This phenomenon results in fluid accumulation, and the higher risk of central islands, decentered ablations, or irregular corneal astigmatism. Because of this phenomenon, broad beam lasers have been programmed to place additional pulses centrally unrelated to the reshaping task in order to eliminate the possibility of these central islands. Because each patient is different and not entirely predictable in advance, this is a gross fix for a subtle problem, and some irregularities in the bed are inevitable. This customized small spot programming eliminated the unpredictable fluid accumulation seen in brad beam lasers. The absence of fluid makes for a much more uniform and predictable ablation.
Corneal topography can demonstrate decentrations and other irregularities.
A broad beam laser of 6 mm is incapable of accommodating focused ablations of the cornea to compensate for minor corneal abnormalities that may only be in a 2 mm area. A smaller beam, such as the LSX beam of less than 1mm diameter, can be more easily programmed to take care of these small irregularities. All cataracts change over time, so this aberration would change over time. Treating a defect in the visual pathway by ablating a permanent change into the cornea will correct the aberration only temporarily -and as the cataract progresses over time, the programmed previous correction will be inappropriate. In fact, if irregular astigmatism were not primarily caused by the anterior surface of the cornea, rigid contact lenses would not have worked on this problem so well for the past half century.