Is the spectacle lens jack‐in‐the‐box phenomenon really due to the lenses?

The calculation of the extent of the ring scotoma around positive lenses, as conventionally taught to students of clinical optics, indicates that the scotoma is of a significant size. Using knife-edge lenses this study shows that the calculations are invalid due to the finite size of the eye's entrance pupil and in many instances the scotoma is shown not to exist. The effect noticed in clinical practice is probably largely due to the frame and the edging techniques used which add to the refractive scotoma which is present with high powered lenses, large apertures and/or small pupil sizes.     

Pharmacokinetics of the 13C labeled anticancer agent temozolomide detected in vivo by selective cross-polarization transfer

The anticancer agent temozolomide labeled with ¹³C (8-Carbamoyl-3-13C-methylimidazo-[5,1-d]-1,2,3,5-tetrazin-4-(3H)-one), was noninvasively detected in subcutaneous RIF-1 tumors by a selective cross polarization ¹³C NMR method, at a field strength of 9.4T. Pharmacokinetics of the drug, at a dose of 150 mg/kg, were determined for intravenous and intraperitoneal modes of administration (three animals per mode). The half-life of the drug in the tumors was approximately 60 min. The uptake and clearance of the drug, however, varied significantly between individual hosts, for both modes of administration. These results demonstrate the feasibility of obtaining pharmacokinetics of anticancer agents for individual tumors without the need for a label that might modify drug activity (e.g., fluorine). The variability of the in vivo measurements, even within the same tumor model, demonstrates the necessity of directly monitoring the tumor to evaluate drug pharmacokinetics.     

A preliminary statistical model for identifying repeaters of parasuicide

This paper presents a statistical model constructed using logisticregression to identify those at high-risk of repeating parasuicide. Thesubjects in the study are Cork city residents who exhibited parasuicidalbehaviour between 1 January and 30 June 1995. Repetition of the behaviourwithin six months of the index episode distinguishes repeaters fromnon-repeaters. The model was designed so that it could be used bynon-clinicians and hence does not require information relating topsychiatric diagnosis or use of psychiatric services. The proportion ofsubjects correctly classified remained stable across a range of cut-pointprobabilities (mean = 86%, range: 83.9–87.5%). Using acut-point of 0.2, 96% of repeaters and 81% of non-repeaters were correctly classified. Using 0.45 led to the correct identification of81% of repeaters and 90% of non-repeaters. If these highlevels of sensitivity and specificity are maintained in validation tests onfuture cohorts in Cork city then the model could form the basis of anintervention programme designed to prevent the repetition of parasuicide.     

Cardiovascular collapse during anesthesia in a patient with preoperatively discontinued chronic MAO inhibitor therapy

We describe a patient in whom long-term monoamine oxidase (MAO) inhibitor therapy was discontinued 20 days before surgery with general anesthesia. This patient developed severe perioperative hypotension after administration of 10 mg of bupivacaine through an epidural catheter, which was corrected only after potent vasopressor therapy. We attribute this hemodynamic instability to attenuation of this patient's sympathetic tone based on several mechanisms: (1) residual effect of long-term administration of MAO inhibitor that caused a decrease in the number of β-adrenergic receptors (adrenergic subsensitivity due to receptor down-regulation), (2) recovered MAO activity causing effective degradation of sympathetic amines, and (3) combined attenuating effects of general and epidural anesthesia on sympathetic tone.     

Interactions of retinoic acid and androgens in human prostatic tissue.

The effect of retinoic acid (RA) on testosterone metabolic pathway was investigated in hyperplastic and neoplastic human prostatic tissues, and also the effects of steroids on RA binding to its receptor. Steroids only had a minimal effect on the binding of RA by its receptor. The conversion of testosterone to DHT by 5 alpha-reductase was reduced in the presence of retinoic acid. The inhibition was probably due to competition with NADPH for enzyme binding sites. The degree of inhibition found with retinoic acid at a concentration of 10(-4)M was greater for hyperplastic (41%) than that for neoplastic tissue (24%). The inhibition of 5 alpha-reductase by retinoic acid was dose-dependent. The activity of 5 alpha-reductase is significantly less in neoplastic compared with hyperplastic tissue.     

A model of waveform reliability in facial nerve electroneurography

This study identifies four factors that should be considered when evaluating the reliability of new testing methods in facial nerve electroneurography (ENOG): (1) waveform peak-to-peak amplitude; (2) response variability; (3) statistical significance of day-to-day test/retest differences; and (4) waveform morphology. These factors were applied to data gathered on seven normal subjects who had three trials of facial-nerve ENOG on three separate test days in order to determine an optimal recording electrode montage. Both bipolar and monopolar recording-electrode montages were used on the nasal alae and on the nasolabial crease. Resultant peak-to-peak amplitudes of combined motor action potentials were recorded and measured using a clinical evoked-potential instrument. A biphasic waveform shape with optimal peak-to-peak point rather than the nasolabial crease. The contribution to the assessment of response reliability of each of the four factors is discussed.