Advanced Optical Analysis of Divergence Between the Foci of the Nd:YAG and Aiming-Beam Lasers.

Purpose To evaluate the divergence between the neodymium-doped yttrium aluminum garnet (Nd:YAG) and the aiming diode laser beams foci. Design Optical analysis and measurements were performed using a Volk Goldmann 3-mirror lens with a Nidek YC-1800 Nd:YAG laser apparatus. Subjects None. Methods We used The Zemax OpticStudio (ZOS) program for the model of Nd:YAG treatment in a human eye. Additionally, theoretical calculations were performed. Main Outcome Measures The divergence between the Nd:YAG laser focus and the intersection of the two aiming beams inside the eye. Results Focal points of the two laser beams converge 8 mm behind the cornea. Posterior to this point, the intersection of the diode laser aiming beams lies in front of the focal point of the Nd:YAG treatment laser, with distance between the two foci progressively increasing up to 305 microns at 24 mm behind the cornea. Conclusions We report the degree of divergence between the two lasers’ focal points due to the difference in refraction between the corresponding wavelengths. These results have high practical relevance, as they provide a starting point for increasing the accuracy of Nd:YAG laser treatment, particularly when applied to the posterior segment, thereby minimizing the risk of complications. Current Nd:YAG laser devices have the built-in ability to modify the focal point of the aiming beam along the z-axis, thus providing possibility for an immediate application of our findings in clinical practice.