Refractive changes during 72-hour exposure to high altitude after refractive surgery.

PURPOSE: The authors prospectively analyzed refractive and pachymetric parameters during exposure to high altitude after radial keratotomy (RK) and photorefractive keratectomy (PRK). METHODS: The authors measured manifest and cycloplegic refraction, keratometry, computed video keratography, and central and peripheral pachymetry in six subjects who have undergone RK (11 eyes), six who have undergone PRK (12 eyes), and nine with myopia (17 eyes) at sea level and on three consecutive days at 14,100 feet. All measurements were repeated 1 week after subjects returned to sea level. RESULTS: Subjects who have undergone RK demonstrated a significant and progressive increase in spherical equivalence (+0.30 +/- 0.50 diopters on day 1 and +1.52 +/- 1.01 diopters on day 3; P < 0.001) and a decrease in keratometry values during exposure to altitude when compared with control subjects with myopia. Healthy subjects and those who have had PRK demonstrated no significant change in refractive error. Pachymetry measurements demonstrated significant peripheral corneal thickening in all three groups (RK, P < 0.004; PRK, P < 0.007; control subjects, P = 0.0006) by day 3 at high altitude. Refraction, keratometry, and pachymetry returned to baseline (P = 1.000) after return to sea level. CONCLUSIONS: Seventy-two-hour exposure to high altitude in subjects who have had RK induces a significant, progressive, and reversible hyperopic shift in refraction with corresponding video keratographic and keratometric changes. The authors hypothesize that the high-altitude hypoxic environment causes increased corneal hydration in the area of the RK incisions, which may lead to central corneal flattening and a hyperopic shift in refractive error. Subjects who have had PRK and those with myopia are not susceptible to this refractive shift. The authors' RK data suggest that the time since surgery and the amount of surgery are related to the degree of hyperopic shift during altitude exposure.

Effect of sheep breed and sex on accumulation and depletion of ronnel in fat.

When four breeds of sheep were dipped in .25% ronnel for control of sheep-biting lice, Bovicola ovis (Schrank), the differences in residues in the fat were highly significant for breed, sex, day X breed and day X sex interactions.

Distribution and depletion of radioactivity in hens treated dermally with 14C-labeled permethrin.

The 25/75 cis-trans mixture of permethrin (BW21Z), one of the new broad-spectrum pyrethroid insecticides, was labeled with 14C in the alcohol methylene carbon moiety and mist sprayed at two rates (3.77 or 11.94 mg/hen) on 28 hens. Peak permethrin equivalents in both treatment groups were found in the skins, .414 and l.69 ppm, respectively. Total permethrin equivalents peaked 3 days after treatment, but permethrin equivalents in eggs peaked 5 days after treatment.

Simultaneous determinations of azinphos ethyl, azinphos methyl and its oxygen analog by gas liquid chromatography.

A simple gas liquid chromatographic method for simultaneous determinations of azinphos methyl, the ethyl homolog, and the oxygen analog is described. The procedure can detect, quantitatively by gas chromatography, azinphos methyl and the ethyl homolog residues in milk at 0.038 ppm. The oxygen analog can be detected and quantitated at 0.06 ppm.

Effects of a herbicide, 2-ethyl hexyl ester of 2,4-D on magnesium: Calcium ratios and blood urea nitrogen levels in sheep and cattle.

The herbicide, 2,4-Dichlorophenoxyacetic acid, 2-ethyl hexyl ester (Weed Rhap(R)), produced a decrease in plasma calcium and increase in plasma magnesium, giving a significant ratio change in the plasma of the 2 sheep and yearling heifer that died. Each of these had increased blood urea nitrogen (BUN) levels, and the pathological examinations at necropsy showed kidney damage and swollen, blood-engorged thyroids. The formulation of the dose in sheep either as emulsifiable concentrate (EC) or as technical material, showed no effect difference.