A METRO METER

n. _?m’e%t-uSr, For deriv., see AMETROPIA and -meter.* Fr., amétromètre. Ger., Ametromeler. It., a metro metro. Sp., ametrômetro. An instrument for the rapid detection of the degree of ametropia. Thomson's a. consists of a small gas-jet, A, and a second one, B, the latter sliding on a bar, D, the two jets being connected by a piece of rubber tubing, G, and supplied with gas through a thimble, H, which fits upon an ordinary gas-burner. The bar, D, is 30 cm. long, and is pivoted to the thimbie in such a manner that the angle at which it is inclined is indicated on the graduated semicircular plate, E. The burner B can be slid upon the bar so as to be directly behind A or at any distance from it, the distance being shown by the scale marked on the bar (divided on one side into spaces of 2'5 em., and on the other into English inches and half-inches. In determining the degree of ametropia, the jets are lighted and turned down to show small points of flame, about 5 mm. in diameter, and the patient, whose accommodation has been paralyzed with atropine, is placed at a THOMSON’S A METRO METER. distance of about 5 metres. An emmetrope should see each light clearly until one is placed directly behind the other—not as a diffused circle of light, as is the case with a me tropes. The distance to which it is nece ary to separate the lights For both to be seen clearly shows the degree of emetnopies each space of 25 cm. on the bar indicating an ametropia of 1 diopter. The form of ametropia is ascertained by placing a plece of red gla before the eye, SO as to color one half of each circle, and noting on which side the colored half appears to be: if it is on the same side as the gla , there is myopia; if on the opposite side, hypermetropia. To detect astigmatism, the patient should be asked to observe if the flames, sufficiently separated not to coalesce, seem longer in one diameter than in another; if they do, the bar is to be raised or lowered until the two appear to be alike. The pointer, F, will indicate the angle at which oy are yale and the position of the meridian of greatest ametropia. [W. Thomson, “Trans. of the Am. Ophth. Soc.,” 1878, p. 455 (F; L).], AMETRON (Lat.), n. n. A?m(a$m)-e%t/rom, A plant mentioned by Dioscorides, believed to be a Rubus. (Bory (B, 121).] AMETROPE, n. _ 'e?-trop. Fr.,amétrope. Ger., Ametrop. A person affected with ametropia (q. v.). AMETROPTA (Lat.), n. f. ’pi2-a%, From âpezpos, beyond the (normal) limit. and dius, sight. Fr., amétropie, Ger., A metro pie. It.. Sp.. ametropia. Syn.: ecmetropia. A generi = including all defects of vision due to errors of refraction. AMETROPIC, adj. ‘i2k. Fr., amétrope. Ger. ametropisch. Affected with anion (qv). a ö A METRO US, adj. Alm-e?2t’ru®, From a riv., and ppa,the utorus.. Without a uferus. [De 90] 2 d