Dim Flicker: An Endogenous Visual Percept and Its Disease Associations

Background/Objectives: Visual sensations from ocular structures are entoptic. They may include retinal vascular shadows, perifoveal leukocyte migration, and phosphenes during eye movement causing retinal deformation. Abnormal neural activity in the visual cortex and retina have been linked to migraine aura. This study described monosymptomatic episodes of an endogenous transparent flicker overlaid on an otherwise intact visual field in medical retina patients. Methods: Retrospective evaluation of four patients' records with comparable descriptions of seeing a flickering overlay in part of their visual field and individual descriptions of their experience with reference to an animated flicker simula-tion. Results: Four patients reported seeing a dim rhythmic flicker over their normal bin-ocular vision. The effect was strongest in low ambient light and faded in bright light and when one or both eyes were covered. Duration was seconds to minutes. Some flicker crossed the vertical midline and appeared to be from one eye. All four patients noticed a simulation flickering at 7 Hz similar to their flicker, however the frequency ranged from 5 to 10 Hz and varied in position, prominence, and frequency. Flicker occurred in three pa-tients during aerobic exercise and in two patients during nighttime awakenings without room lighting. Flicker was unrelated to ocular or systemic conditions. The flickering had no association to the migraine patients' visual auras. Conclusions: Dim flicker is a rhyth-mic translucent overlay on an otherwise normal visual field. Unlike a migraine aura, it does not spread or cause a headache. Associated ocular conditions were retinal venous congestion, central serous chorioretinopathy, and migraine with aura.