Endothelial viability of organ-cultured corneas following penetrating keratoplasty.

PURPOSE: To assess endothelial integrity following corneal transplantation using human corneas stored in organ culture in the Manchester Eye Bank. METHODS: A prospective study was undertaken on 24 patients who had received full-thickness corneal grafts using corneas stored in organ culture. The donor corneal endothelium was photographed prior to transplantation using light microscopy. Specular microscopy and ultrasonic pachometry were performed at 30 days (+/- 3 days), 12 weeks (+/- 1 week), 26 weeks (+/- 2 weeks) and 52 weeks (+/- 4 weeks) following corneal transplantation. The following cell parameters were measured: density, area, coefficient of variation (CV) for area, perimeter, diameter, form factor and corneal thickness. RESULTS: One year after corneal transplantation there was a statistically significant decrease in endothelial cell density (-39.4%), and a statistically significant increase in endothelial cell area (+94.4%), perimeter (+36.1%), diameter (+57.1%) and form factor (+5.8%). However, no significant changes were seen in CV or corneal thickness with respect to time after transplantation. (There were no significant changes in endothelial cell parameters and corneal thickness for 12 control subjects.) CONCLUSIONS: Endothelial cell loss occurs at an accelerated rate from corneal transplants. This highlights the need for improving corneal endothelial viability during and after storage in order to improve the chances of longer-term survival of the transplanted cornea.

Diurnal variations in human corneal thickness.

AIM: To elucidate the diurnal variation in human corneal thickness over a 48 hour period. METHOD: Changes in central corneal thickness were monitored in eight healthy subjects (four male, four female) aged between 10 and 63 years using an ultrasonic pachymeter. Measurements were made over a 48 hour period-immediately before sleep, immediately upon waking and at 15, 30, 45 minutes, 1, 1.5, 2, 2.5, 3 hours, and at 2 hour intervals thereafter throughout the remainder of each day. RESULTS: The mean corneal thickness for the group (SD) was 546 (14) microns, with a mean overnight increase of 5.5% (2.9%) (range 1.9-12.6%) and a maximum diurnal increase of 7.2% (2.8%) (range 2.1-14.3%). Individual differences in the extent of diurnal and overnight variation occurred within the group. For three subjects, the first reading taken on waking was not the highest and corneal thickness continued to increase. CONCLUSION: These data confirm an increase of corneal thickness during sleep, but also reveal considerable variation during waking hours. Thus, the overnight changes in corneal thickness are not truly representative of diurnal variations in human corneal thickness and, in fact, much greater diurnal variation occurs than the 3.0-4.4% previously reported.

Rapid accretion and early differentiation of Mars indicated by 142Nd/144Nd in SNC meteorites.

Small differences in the ratio of neodymium-142 to neodymium-144 in early formed mantle reservoirs in planetary bodies are the result of in situ decay of the extinct radionuclide samarium-146 and can be used to constrain early planetary differentiation and therefore the time scale of planetary accretion. The martian meteorite Nakhla (approximately 1.3 billion years old), the type sample of the nakhlite subgroup of the Shergottite-Nakhlite-Chassigny (SNC) meteorites, exhibits a 59 +/- 13 parts per million excess in the ratio of neodymium-142 to neodymium-144 relative to normal neodymium. This anomaly records differentiation in the martian mantle before 4539 million years ago and implies that Mars experienced no giant impacts at any time later than 27 million years after the origin of the solar system.

A randomised study to determine whether routine intravenous magnesium supplements are necessary in patients receiving cisplatin chemotherapy with continuous infusion 5-fluorouracil.

Cisplatin is an effective antineoplastic agent, but can cause renal tubular damage leading to urinary magnesium wasting and hypomagnesaemia. Cisplatin and 5-fluorouracil, when used in combination, have synergistic antitumour activity in upper gastrointestinal malignancies, but it is unclear whether they have additive effects on renal magnesium loss. To determine the optimal regimen for magnesium supplementation in these patients, we have conducted a randomised trial of routine intravenous magnesium supplements compared with magnesium given on an 'as required' basis. 32 patients were randomised to receive magnesium intravenously in prehydration and posthydration fluids with cisplatin chemotherapy, or to receive magnesium only when the serum level was low. 5-fluorouracil was given as a continuous infusion. Serum magnesium was measured on admission for each cycle of chemotherapy and an interim measurement performed between each cycle. 28 patients were evaluable. All patients randomised to receive magnesium on an 'as required' basis had at least one episode of hypomagnesaemia. On subsequent admissions for chemotherapy (cycles 2 and 3), the mean serum magnesium level was significantly lower in these patients compared with patients who received magnesium routinely (P < 0.05). After omission of magnesium from the first cycle of cisplatin, magnesium supplements were necessary in 50% of subsequent cycles, usually by the second or third cycle. Moreover, there were several instances of symptomatic hypomagnesaemia requiring further intravenous supplements in mid-cycle. Patients treated with a combination of cisplatin and 5-fluorouracil should be given intravenous magnesium supplements with each cycle of cisplatin chemotherapy. Nevertheless, episodes of hypomagnesaemia still occur, and additional intravenous supplements may be required, highlighting the importance of measuring this electrolyte.

Attitudes of faculty members of schools of public health toward public service.

Public service has long been considered one of a traditional triad of academic functions--teaching, research, and service. Yet even in schools of public health, where service is purported to be an integral component of the institution's mission, faculty generally do not accord as high a value to service performance or approach it with the same degree of commitment as they do research and teaching. A study was conducted to examine faculty perceptions and attitudes toward the service function and its relationship to teaching and research within schools of public health. The data were taken from a mailed questionnaire survey of 20-30 faculty members in each of 20 schools of public health in the United States. The response rate was 71 percent, or 387 returned questionnaires. Respondents generally felt that the greatest value of service lies in its potential for enhancing the image and prestige of the school, and in the fulfillment of the community obligation of the institution. The possibility that service might bring about improvements in faculty research and teaching, or improvements in health services and public health, was rated significantly lower. Thus, respondents did not view service as useful for its contribution to their own careers or to public health practice as much as they regarded it as a beneficial contribution to the reputation of the institution. This view undermines the traditionally held notion that public service either benefits a particular constituency outside the school or enhances the professional development of faculty members themselves.

Point/counterpoint: declining public health organizations--will management make a difference?

Time is running out for public health organizations, says Charles Harper. Their traditional role in the health system is eroding rapidly. To reestablish the place they deserve in the health system will require an aggressive and united effort on the part of all public health professionals. As a counterpoint to Harper's article, Donald Smith asserts that the decline is a result more of a negative image and changing standards than of managerial problems.

Nitrogen fixation in some anoxic lacustrine environments.

Low rates of acetylene reduction to ethylene in water samples from two dystrophic lakes indicate the presence of nitrogenase and in situ nitrogen fixation. Highest rates were found in anoxic water from the aphotic zone. Environmental conditions in these lakes suggest the agents of fixation were bacteria.