Laser Surgery: Treatment of presbyopia with the excimer laser

Presbyopia, or age-related long-sightedness, involves a deterioration in the ability of the lens to focus well on objects that are close to the eye. It occurs between the ages of 45 and 50.

Traditionally, it has been corrected with glasses, either just for near vision or with bifocals when the condition is combined with short sightedness.

Until recently, two options existed for patients with presbyopia combined with short-sightedness who wanted to undergo laser surgery. The first, monovision, consists of correcting one eye for far vision and the other for near vision, so the patient adapts to using the appropriate eye for each distance. The other solution was to use the laser to correct the vision for distance and then wear glasses for close vision.

Thanks to advances in laser procedures to modify corneal asphericity, a technique to simultaneously correct a patient’s presbyopia and their problems in seeing at a distance now exists.

In photography, we know that when a camera focuses on a distant object, objects that are closer go out of focus and vice versa. However, if the size of the aperture is reduced, it becomes possible to focus the two objects, one close to the camera and the other at a distance, simultaneously on the same plane or photograph. This effect of allowing the cornea to bring objects that are close and those at a distance simultaneously into focus on the retina can be achieved by modifying corneal asphericity, in other words, by increasing the eye’s depth of field.

In a cornea with increased asphericity, the centre of the cornea has more dioptres than the edges. With this profile, when the pupil naturally contracts in order to see things that are near, the central part of the cornea which has more dioptres is being used. This enables the eye to focus and see things close up such as when reading or sewing.

For distance vision, the pupil dilates and gets bigger and so uses the part of the cornea that has been corrected for seeing things that are far away.

This way of selecting distance or near vision, which occurs naturally in the human eye based on the mechanism of contraction or dilation of the pupil, makes this treatment very efficient and patients quickly adapt to the change.

Due to the precision that is necessary for this procedure, it is always carried out using the all-laser LASIK procedure:

• The femtolaser is used to create a corneal flap.
• The Wavelight Allegretto 400 Hz Eye-Q excimer laser is used to increase the asphericity of the cornea and as a result augment the patient’s depth of field.