Evaluation of hyperopic photoablation profiles.

zones showed unstable results with an unacceptably high complication rate.1-3 This led to design of a 9.0 mm hyperopia ablation profile.4 Today, most laser manufacturers offer relatively large treatment zones for hyperopia. A 5.5 to 6.0 mm optical zone and 9.0 mm ablation zone diameter seems to be the current standard. Figure 1 shows some examples of nominal optical zone (OZ) and ablation zone (AZ) sizes. Despite this there still seems to be substantial differences in the clinical results of different lasers. These differences are caused possibly by a different ablation profile which defines the postoperative curvature on the corneal surface. Our definition of optical zone and ablation zone can also be seen in Figure 1. The optical zone extends from the center to the deepest point of the ablation. The ablation zone includes both the optical zone and the transition zone (TZ); AZ = OZ + TZ. For a certain ablation zone—often limited by the specific optical design of the laser—one can increase the optical zone only for the price of a steeper (smaller) transition zone. This may conflict with the major target for the transition zone: to avoid creation of abrupt changes in corneal curvature that stimulate strong epithelial regrowth.