Correcting ocular spherical aberration with soft contact lenses

Following aberroscopy, aspheric front surface soft contact lenses (SCLs) were custom-made to correct spherical refractive error and ocular spherical aberration (SA) of 18 myopic and five hypermetropic subjects (age, 20.5 +/- 5 yr). On-eye residual aberrations, logMAR visual acuity, and contrast sensitivity were compared with the best-correcting spectacle lens, an equally powered standard SCL, and an SCL designed to be aberration free in air. Custom-made and spherical SCLs reduced SA (p < 0.001; p < 0.05) but did not change total root-mean-square (rms) wave-front aberration (WFA). Aberration-free SCLs increased SA (p < 0.05), coma (p < 0.05), and total rms WFA. Visual acuity remained unchanged with any of the SCL types compared with the spectacle lens correction. Contrast sensitivity at 6 cycles/degree improved with the custom-made SCLs (p < 0.05). Increased coma with aspheric lens designs and uncorrected astigmatism limit the small possible visual benefit from correcting ocular SA with SCLs.     

A critical evaluation of the strategy project

The STRATEGY project (sustainable restoration and long-term management of contaminated rural, urban and industrial ecosystems; www.strategy-ec.org.uk) addressed the need for a holistic decision framework for the selection of optimal remediation strategies for long-term sustainable management of contaminated areas in Western Europe. The project considered both technical and social aspects of implementing restoration strategies for urban and rural environments. The importance of considering socially relevant objectives in addition to the dose reduction was emphasised. A critical evaluation was carried out on 101 selected countermeasures, (including rural waste disposal options), a model was developed to aid optimising countermeasure strategies and a method of carrying out participatory decision-making suggested. The outputs of the project are described and critically evaluated.     

Hemodynamic responses to stellate ganglion stimulation in mongrels and greyhounds

A comparison of the effects of left stellate ganglion stimulation (SGS) on central and aortic hemodynamics has been made in chloralose-anesthetized mongrel (M), and greyhound (GH) dogs. Measurements of aortic pressure and flow, and left ventricular pressure were made during stimulation of the decentralized left SG at different frequencies from 0 to 20 Hz. The increases in aortic pressure and flow with SGS were larger in the GH, especially for low frequencies of stimulation. Stroke volume was increased with SGS in the GH at all stimulation rates, whereas in the M it was unchanged. A greater decrease in left ventricular end-diastolic pressure with SGS was found in the GH. These results suggest that differences exist in both the intrinsic and extrinsic control of cardiac output in the greyhound dog compared to the mongrel. These differences may be in part responsible for the elevated arterial blood pressure in the greyhound compared to the mongrel.     

Phase and amplitude dispersion for Earth-satellite propagation in the 20- to 30-GHz frequency range

Amplitude and phase dispersion have been measured for over a year on a 19- and 28-GHz earth-space propagation path. In the experiment amplitude and phase differences were compared for a 28-GHz carrier withpm264-MHz sidebands and a 19-GHz carrier, all transmitted from a COMSTAR satellite. No dispersion (frequency selective fading) was found of the type caused by multipath propagation with a large spread in time delay or by resonances in the propagation medium. The only frequency dependences evident were due to the bulk properties of water in rain. The conclusion from this investigation is that amplitude and phase dispersion should not pose a problem for wideband (on the order of 1 GHz) satellite communication systems operating at frequencies greater than 10 GHz with elevation angles from the earth terminals of greater than15deg.     

Getter sputtering—a review

The historical background and current use of getter sputtering are reviewed and it is shown that the process often occured in early apparatus because of fortuitous layout of the chamber components. Getter systems are classified into “static” and “ynamic” according to the gas flow and pumping conditions. In conclusion mass spectra are given of the gas atmospheres in an r.f. getter sputtering plant when depositing tantalum. It is shown that gettering reduces the gaseous impurities. However, provision of the extra getter target requires use of increased power input. Otherwise the deposition rate can fall (from an overall reduction in ion current density) which increases in the desired coating the proportion of sorbed impurity from gas released in the substrate coating vessel.     

Effects of 2,2'-dipyridyl and related compounds on platelet prostaglandin synthesis and platelet function

2,2'-dipyridyl, a chelator of ferrous iron and inhibitor of platelet aggregation, was studied together with several similar compounds to determine the mechanism of their effects on platelets. All of these compounds were more potent inhibitors of arachidonic-acid-mediated aggregation (IC50, 0.17-1.8 mM) than of ADP-mediated aggregation (IC50, 7.6-19.7 mM). At low concentrations required to inhibit arachidonic-acid-mediated aggregation, 2,2'-dipyridyl, 4,4'-dipyridyl and 2-chloropyridine specifically inhibited the platelet cyclo-oxygenase. The mechanism of inhibition of ADP-induced aggregation was investigated, but was not explained. At concentrations needed to inhibit ADP-induced aggregation, 2,2'-dipyridyl did not alter cell ultrastructure, serotonin or nucleotide content or interfere with release of [14C]arachidonic acid or calcium movements. Therefore, our results indicate that 2,2'-dipyridyl and related compounds have two effects on platelets, both due to the unprotonated form. The inhibition of cyclo-oxygenase by low concentrations of these compounds is not due to bidentate iron chelation, since 4,4'-dipyridyl was almost as effective as 2,2'-dipyridyl, but is compatible with binding of these inhibitors to the iron in the heme of the cyclo-oxygenase.     

Effect of rotation and translation on the expected benefit of an ideal method to correct the eye's higher-order aberrations

An ideal correcting method, such as a customized contact lens, laser refractive surgery, or adaptive optics, that corrects higher-order aberrations as well as defocus and astigmatism could improve vision. The benefit achieved with this ideal method will be limited by decentration. To estimate the significance of this potential limitation we studied the effect on image quality expected when an ideal correcting method translates or rotates with respect to the eye's pupil. Actual wave aberrations were obtained from ten human eyes for a 7.3-mm pupil with a Shack-Hartmann sensor. We computed the residual aberrations that appear as a result of translation or rotation of an otherwise ideal correction. The model is valid for adaptive optics, contact lenses, and phase plates, but it constitutes only a first approximation to the laser refractive surgery case where tissue removal occurs. Calculations suggest that the typical decentrations will reduce only slightly the optical benefits expected from an ideal correcting method. For typical decentrations the ideal correcting method offers a benefit in modulation 2-4 times higher (1.5-2 times in white light) than with a standard correction of defocus and astigmatism. We obtained analytical expressions that show the impact of translation and rotation on individual Zernike terms. These calculations also reveal which aberrations are most beneficial to correct. We provided practical rules to implement a selective correction depending on the amount of decentration. An experimental study was performed with an aberrated artificial eye corrected with an adaptive optics system, validating the theoretical predictions. The results in a keratoconic subject, also corrected with adaptive optics, showed that important benefits are obtained despite decentrations in highly aberrated eyes.