An exploration of modified monovision with diffractive bifocal contact lenses.

A group of eight presbyopic subjects wore in succession four types of correction. One of these (A) consisted of a conventional pair of diffractive bifocals in which equal amounts of light contributed to the distance and near images in both eyes. Two (B and C) were modified monovision corrections using non-standard diffractive bifocal lenses. The diffractive designs were such that in the dominant eye a greater fraction of light was sent into the distance image and less into the near image and in the non-dominant eye a greater fraction contributed to the near image. The last lens combination (D) was a conventional monovision arrangement, with a single-vision distance correction on the dominant eye and a single-vision near correction on the non-dominant eye. Monocular and binocular high-contrast acuity, contrast sensitivity and stereopsis were assessed at both distance and near with each of the four lens combinations. It was hoped that the modified monovision arrangements (B and C) might yield improved distance and near acuities in comparison with the standard diffractive bifocals (A) while still maintaining good stereopsis in comparison with the single-vision monovision combination (D) and thus allow wearers to achieve better all round visual performance. Although these expectations were at least partly fulfilled, the modest advantages offered by the diffractive modified monovision approach did not appear to compensate for the disadvantages of its greater complexity.

Analysis of taste mixtures by adults and children.

Children at mid-childhood (8-9 years), have limited perceptual-attentional skills to analyze complex stimuli (Shepp, Barrett, & Kolbet, 1987), and little is known of their skills to analyze chemosensory stimuli. Accordingly, this study investigated the ability of adults and 8-9 year old children to perceive tastes in binary mixtures. In Experiment 1, subjects used a selective attention procedure to indicate whether sweet, salty, and sour tastes were present in stimuli consisting of sucrose (sweet), sodium chloride (salty), citric acid (sour), and all possible binary mixtures of these tastants. Adults correctly recognized the two tastes in all mixtures, whilst children recognized only one in each mixture. Children were successful in recognizing sweet in both sweet-containing mixtures and salty in the sodium chloride-citric acid mixture. In Experiment 2, subjects used a similar selective attention paradigm to assess the perceived intensity of the three tastes in the above single and two-component stimuli. Suppression of one or both components was recorded with most mixtures by both age groups. However, with the mixture sodium chloride-citric acid, only the children recorded suppression of sourness, whilst for adults only saltiness was suppressed. In neither mixture containing sourness did children report suppression of sweetness or saltiness. It is concluded that at mid-childhood humans have difficulty analyzing taste mixtures into their components, due to attentional and possibly gustatory shortcomings.

Diffractive bifocal contact lenses in aphakia and pseudophakia. A pilot study.

Diffractive bifocal contact lenses function by diverting incident light to two focal points. Light from near objects is focused by diffraction while that from distant objects is focused by conventional refraction. Both processes occur simultaneously throughout the full aperture of the lens. Fourteen aphakic and pseudophakic contact lens wearers were fitted with diffractive bifocal lenses and observed for an eight week period. Six (42.8%) were satisfied with the visual result. Five subjects (35.7%) discontinued lens wear complaining of poor quality of near vision. We conclude that these lenses may help selected aphakic patients to discard their reading glasses but the low acceptance rate suggests that this type of optic is probably not suitable for implantation as an intraocular lens.

A comparison of the cytological effects of three hypoxic cell radiosensitizers.

