| index myopia | Myopia arising from increased refractivity of the lens, as in nuclear sclerosis. (05 Mar 2000) |
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| index of refraction | <physics> For a given wavelength, this is the ratio of the velocity of light in vacuum (c) to the velocity of light in a refractive material (for example, glass, plasma, etc.). (09 Oct 1997) |
| invasion index | An index devised by Abercrombie & Heaysman as a means to estimate the invasiveness of cells in vitro. The index is derived from measurements on confronted explants of the cells and embryonic chick heart fibroblasts growing in tissue culture: it is the ratio of the estimated movement, had the cells not been hindered and the actual movement in the zone in which collision occurs. (18 Nov 1997) |
| iron index | An obsolete index of iron obtained by dividing the figure for the average content of iron in normal blood (42.74 mg) by the red cell count in millions; it normally varies between 8 and 9; in pernicious anaemia, the index is usually greater than 10, but it tends to be normal in chronic secondary anaemia. (05 Mar 2000) |
| obesity index | Body weight divided by body volume. (05 Mar 2000) |
| opsonic index | A value that indicates the relative content of opsonin in the blood of a person with an infectious disease, as evaluated in vitro in comparison with presumably normal blood; the opsonic index is calculated from the following equation: phagocytic index of normal serum ÷ phagocytic index of test serum = 1 ÷ x, where x represents the opsonic index. (05 Mar 2000) |
| optical index | <microscopy> A constant applied to objectives for purposes of comparison. It takes into account the focal length or magnifying power of the lens and also the numerical aperture. It was offered by Nelson and by Coles, but little use has been made of the optical index figure, probably because the equations of the two men differed and the resulting figures have been at variance. (05 Aug 1998) |
| oral hygiene index | A combination of the debris index and the dental calculus index to determine the status of oral hygiene. (12 Dec 1998) |
| orbital index | Relation of the height of the orbit to its width: (orbital height × 100)/orbital width. (05 Mar 2000) |
| orbitonasal index | The ratio of the width between the lateral angles of the eyes, measured with a tape measure passing over the root of the nose times 100, to the width between the lateral angles of the eyes measured with a caliper. (05 Mar 2000) |
| overlap index | <cell biology> A measure of the extent to which a population of cells in culture forms multilayers. The predicted amount of overlapping is calculated knowing the cell density, the projected area of the nucleus (usually) and assuming a Poisson distribution. The actual overlap is measured on fixed and stained preparations and the ratio of actual/predicted is derived. A value of 1 implies a random distribution with no constraint on overlapping, normal fibroblasts may have values as low as 0.05. Although a useful measure it does not unambiguously indicate the reason for the effect, which may be contact inhibition of locomotion or differential adhesion of cells between substratum and other cells. (18 Nov 1997) |
| therapeutic index | The ratio of LD50 to ED50, used in quantitative comparison of drugs. (05 Mar 2000) |
| thoracic index | Anteroposterior diameter of the thorax times 100 divided by the transverse diameter of the thorax. Synonym: chest index. (05 Mar 2000) |
| tibiofemoral index | The ratio obtained by multiplying the length of the tibia by 100 and dividing by the length of the femur. (05 Mar 2000) |
| effective temperature index | A composite index of environmental comfort which is compared after exposure to different combinations of air temperature, humidity, and movement. (05 Mar 2000) |