Yet, there is enough commonality between the main entoptic phenomena that their physical origin is now well understood. They are also unlike most optical illusions which are produced by viewing a common stimulus. Because of the variation between individuals, and the inability for two observers to share a nearly identical stimulus, these phenomena are unlike most visual sensations. This variance is not surprising because the specific aspects of the eye that produce these images are unique to each individual. Helmholtz commented on entoptic phenomena which could be seen easily by some observers, but could not be seen at all by others. Because entoptic images are caused by phenomena within the observer's own eye, they share one feature with optical illusions and hallucinations: the observer cannot share a direct and specific view of the phenomenon with others. Hence, they are different from optical illusions, which are caused by the visual system and characterized by a visual percept that (loosely said) appears to differ from reality. Spencer S.Entoptic images have a physical basis in the image cast upon the retina. For further information regarding the rights to this collection, please visit: Eccles Health Sciences Library, University of UtahĬopyright 2019. So positive visual phenomenon mostly migraine. And you got to differentiate it from photopisas which is just, "I see a flashing light" which is almost always a retinal sign. So if you just knew these three main categories, entoptic phenomenon, migraine aura or an occipital seizure, that's most of the positive phenomena that we see. Lasts seconds at a time they might have mental status changes or generalized. So small colored circles seconds at a time, bilateral, simultaneous, that is almost always occipital in origin and occipital seizures is what we're going to be worried about. In contrast, occipital seizure is usually not this jagged line It usually lasts seconds at a time and its geometric, small, little circles. So a bilateral, geometric, fortification, scintillating, colored or flashing scotoma that starts small and gets bigger lasts about 20 minutes and the headache follows that's going to be compatible with migraine. There might be colors in it and the colors might be flashing off and on and that's what we call a scintillation scotoma. The key differentiating features is the geometric nature of the phenomenon which we call a fortification scotoma because it looked like an old fort would look like in the old days and it typically starts small and gets bigger and moves across the visual field. If its bilateral we'd like to know the character of the phenomenon and migraine is a super common bilateral simultaneous and often hemianoptic positive visual phenomenon. So unilateral we've been thinking about entoptic phenomenon, flashing lights. So the retina cannot make a formed visual image, so it either makes flashing lights or nothing, that's pretty much what it can do. So patients with retinal detachments or posterior detachments or floaters might say I see a flashing light. Ent mean in and optic means eye and the most common causes of entoptic phenomena are vitreous traction, posterior vitreous detachment, retinal detachment. The most common unilateral visual positive phenomena that we have is called entoptic phenomena. In general, if its unilateral its in the eye and if its bilateral its in your brain. We like to know if its one eye or two eyes. And when patients complain about positive visual phenomena it's good to ask them to draw it. A flashing light, a jagged line, something like that. So positive visual phenomenon the patient will say I see something. So we are going to be covering positive visual phenomenon. Lee lectures medical students on positive visual phenomena.
Lee, MD, Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, TX Professor of Ophthalmology, Weill Cornell Medicine Peter Wojcik, Baylor College of Medicine Class of 2020ĭr.
Pathology, Signs and Symptoms, Migraines, SeizuresĪndrew G. Positive Visual Phenomena I: Entopic, Migraine Occipital Seizures Positive_visual_phenomenon_Part_I_Entoptic_Migraine_Occipital_Seizures
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