Sir: Hallucinogen persisting perception disorder is the reexperiencing of the perceptual symptoms experienced while intoxicated with the hallucinogen. Examples of these perceptual distortions include geometric hallucinations, false perceptions of movement in the peripheral visual fields, flashes of color, positive afterimages, macropsia, and micropsia. Various pharmacologic treatments of "flashbacks," including neuroleptics and benzodiazepines, and electroconvulsive therapy have met with limited success. 1 Case report. Mr. A, a 22-year-old male college student, presented to a college counseling center with symptoms of mild depression. Six months prior to his evaluation, he had stopped using lysergic acid diethylamide (LSD), after an 8-month history of LSD abuse during which he had used between 1000 to 1800 µg at least twice a week. Despite his abstinence, he noticed the persistence of LSD-like phenomena. These phenomena included visual illusions, trailing images, depersonalization, images in his peripheral field, and visions of colorful geometric forms when he closed his eyes. They occurred almost daily, were not distressing to the patient, and had preceded the onset of his depressive symptoms. He had no history of seizures or migraines.Antidepressant treatment was begun with sertraline 25 mg and was titrated upward slowly owing to concern about these flashbacks. Mild exacerbations of these LSD-like phenomena were noted for 2 to 4 days after each dosage increase, primarily as flashes of color, positive afterimages, and fleeting hallucinations in his peripheral vision. Within 1 month after the target dose of 100 mg was reached, these perceptual disturbances decreased until they had almost completely remitted. The depressive symptoms also improved. These gains were maintained for 4 months, at which point Mr. A graduated and terminated treatment.

There is a need for lasers that are compatible with fiberoptic endoscopes and that provide greater cutting precision than currently can be produced by the widely used Nd:YAG (1.06 micron) laser. Recently available lasers that operate in the 2-micron region fill this need. This laser light energy can be transmitted by low OH- silica fibers and has much less tissue penetration than radiation at 1.06 micron. We have been evaluating a prototype solid state laser system that produces pulses of 2.15 microns light that is delivered by a silica based fiberoptic delivery system with negligible transmission losses. This system is based on a thulium-holmium-chromium doped YAG (Tm-Ho-Cr: YAG) rod that lases at 2.15 micron. The laser does not require cryogenic cooling, toxic gases, or custom utilities and should be practical in a clinical environment. In vivo animal testing of this laser confirms that it provides greater ablating precision than does the Nd:YAG laser at 1.06 micron.

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