Laser photocoagulation spot-size errors stemming from the refractive stateof the surgeon's eye

Purpose: Meaningful errors in photocoagulation spot size may result from se veral factors. In this article we discuss one major factor, namely, fluctua tions in the surgeon's accommodative state, coupled with an inaccurate sett ing of the slit-lamp oculars. Design: Experimental study. Methods: We analyzed and tested the optics of slit-lamp mounted lasers. Var ying the ocular setting is correlated with measurements of the actual spot size obtained with each system. Main Outcome Measure: The spot size obtained. Results: Three distinct, but related, phenomena that may lead to spot size errors are;defined: (1) focusing the laser spot as opposed to focusing the retinal image; (2) instrument misalignment; (3) inadvertent accommodation. Conclusion: The ocular setting must be meticulously calibrated to produce a true spot-sized burn. At the 50 mu m setting, each diopter of induced acco mmodation, or erroneous ocular setting, almost doubles the actual spot size obtained. With large (500 mu m) spot size settings, the defocused delivery system is move prone to spot-size errors in contrast with parfocal lasers. (C) 2000 by the American Academy of Ophthalmology.