| optical isomers | Isomers differing only in the spatial arrangement of groups around a central atom. Optical isomers rotate the plane of polarized light in different directions. For all biological molecules in which the possibility of optical isomerism exists, only one of the isomers is functional. (18 Nov 1997) |
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| optical keratoplasty | Transplantation of transparent corneal tissue to replace a leukoma or scar that impairs vision. (05 Mar 2000) |
| optical microscope | <instrument, microscopy> A very ambiguous term since all microscopes involve optics, better to specify light, acoustic, X-ray or electron microscope, etc. (05 Aug 1998) |
| optical noise | <microscopy> Image defects that become especially conspicuous when the image is enhanced. In video microscopy, includes hot spots, mottle, uneven illumination, etc. (05 Aug 1998) |
| optical pachymeter | A lens and/or mirror used to measure corneal thickness. (05 Mar 2000) |
| optical righting reflexes | Visual stimuli that enable an animal to maintain the correct position of the head in space, by bringing about movements of the muscles of the neck and limbs. (05 Mar 2000) |
| optical rotatory dispersion | The method of measuring the dispersion of an optically active molecule to determine the relative magnitude of right- or left-handed components and sometimes structural features of the molecule. (12 Dec 1998) |
| optical scrambler | <microscopy> An optical device for scrambling the image of a non-uniform light source so that it now fills the condenser aperture uniformly without appreciable loss of total luminous flux through the microscope. The scrambler can be a simple loop of a single optical fibre with its ends appropriately polished (05 Aug 1998) |
| optical sectioning | <microscopy> The use of high numerical aperture objective and condenser lenses on a microscope to achieve a shallow depth of field. With a very shallow depth of field, objects above and below focus contribute little to the in-focus image, so that a clean optical section is obtained. See: depth of field. (05 Aug 1998) |
| optical staining | <microscopy> Producing colour in the microscopical image so as to differentiate one part of the object from another. One way is by use of Rheinberg filters. Another is to use polarized light on an anisotropic specimen. Another important method is by dispersion staining. (05 Aug 1998) |
| optical storage devices | A computer disk read by a laser beam, containing data prerecorded by a vendor. The buyer cannot enter or modify data in any way but the advantages lie in the speed of accessibility, relative immunity to damage, and relatively low cost of purchase. (12 Dec 1998) |
| optical transfer function | <microscopy> The relationship between the image produced by an optical instrument and the amplitude and phase of a periodic specimen, measured at various spatial frequencies. The optical transfer function curve, which shows how well contrast is maintained for finer specimen details, is a complex function, of which the real term gives the ratio of amplitudes, and the imaginary term the phase relationships. When the brightness of the periodic specimen varies as a sine wave, the modulus or absolute value of the optical transfer function becomes the modulation transfer function, when the brightness varies as a square wave, the modulation transfer function is known as a contrast transfer function. Acronym: OTF (26 Mar 1998) |
| optical tubelength | <microscopy> The distance from the second principal focal plane of the objective to the front focal plane of the ocular. This distance is about 180 mm for high-power objectives, less for those of low power. (05 Aug 1998) |
| electron optical axis | <physics> The path of an electron through an electron optical system along which it suffers no deflection due to lens fields. This axis does not necessarily coincide with the mechanical axis of the system. (05 Aug 1998) |
| electron optical system | <apparatus> A combination of parts capable of producing and controlling a beam of electrons to produce an image of an object. (05 Aug 1998) |