retina translate the light signal into electric impulses. The optic nerve sends messages to your brain, which translates the message into a picture – we understand this as ‘vision’. In other words the eye works in exactly the same way as a digital camera, but the picture is displayed on the camera’s screen.

What is a refractive error

The eye’s ability to refract or focus light sharply on the retina is based on two main anatomic features: the overall length of the eye and the curvature of the eye’s surface or cornea.
In most eyes, the correct balance of these two features does not exist. This is what we call a refractive error.

Myopia – shortsightedness – the image focuses in front of the retina
Hyperopia – long-sightedness the image focuses behind the retina
and with Astigmatism two focal points fall in two different positions on the retina
 

Myopia or shortsightedness (negative refractive error)

Myopia is a condition in which an image of a distant object becomes focused in front the retina, either because the eyeball axis is too long, or because the refractive power of the eye is too strong. This condition makes nearby object appear in focus and distant objects out of focus.
Excimer laser eye surgery is recommended for refractive errors in the range of  - 0.5 – 12.0 D.

Hyperopia or longsightedness (positive (+) refractive error

Hyperopia is the refractive error in which an image of a distant object becomes focused behind the retina, either because the eyeball axis is too short, or because the refractive power of the eye is too weak. This condition makes close or distant objects appear out of focus.
Excimer laser eye surgery is recommended for refractive errors in the range of  +1.0 to + 6.0 D.

Astigmatism (cylindrical refractive error)

Astigmatism is a condition in which an abnormal curvature of the cornea can cause two or more focal points to fall in different locations on the retina - making close or distant objects appear blurred or double. Unless the astigmatism is irregular, the range for the excimer laser eye surgery is not limited but most often +/- 7.0 Dcyl.