1. Assessing the Need for Iris Registration System with Active Tracking Capability Julio Narvaez, MD; Peter Bekendam, MD; Kristin Schmid, BS; Gregory Bacon, BS

2. Financial Interest Disclosure None of the coauthors have financial relationships with any of the products mentioned in this presentation.

3. Purpose To determine the utility of an Iris Registration system equipped with an active tracking capability for yielding more precisely aligned ablation in refractive surgery.

4. Introduction The VISX Iris Registration system uses individual landmarks on the iris to align the laser with images taken during pre-operative measurements, thereby largely eliminating the problems of cyclorotation and centroid shift that occur between preoperative measurements and the actual procedure. The VISX Iris Registration system, however, is not currently equipped with active tracking capabilities, so it cannot correct for any cyclorotation or axial shift that may occur after it has been engaged at the start of the refractive procedure. If any further axial shift or cyclorotation occurs between the time of Iris Registration engagement and the actual ablation, a suboptimal refractive result could occur.

5. Methods The charts of 34 consecutive patients undergoing custom-view refractive surgery utilizing the WaveScan Wavefront system (VISX Inc, Santa Clara, Calif) for pre- operative measurements. Data were reviewed on a total of 59 eyes. The degree of cyclorotation and axial decentration (X and Y axes) were noted at two points in time: at initiation of iris registration at the beginning of the procedure, and then again at a second iris registration performed later in the surgery immediately prior to ablation. These two measurements were then compared to determine the degree of intra-operative cyclorotation and axial decentration.

6. Results One sample t test was used to assess the difference between the two measurements (initial and intra-operative). Data were log transformed to meet parametric assumptions of the one sample t-test. Comparison of the amount of intraoperative cycloration and axial decentration showed a statistically significant degree of cycloratation as well as shift in the y axis, but not in the x axis (see table on the following slide).

7. Results MeanSDMedianRangeP value Diff C 1 1.772.0551.200-120.000 Diff X 2 0.13110.251910.070-1.840.186 Diff Y 3 0.12930.139630.080-0.750.000 1.The difference of cyclorotation in units of degrees 2.The difference of central adjustment in the X axis in millimeters 3.The difference of central adjustment in the Y axis in millimeters

8. Discussion This study demonstrates that a statistically significant amount of corneal decentration occurs after initiation of Iris Registration and before ablation. This suggests that an iris registration system with active tracking capabilities might be useful in maintaining alignment and performing more precise ablations