The term optical illusion is used in a narrow and a broad sense. In the narrow sense, it denotes an illusion attributable to the optics of the eye. In the broad sense, it is used as an equivalent of the term "visual illusion, denoting any aberrant visual percept that has a basis in an object or stimulus deriving from the extracorporeal environment. This broad class is sometimes divided into "physical, "physiological, and "cognitive optical illusions. The latter division is based on the conventional assumption that some illusions tend to occur as a natural consequence of the physical properties of an object or stimulus, whereas others depend on the inherent workings of the perceptual system or on the interaction between the perceptual input picture and the mind's (or brain's) unconscious inferences pertaining to the nature of the physical world. However, in all three cases a percept is created that differs from the physical measurements of the stimulus source at hand. Depending on the guiding principles employed, optical illusions can be further divided into subgroups such as the "ambiguous illusion, "distortion illusion, "geometric-optical illusion, "paradox illusion, and "fiction illusion. Some well-known examples of optical illusions are the "Müller-Lyer illusion, the "Oppel-Kundt illusion, the "Poggendorff illusion, and the "Zöllner illusion. The German physicist Johann Joseph Oppel (1815-1894) has been credited with initiating the scientific study of optical illusions in 1854, after his attention had been drawn to certain regularly recurring flaws in his students' drawings.
References
Gregory, R.L. (1991). Putting illusions in their place. Perception, 20, 1-4.
Oppel, J.J. (1854/1855). Ueber geometrischoptische Täuschungen. (Zweite Nachlese.) In: Jahres-Bericht des physikalischen Vereins zu Frankfurt am Main, 37-47.
Rutten, F.J.Th. (1929). Psychologie der waarnem-ing. Een studie over gezichtsbedrog. Thesis University of Utrecht.
Dictionary of Hallucinations. J.D. Blom. 2010.