Misonidazole has entered Phase III clinical trials as a hypoxic cell radiosensitizer. Neurotoxocity is the major dose-limiting factor and has prompted the development of two further compounds with reduced lipophilicity and shorter half-life in vivo. Aside from the short-term problem of neurotoxocity, other potential long-term consequences should be considered. Such is the purpose of this investigation where the cytological effects of three radiosensitizers upon oxic and hypoxic Chinese hamster V-79 cells have been examined. Two newer compounds, desmethylmisonidazole and Stanford Research compound 2508, were compared with their clinically used predecessor, misonidazole. Under aerated conditions, cell killing was increased with SR-2508 in a concentration and time dependent manner, so as to exceed by more than three times the level produced by the other two drugs at 5 mM for 72 hours. Cell progression into mitosis was also markedly reduced by as much as 1/10,000 of control values. However, as the three compounds induced similar frequencies of sister chromatid exchange (SCE) and chromosome aberration, the enhanced cytotoxic effect of SR-2508 appears to be mediated via an interphase rather than a post-mitotic cell death. Cells were made hypoxic and treated with the three drugs for 4 hr, then mitoses sequentially collected for 16 hr. The three compounds produced similar levels of cell killing, slowing of cell cycle progression, SCE's and chromosome aberrations, with cycle-specific effect on S and G-1 phase cells for SCE induction. These results indicate that desmethylmisonidazole and misonidazole have similar cytotoxic and clastogenic properties under oxic and hypoxic conditions. SR-2508 is relatively more toxic to aerated cells and may deserve close clinical observation for toxicity to normal tissues; further, all three agents may enhance DNA damage and mutagenesis in tissues that are normally hypoxic.

Effects of long contact times of misonidazole on attached Chinese hamster V79 cells.

The 2-nitroimidazole misonidazole, an hypoxic cell radiation sensitizer, has been shown to be cytotoxic to attached oxic Chinese hamster V79 cells after high doses and long contact times. This killing effect is enhanced if BrdU is incorporated into chromosomes. It was found that misonidazole slows cell progression through the cell cycle and that those cells that move into mitosis carry very few chromosomal aberrations suggesting that the majority of cells are dying in interphase. The level of induced SCEs both in 2nd and 3rd division cells was comparatively slight; being always less than twice the control level although there was an indication of an increased incidence with dose. Since human exposure to misonidazole will only be at low concentrations, these results imply that misonidazole is a comparatively safe agent, particularly when its effect are contrasted with those of other chemotherapeutic agents.

Postoperative alterations in size of Dacron aortic grafts: an ultrasonic evaluation.

Reports of aneurysmal dilatation involving Dacron aortic prostheses have raised questions concerning the incidence, degree and significance of postoperative alterations in graft size. Consequently, a study was undertaken to evaluate Dacron graft size by ultrasooud in 95 asymptomatic patients selected at random after aortic surgery. A Vidison Real Time ultrasound unit was used to determine the internal diameter of the aortic portion of the various grafts utilized: 41 Cooley knitted, 25 Vasculour-D; 13 U.S.C.I. ultralightweight; nine Wesolowski Weavenit; and seven DeBakey standard weight knitted. Patients were studied at from two weeks to 138 months postoperatively (average of 33 months). Hypertension was present in 64% of patients. In the total series, the degree of mean dilatation was 17.6%. Average dilatation in patients with normotension was 15% compared to 21% in hypertensive patients. Graphic analysis of the data collected indicated that dilatation of a significant degree occurs in the immediate postoperative period and slowly increases with time; the time regression period and slowly increases with time; the time regression lines for normotensive and hypertensive patients were almost parallel. Results of this clinical study appear to corroborate the results of in vitro quality control tests performed by two graft manufacturers (Meadox and U.S.C.I.).

Focal splenic defects.

Review of more than 2,000 liver-spleen scans revealed 18 cases of focal splenic defects. Three major categories are defined: lymphoma, infarctions, and metastatic tumor. Clinical presentation is important in determining the precise etiology, and a differential diagnosis is presented. It appears that: (a) reticulum cell carcinoma is as likely to cause defects as is Hodgkin's disease; (b) splenic infarction is related to pancreatic disease through the splenic vein; and (c) malignant melanoma is the most common secondary deposit as detected by scanning.

Manifestations of hypertrophic pulmonary osteoarthropathy in patients with carcinoma of the lung. Demonstration by 99mTc-pyrophosphate bone scans.

Two patients with carcinoma of the lung were studied with 99mTc-stannous pyrophosphate. Resolution of scintigraphic activity was observed postoperatively in one patient, while the second patient showed an asymmetric pattern of radionuclide uptake and radiographic changes as well as clinical findings of hypertrophic pulmonary osteoarthropathy.