Effects of luminance, contrast, and blur on visual acuity

Although previous investigations have reported that changes in background luminance, stimulus contrast, and dioptric blur can each affect visual acuity independently, it has not been shown how these three variables interact to influence visual acuity. This is a particularly important issue if one is interested in predicting how individuals with different refractive characteristics will be able to perform acuity-based tasks in degraded visual environments with low background lighting and contrast levels. To investigate these relations, we conducted a series of experiments in which measurements of visual acuity were obtained for four subjects using Landolt C targets of varying contrast at several background luminances for levels of blur between 0 and 8 diopters (D). Our results show that visual acuity is significantly affected by all three factors, and that their effects are essentially additive. At all luminance and contrast levels, the reduction in visual acuity is greatest for dioptric blur up to 2.0 D, with a more gradual reduction in visual acuity for dioptric blur of greater than 2.0 D. At all blur and luminance levels, visual acuity decreases gradually for contrast levels down to 20%, and decreases sharply for lower contrast levels. Over the range of background luminances we tested (75.0 to 0.075 cd/m2), visual acuity decreases linearly with reductions in luminance. The additive effects of dioptric blur, contrast, and luminance provide a basis for predicting visual acuity-related task performance for individuals in different visual environments. For example, an individual with 6/6 (20/20) visual acuity under high luminance-high contrast conditions will fall to 6/18 (20/60) acuity for low luminance conditions and 6/30 (20/100) for low luminance-low contrast conditions. Similarly, an individual with an uncorrected visual acuity of 6/30 (20/100) under optimal conditions will fall to approximately 6/120 (20/400) under low luminance conditions and 6/240 (20/800) under low luminance-low contrast conditions.     

Detection of neutral hydrogen atoms in a fusion plasma

A two photon excitation scheme for detection of neutral hydrogen atoms in a fusion plasma is described. The approach has the advantages of both the Lyman and Balmer scattering methods presently being used. Further, it is shown that existing laser technology produces the required laser power.     

Recording eye movements using coaxial cameras--applications for visual ergonomics and reading studies

We developed a system of coaxial video cameras that records monocular eye position and scene, and superimposes these images using a digital video mixer. We mounted miniature video cameras above and below a cube beam-splitting prism in the spectacle plane. An infrared emitting diode was imaged in the cornea to locate eye position. The technique was accurate to about 0.5 degrees within 15 degrees of primary gaze; however, we see its main advantages as being its low cost and simple design that, for some applications, does not require complex computer analysis and data manipulation. With improved camera optics, it has the potential for helmet mounting and use remote from a recording console. We used the instrument to monitor a reader's eye position when using low vision devices, and see applications of the technique in the field of visual ergonomics and sports vision.     

Fluorometric assessments of acrosomal integrity and viability in cryopreserved bovine spermatozoa

It is widely agreed that after two or more seizures patients should be given antiepileptic treatment, but there is still controversy about the treatment of patients after a first unprovoked seizure. In a multicenter, randomized, open trial, patients with a first tonic-clonic seizure were randomized to immediate treatment (carbamazepine, phenytoin, phenobarbital, or sodium valproate) or to treatment only after another seizure. Fifty-two (24%) of the 215 patients randomized to immediate treatment and 85 (42%) of the 204 randomized to delayed treatment experienced seizure recurrence during follow-up. Age, acute treatment of the seizure with benzodiazepines, remote etiologic factors, and EEG abnormalities were significant predictors of relapse. Of the immediately treated patients, 87% had no seizures for a year and 68% had no seizures for 2 years, whereas only slightly fewer initially untreated patients (83% and 60%) achieved these endpoints. Patients treated after the first seizure and those treated after seizure relapse had the same time-dependent probability of achieving 1 and 2 seizure-free years. None of the variables that were prognostic predictors of relapse was significantly associated with the probability of having 1 or 2 years of seizure control. Anticonvulsants in patients presenting a first tonic-clonic seizure reduce the risk of relapse; however, 50% of patients who are not treated will never experience a second seizure. Moreover, the probability of long-term remission is not influenced by treatment of the first seizure.     

Ethanol effects on synaptic neurotransmission and tetanus-induced synaptic plasticity in hippocampal slices of chronic in vivo lead-exposed adult rats

The interaction of chronic in vivo lead exposure and acute in vitro ethanol treatment on synaptic neurotransmission and plasticity were studied using extracellular electrophysiological techniques in CA1 region of hippocampal brain slices from adult rats. Neither chronic lead exposure nor acute ethanol treatment had any significant effect on field excitatory postsynaptic potentials (EPSPs). In vivo lead exposure enhanced short-term potentiation (STP, potentiation that decays within 30 min) by 21% shortly after 'weak' tetanus, but had no effect on long-term potentiation (LTP, sustained at least 1 h). In vitro bath application of 60 mM ethanol inhibited STP by 35% and blocked LTP induced by 'weak' tetanus in slices from Pb exposed rats (500 ppm lead acetate, 56-70 days), while having no effect on STP or LTP in slices from control counterpart Na-exposed rats (pair-fed 216 ppm sodium acetate). In contrast, 'strong'-tetanus-induced LTP was abolished in Pb-exposed slices, and 60 mM ethanol slightly inhibited STP and blocked LTP in slices from Na-exposed rats. These differences could not be explained by differences in ethanol inhibition of NMDA-mediated field EPSPs because they were similarly reduced in slices from Na-exposed (30%) and Pb-exposed (25%) rats. These findings suggest that the strength of the tetanus used determines whether or not synaptic plasticity is blocked by either chronic lead exposure or acute ethanol treatment, and that even in adult rats, hippocampal synaptic LTP can be compromised by combined exposure to ethanol and lead. More importantly, these findings suggest the consequences of combined lead exposure and alcohol abuse in the adult human population may not be fully recognized yet.     

Review of the organized support network for infertility patients in licensed units in the UK

In acknowledging that 'counselling is generally recognized as beneficial', the Human Fertilization and Embryology Authority (HFEA) Code of Practice requires that all infertility units provide counselling facilities to be available for patients. In this study, we intended to evaluate the support and counselling services made available by the licensed units in the UK. A questionnaire consisting of 30 questions was designed and sent to every licensed treatment unit in the UK. The data were coded on a nominal scale and, using a data entry program, loaded onto a computer. Using the Statistical Package for the Social Sciences program, a non-parametric frequency analysis was performed. Associations were examined with cross-tabulations and chi 2 analysis. A total of 62 units (61.4%) responded to the questionnaire, from both the private and National Health Service sectors. Of these, 95% have their own counsellor, most of whom (84%) practised on the premises. One-third of these counsellors had a dual role, mainly as nurses, social workers or in administration; 98.6% were trained in counselling, with only 28% having either the Certificate or Diploma in Counselling. One-third (32.2%) of centres charged for counselling, with only 13 units indicating their charges. The majority of centres (78.8%) do not actively follow-up patients after counselling and one-quarter (25.5%) did not have a specific counselling room. Over two-thirds (68.4%) of centres described their support network as adequate. The results of this survey suggest that, although the requirements of the HFEA Code of Practice are being adhered to reasonably well, overall patient uptake of counselling is low.(ABSTRACT TRUNCATED AT 250 WORDS)