Distortion and size calibration of the scanning laser ophthalmoscope (SLO) laser-beam raster.

PURPOSE: The Rodenstock scanning laser ophthalmoscope (SLO) is useful for mapping retinal function and for developing and evaluating visual rehabilitation methods. It is essential to know the visual angle subtended by stimuli in the SLO laser-beam raster and to accurately measure angular distances between objects in the final SLO image. To accomplish this, the angular extent of the SLO laser-beam raster must be calibrated. METHODS: We developed a simple method and apparatus for calibrating the raster and used it for repeated calibrations during a 3-month period. RESULTS: The laser-beam raster is quite stable in shape and size, but it is trapezoidally distorted in the vertical direction. Consequently, SLO images are distorted. CONCLUSIONS: Trapezoidal distortion of the SLO laser-beam raster can cause stimulus size to change as much as 10% from the top to the bottom of the raster. Measurements of fixed horizontal retinal landmark distances in SLO images can also vary as much as 10%. We developed a straightforward mathematical method for correcting distortion in SLO image measurements.     

Glossopharyngeal neuralgia; a cause of cardiac arrest

Glossopharyngeal tic douloureux or neuralgia is a comparatively rare but well-recognized syndrome. In respect to the stabbing paroxysmal nature of the pain and its relation to specific trigger zones, it is exactly comparable to the commoner trigeminal tic douloureux. In neurosurgical clinics the two types of neuralgia occur in a ratio of about one to forty.The significance of cardiac arrest and syncope associated with glossopharyngeal neuralgia was first emphasized by Riley and associates,¹ in a brief report of two cases in 1942. This report called attention to the afferent pathway of the carotid sinus reflex through the glossopharyngeal nerve and suggested the correlation of the simultaneous neuralgia and excessive stimuli to the sinus reflex. Neither of the two cases was reported to have been subjected to operation. Since then, no other reports of similar cases have come to light in medical literature. However, one of us (Ray) had the opportunity of examining such a case with Dr. Jefferson Browder in 1943 and this patient was relieved of all symptoms by intracranial section of the glossopharyngeal nerve.Because of the importance of further establishing the authenticity of the syndrome and calling wider attention to the importance of its recognition, there is justification for reporting another comparable case.