se (l) a he high- the low- "acaptn -ietrle 17 nticular ed than ferences 2 higher out (see the lens e argues me post retween aee er lens exrwn the gm ee te Aerriam ‘nificant obvious wing the retween an ap- nonexposed animals (increasing with age) but have been found in significantly greater numbers in mice exposed to even very low doses of radiation.?° ividuals Methods lens will adiation Slit-lamp microscopic examination after iris dilatation with tropicamide 0.5% (Mydriacyl) was made of people within the several exposure groups as follows: 175 rads (midline gammadoseinair), may be g an in- ate), (2) 1 (3) the ion. For ‘latively nination ���ourse of an adevering a ividuals bers (for € groups L this ex- status of ige, and in these 15 years ul survey discrete capsular t can be nin the ich may igle lens resent in Figure 17. Photographsof the optic lens taken through the slit-lamp microscope at 312 magnification and en- larged 24% x. Lensflecks are visible in and to the right of the light arc which lies at the left in each photograph, created by impingementof the lamp beam onthe lens posterior capsule. Left: Mouse, nonirradiated, one year old. Right: Human,a 39-year-old Marshall Island female exposed to 175 rads offallout radiation 15 years previously. 41 persons; 70 rads, 10 persons; 14 rads, 15 per- sons; nonexposed, 80 persons. The observer was unaware of the group to which each individual belonged until after the examinations, First a brief general inspection (at a magnification of 200 or 312) was madeof the cornea, aqueous humor, lens, and anterior vitreous humor. Representative photographsweretaken, usually at 312 x. Finally counts were made of minute discrete opacities (flecks) falling within the 2.5-mm-diametercircle projected into the viewedfield by an ocular reticle. Counts were madewithin the anterior andposterior subcapsularregions ofeachlens at a location about one-half lens radius below the midline. This location was selected to minimize the corneallight reflex as the narrowslit-lamp beam was sweptacross the counting region. Axial traverse of the focus during counting gave depth to the counting area, effectively creating a cylinder of 2.5-mm diameter and extending between the lens capsule and lens nucleus. Eight egos were unsatisfactory because of advanced a comeal defects. cataracts, lens extractions, or SogazZ 74 . Figure 18. Electron micrograph ofoptic lens fibers of a 21-week-old mouse exposed to 3000 rads of Co gamma rays at 6 weeks of age. Thefibers are seen in cross section, and a defective fiber lies near the centerof thefield. (From H.A. Johnson, Acta Iberica Radtol. Cancerol, 19: 247-54, 1964).