Optical illusion is a deception that misleads one's vision or sight. Visualization of something which is imaginary or unreal can be called an optical illusion. They are perceived image which do not exist and is different from reality. Optical illusion is an outcome of the process that takes place in the brain which causes a perception that does not match with the accurate and carnal dimensions of the stimulus source. Optical illusions are classified as literal optical illusions, physiological illusions, cognitive illusions and, pathological visual illusions.