Determining scotopic pupil size

Abstract

Reply: We would like to thank Khanani and Brown for their interst in our paper comparing different devices to determine scotopic pupil sizes. First, we do not think it matters that the measurements were conducted bilaterally since we compared only measurements between different methods but not intraindividual or interindividual variations in PD. Moreover, the concern that Colvard measurements could be affected by bilaterality is pure speculation and not proven by earlier studies. The term “gold standard” or “gold standard accuracy” was not used in our article. Khanani and Brown named the Procyon pupillometer the gold standard; we did not claim it was the gold standard, only that the PD values measured with the Procyon pupillometer were considered reference values in the comparison study we performed. The implication that we regard as the gold standard a device providing the largest PD values and that we rely on its accuracy for design or cost is pure fiction. We also did not claim that “clinicians should base their decisions on machine-specific scotopic PD values.” We stated that these values should be taken into consideration when planning a refractive surgical procedure. We agree with Khanani and Brown that scotopic pupil size has been determined for decades and newer approaches may have found different values. But the measurement of pupil size with digital infrared pupillometers seems to be the most precise and practical way to evaluate this factor for refractive surgery, particularly because they measure continual unrest and anisocoria. Thomas Kohnen MD Evdoxia Terzi MD Thomas Kasper MD Eva-Maria Kohnen MD Jens Bühren MD