| parallax test | Measurement of the deviation in strabismus by the alternate cover test combined with neutralization of the deviation using prisms. (05 Mar 2000) |
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| binocular parallax | The difference in the angles formed by the lines of sight to two objects situated at different distances from the eyes; a factor in the visual perception of depth. Synonym: stereoscopic parallax. (05 Mar 2000) |
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| parallax | 1. The apparent displacement, or difference of position, of an object, as seen from two different stations, or points of view. 2. <astronomy> The apparent difference in position of a body (as the sun, or a star) as seen from some point on the earth's surface, and as seen from some other conventional point, as the earth's center or the sun. Annual parallax, the greatest value of the heliocentric parallax, or the greatest annual apparent change of place of a body as seen from the earth and sun; as, the annual parallax of a fixed star. Binocular parallax, the apparent difference in position of an object as seen separately by one eye, and then by the other, the head remaining unmoved. Diurnal, or Geocentric, parallax, the parallax of a body with reference to the earth's center. This is the kind of parallax that is generally understood when the term is used without qualification. Heliocentric parallax, the parallax of a body with reference to the sun, or the angle subtended at the body by lines drawn from it to the earth and sun; as, the heliocentric parallax of a planet. Horizontal parallax, the geocentric parallx of a heavenly body when in the horizon, or the angle subtended at the body by the earth's radius. Optical parallax, the apparent displacement in position undergone by an object when viewed by either eye singly. Parallax of the cross wires (of an optical instrument), their apparent displacement when the eye changes its position, caused by their not being exactly in the focus of the object glass. Stellar parallax, the annual parallax of a fixed star. Origin: Gr. Alternation, the mutual inclination of two lines forming an angle, fr. To change a little, go aside, deviate; beside, beyond + to change: cf. F. Parallaxe. Cf. Parallel. Source: Websters Dictionary (01 Mar 1998) |
| parallax method | Localization of a foreign body by observing the direction of its motion on a fluoroscopic screen while moving the X-ray tube or the screen. (05 Mar 2000) |
| vertical parallax | The relative vertical displacement of the image when each eye is closed in turn; seen in vertical diplopia, or heterophoria. (05 Mar 2000) |
| heteronymous parallax | The apparent movement of an object toward the closed eye; noted in exophoria. (05 Mar 2000) |
| homonymous parallax | The apparent movement of an object toward the open eye when one is closed; noted in oesophoria. (05 Mar 2000) |
| stereoscopic parallax | The difference in the angles formed by the lines of sight to two objects situated at different distances from the eyes; a factor in the visual perception of depth. Synonym: stereoscopic parallax. (05 Mar 2000) |
| Abbe test plate | <equipment> A long, wedge-shaped coverslip about 0.20 mm thick at one end and 0.10 to 0.12 mm at the other end coated chemically with a silver film on which are ruled horizontal lines. at each variation in thickness of 0.01 mm there are vertical lines. By means of oblique illumination and by focusing on different portions of the plate, it is possible to determine the optimum coverslip thickness for any objective and also, for microscopes with drawtubes, the tube length for best objective performance. The approximate freedom from spherical and chromatic aberrations can also be estimated. Small isolated bits of silver near the edges of the lines form good objects for the star test (05 Aug 1998) |
| acetone test | A test for ketonuria; the suspected urine is shaken up with a few drops of sodium nitroprusside, and strong ammonia water is then gently poured over the mixture; if acetone is present, a magenta ring forms at the line of contact; tablets containing sodium nitroprusside and alkali are now more commonly used. (05 Mar 2000) |
| achievement test | A standardised test used to measure acquired learning, e.g., competence in a specific subject area such as reading or arithmetic, in contrast to an intelligence test which is a useful index of potential ability or learning. (05 Mar 2000) |
| acidified serum test | Lysis of the patient's red cells in acidified fresh serum, specific for paroxysmal nocturnal haemoglobinuria. Synonym: Ham's test. (05 Mar 2000) |
| acid loading test | <nephrology> This is a test used in the diagnosis of renal tubular acidosis. The patient takes ammonium chloride capsules for 3 days to acidify the blood (lower blood pH). A sample of the urine and the blood is then collected and the results are interpreted. (27 Sep 1997) |
| acid perfusion test | <gastroenterology, investigation> A test used to diagnosis gastrooesophageal reflux disease. This investigation requires that the patient swallow 3 tiny tubes into the stomach. A mixture of hydrochloric acid (like stomach acid) and saline are alternatively injected into the tubes. The patient then reports any symptoms they may have. Some patients may vomit. (13 Nov 1997) |
| acid phosphatase test for semen | A screening test for semen by determining acid phosphatase content; because seminal fluid contains high concentrations of acid phosphatase, while other body fluids and extraneous foreign materials have very low concentrations, high values of acid phosphatase on vaginal aspirate or lavage, or on wash fluid from stains, render positive identification of semen, even if the male is aspermic. (05 Mar 2000) |
| acid reflux test | A test to detect gastroesophageal reflux by monitoring oesophageal pH by an electrode in the distal oesophagus either basally or after acid is instilled into the stomach. (05 Mar 2000) |