Differentiation from physiological afterimages<unk>  is a pathological symptom and should be distinguished from physiological afterimages, a common and benign phenomenon. Physiological afterimages appear when viewing a bright stimulus and shifting visual focus. For example, after staring at a computer screen and looking away, a vague afterimage of the screen remains in the visual field. A stimulus consistently produces the same afterimage, which is dependent on the stimulus intensity and contrast, the time of fixation, and the retinal adaptation state. Physiological afterimages are usually the complementary color of the original stimulus (negative afterimage), while palinoptic afterimages are usually the same color as the original stimulus (positive afterimage). There is some ambiguity between illusory<unk>  and physiological afterimages since there are not concrete symptomatic criteria which determines if an afterimage is pathological. Illusory versus hallucinatory Illusory<unk>  is due to an abnormality in the original perception of a stimulus and is similar to a visual illusion: the distorted perception of a real external stimulus. Hallucinatory<unk>  is due to an abnormality after a stimulus has been encoded in visual memory and is similar to a complex visual hallucination: the creation of a formed visual image where none exists. External conditions such as stimulus intensity, background contrast, fixation, and movement typically affect the generation and severity of illusory<unk>  but not hallucinatory<unk> . Illusory<unk>  consists of afterimages that are short-lived or unformed, occur in the same location in the visual field as the original stimulus, and are continuous or predictable. Hallucinatory<unk>  describes formed afterimages and scenes that are lifelike, high-resolution, long-lasting, occur anywhere in the visual field, and are unpredictable. Illusory<unk>  are caused by diffuse neuronal pathology such as global alterations in neurotransmitter receptors, while hallucinatory<unk>  is typically caused by focal cortical pathology. The clinical characteristics that separate illusory from hallucinatory<unk>  also help differentiate and assess risk in visual illusions and hallucinations. Complex (formed) visual hallucinations are more worrisome than simple visual hallucinations or visual illusions.
Palinopsia
Photopsia
Micropsia
Dysmorphopsia
Akinetopsia
Pelopsia
Agraphesthesia
Oscillopsia