Urologist's visual color blindness caused by laser safety goggles

Lasers are often used in intracorporeal endoscopic lithotripsy. However, lasers may expose the urologist to hazardous laser energy that may injure the macula and fovea. To avoid ocular injury, laser safety goggles are worn. Each goggle is tinted which imparts color distortion. However, it is axiomatic that normal vision of the urologist enhances ease and safety of surgery. This study tested color discrimination among urologists using different goggles, and assessed and quantified visual impairment. Consecutive subjects (urologists) underwent a Farnsworth Dichotomous Test for Color Blindness (D-15), a standardized screening test of color blindness where subjects match equal hue steps in the natural color circle. Subjects then underwent a Farnsworth-Munsell (FM) 100-hue test to measure areas of color confusion. Subjects were tested without goggles (control), and with goggles for coumarin green, Alexandrite, and HoTmiumiYAG. Subjects were also asked to rate which matching color sets were problematic to differentiate for each set of goggles. Statisical analysis was done with chi-square for the D-15, and t-test on Aspinall's square root transformation of the error score for the FM. All 15 subjects tested within normal limits on the D-15 and FM tests without goggles and with Holmium:YAG goggles. On the D-15, subjects had % errors (mean ±standard deviation) for coumarin green, CO₂, and Alexandrite goggles of 43110, 2±0, andO±0, respectively (p<0.01). On the more sensitive FM test, the error scores (mean ±standard deviation) for coumarin green, Alexandrite, Holmium:YAG, and control (no goggles) were 319 ±69, 91 ±32, 20 ±12, and 20 ±14, respectively (p<0.05). The difficult color matches were consistent for all subjects: (1) coumarin green both blue-green and lavender; (2) Alexandrite both bluegreen and lavender; and (3) HolmiumiYAG none. The data shows that coumarin green safety goggles impair color vision and discrimination more than the Alexandrite or Holmium:YAG goggles. Holmium:YAG goggles impair color vision and discrimination the least and provide the most natural color vision among goggles tested. These results suggest that surgical vision is least affected by safety goggles for Holmium:YAG.