Purpose: To treat irregular astigmatism by applying separate appropriate treatments in each of the two distinct hemidivisions of the cornea.
Setting: Cheltenham Eye Centre, Melbourne, Australia.
Methods: Two general surgical strategies are presented. The first applies the principles of optimization separately to each corneal hemidivision to achieve the maximum reduction in astigmatism when measured topographically and refractively. The second is for targeting symmetrical orthogonal topographic goals for each semimeridian to create the regular state in differing ways. These are performed in one of the following ways: without changing refractive astigmatism; by reducing the associated ocular residual astigmatism; by shifting the less favorably placed topography semimeridian to the other more favorably located one; by shifting both topographic semimeridians to more favorably located sites. This is an alternative when a potential improvement in the best corrected visual acuity is sought and the maximum reduction of astigmatism is not the priority.
Results: The calculated treatments necessary to achieve various improved astigmatic states, together with each of their respective separate refractive astigmatism targets, are presented. A single refractive astigmatism value for the entire cornea is also calculated by vector summation.
Conclusion: Consideration of each of the two distinct hemidivisions of the eye enables improved treatment of irregular astigmatism, potentially resulting in improved visual outcomes.