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Prism (optics) An optical prism is a transparent optical element with flat, polished surfaces that are designed to refract light. At least one surface must be angled — elements with two parallel surfaces are not prisms. The most familiar type of optical prism is the triangular prism, which has a triangular base and rectangular sides.
Halo (optical phenomenon) A halo (from Ancient Greek ἅλως (hálōs) 'threshing floor, disk') [1] is an optical phenomenon produced by light (typically from the Sun or Moon) interacting with ice crystals suspended in the atmosphere. Halos can have many forms, ranging from colored or white rings to arcs and spots in the sky.
The prism cover test ( PCT) is an objective measurement and the gold standard in measuring strabismus, i.e. ocular misalignment, or a deviation of the eye. [1] It is used by ophthalmologists and orthoptists in order to measure the vertical and horizontal deviation and includes both manifest and latent components. [1]
Nicol prism. A Nicol prism is a type of polarizer. It is an optical device made from calcite crystal used to convert ordinary light into plane polarized light. It is made in such a way that it eliminates one of the rays by total internal reflection, i.e. the ordinary ray is eliminated and only the extraordinary ray is transmitted through the ...
Dispersion (optics) In a dispersive prism, material dispersion (a wavelength -dependent refractive index) causes different colors to refract at different angles, splitting white light into a spectrum. In optics and in wave propagation in general, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency; [1 ...
The glasses are placed in the trial frames with the striations vertical, giving rise to two horizontal line images when viewing a spotlight. If the patient has a vertical deviation, the lines will be seen one above the other. If there is little or no vertical separation, vertical prism can be used to separate the lines.
A dichroic prism is a prism that splits light into two beams of differing wavelengths (colour). A trichroic prism assembly combines two dichroic prisms to split an image into 3 colours, typically as red, green and blue of the RGB colour model. They are usually constructed of one or more glass prisms with dichroic optical coatings that ...
Prism dioptres. Prism correction is commonly specified in prism dioptres, a unit of angular measurement that is loosely related to the dioptre. Prism dioptres are represented by the Greek symbol delta (Δ) in superscript. A prism of power 1 Δ would produce 1 unit of displacement for an object held 100 units from the prism. [2]
Eye glasses with an included prism power is the optical method to reduce a fixation disparity. Different procedures have been proposed to determine the required amount of prism for the individual. Based on prism-FD curves (Fig. 3b), one can find the aligning prism sP 0 that nullifies the naturally prevailing fixation disparity sFD 0. This test ...
A Wollaston prism is an optical device, invented by William Hyde Wollaston, that manipulates polarized light. It separates light into two separate linearly polarized outgoing beams with orthogonal polarization. [1] The two beams will be polarized according to the optical axis of the two right angle prisms. The Wollaston prism consists of two ...
