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Troxler's fading: When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear. Vanishing puzzle: A vanishing puzzle is a mechanical optical illusion showing different numbers of a certain object when parts of the puzzle are moved around. [4]
The Worth Four Light Test, also known as the Worth's four dot test or W4LT, is a clinical test mainly used for assessing a patient's degree of binocular vision and binocular single vision. Binocular vision involves an image being projected by each eye simultaneously into an area in space and being fused into a single image.
The four pigments in a bird's cone cells (in this example, estrildid finches) extend the range of color vision into the ultraviolet. [1]Tetrachromacy (from Ancient Greek tetra, meaning "four" and chroma, meaning "color") is the condition of possessing four independent channels for conveying color information, or possessing four types of cone cell in the eye.
Impressions of several natural phenomena and the principles of some optical toys have been attributed to persistence of vision. In 1768, Patrick D'Arcy recognised the effect in "the luminous ring that we see by turning a torch quickly, the fire wheels in the fireworks, the flattened spindle shape we see in a vibrating cord, the continuous circle we see in a cogwheel that turns with speed". [8]
Purkinje images are the reflections from the anterior and posterior surfaces of the cornea and the anterior and posterior surfaces of the lens. Although these first four reflections are not entoptic — they are seen by others who are looking at someone’s eye — Becker described how light can reflect from the posterior surface of the lens ...
Blue–red contrast demonstrating depth perception effects 3 Layers of depths "Rivers, Valleys & Mountains". Chromostereopsis is a visual illusion whereby the impression of depth is conveyed in two-dimensional color images, usually of red–blue or red–green colors, but can also be perceived with red–grey or blue–grey images.
F = back vertex power (in 1/metres), (essentially, the prescription for the lens, quoted in diopters). If the difference between the eyes is up to 3 diopters, iseikonic lenses can compensate. At a difference of 3 diopters the lenses would however be very visibly different—one lens would need to be at least 3 mm thicker and have a base curve ...
Zeiss Protar (Rudolph, 1890). The first Anastigmat was designed by Paul Rudolph for the German firm Carl Zeiss AG in 1890 and marketed as the Protar; [1]: 65–66(§103) it consisted of four elements in two groups, as an asymmetric arrangement of two cemented achromatic lens doublets and was improved to a five-element, two-group design in 1891, substituting a cemented triplet for the rear group.