Visual ambiguity or distortion occurs as a result of the “systematic departures of perceptual measurements of a stimulus from its physical measurements” (Craighead, Corsini, & Nemeroff, 2002, p. 1742). A case which involves the occurrence of visual ambiguity occurs during instances when a person experiences double vision. Double vision or diplopia refers to “the misalignment of the visual axes and the loss of binocular fusion” thereby leading to the misperception of one object as two objects (Mladenovic, 2003, p. 142).
Double vision may either be physiological or pathological. Physiological double vision also known as fixation disparity occurs ‘when two images of an object fall on disparate points on the retina’ (Agarwal, Apple, & Burrato, 2002, p. 433). As opposed to physiological double vision, pathological vision may either be uniocular or binocular in character. Uniocular double vision has three forms: (1) ‘physical uniocular double vision,’ (2) ‘projectional uniocular double vision,’ and (3) ‘central uniocular double vision’ (Agarwal et. al. , 2002, p. 433).
Physical uniocular double vision occurs as a result of “optical causes in the eye such as keratoconus, iridodialysis, double pupils, subluxation of the lens, spherophakia, incipient cataract and retinal detachment” (Agarwal et. al. , 2002, p. 433). Projectional uniocular double vision, on the other hand, occurs “when a single visual stimulus is localized in normal and abnormal directions” (Agarwal et. al. , 2002, p. 433). Finally, central uniocular double vision occurs as a result of ‘calcarine lesions, multiple sclerosis, and basal meningitis’ (Agarwal et.
al. , 2002, p. 433). As opposed to the different forms of uniocular double vision whose occurrence may largely be attributed to the existence of other optical conditions, binocular double vision largely occurs as a result of the disparate positions of the retina due to different conditions. Binocular double vision occurs when “one image is distinct (the true image)…whereas the other image is indistinct (false image)” (Agarwal et. al. , 2002, p. 433).
There are five forms of binocular double vision: (1) ‘uncrossed double vision,’ (2) ‘crossed double vision,’ (3) ‘paradoxical double vision,’ (4) ‘congruous double vision,’ and (5) ‘incongruous double vision’ (Agarwal et. al. , 2002, p. 434). Uncrossed double vision occurs when, in the convergent squint, “the image of the objects falls on the nasal side of the fovea…which receives light from the temporal fields… (thereby resulting to) the false image’s position on the outer side of the true image” (Agarwal et. al. , 2002, p. 434).
Crossed double vision, on the other hand, occurs when, in the divergent squint, “the image falls on the temporal side of the fovea… (which is) perceived from the nasal field” thereby resulting to the false image’s position on the outer lower side of the true image (Agarwal et. al. , 2002, p. 434). Paradoxical double vision occurs when, in the divergent squint, uncrossed double vision occurs whereas, in the convergent squint, crossed double vision occurs (Agarwal et. al. , 2002, p. 434). In the case of congruous double vision, ‘the distance of the double images leads to the deviation of the eyes’ (Agarwal et. al. , 2002, p. 434).
Finally, incongruous double vision occurs “when the distance between the double images…does not correspond to the angle of the squint” (Agarwal et. al. , 2002, p. 434). In either case of double vision (whether it is physiological or pathological in nature); one tends to perceive the true image along with the real image since the light falls on different parts of the retina of both eyes (Boothe, 2002, p. 269). For example, it may fall on the lower retina of the left eye and on the fovea of the right eye. As a result of this, the brain thereby receives contradictory information regarding the visual direction of the eye.
In order to resolve this contradiction, the brain compensates by assuming that two objects exist hence one perceives an additional false image of the true image of an object. References Agarwal, S. , Apple, D. , & Buratto, L. (2002). Textbook of Ophthalmology. Np: Jaypee Brothers Publishers. Boothe, R. (2002). Perception of the Visual Environment. London: Springer. Craighead, W. , Corsini, R. & Nemeroff, C. (2002). The Corsini Encyclopedia of Psychology and Behavioral Science. Np: John Wiley & Sons. Mladenovic, J. (2003). Primary Care Secrets. London: Elsevier Health Services.