Macular electroretinogram as a function of age of subjects

Macular and paramacular electroretinograms in response to two adjacent checks (6 deg/side), alternating at constant mean luminance, were recorded in 34 normal subjects ranging in age from 16 to 74 years. The macular electroretinogram declines progressively in amplitude with age (R = –0.42; P = 0.013). The amplitude ratio between macular and paramacular responses tends to be independent of age (R = -0.21; P = 0.22).Age-related changes in the macular electroretinogram shown in our study are consistent with previous anatomical and functional studies, which indicate a deterioration of photoreceptors beyond 20 years of age. These results suggest a possible use of this technique for future studies on macular degeneration.     

Assessment of MRI criteria for abnormal brain MRI in acute monosymptomatic optic neuritis. Comparison to findings in healthy persons

To evaluate various MRI criteria we studied a representative group of 149 consecutive patients below 50 years with acute monosymptomatic optic neuritis (AMON), a frequent first manifestation of multiple sclerosis (MS). The presence, number, size, and localization of areas of increased signal (AIS) on T₂-weighted brain MRIs obtained at 1.5 T were described and compared with findings in 71 healthy persons aged 21–50 years without diabetes, cerebrovascular or neurologic diseases. MRI was performed within 2–145 days, median 16 days from onset of AMON and showed from 0 to 26 AIS, sized 2–30 mm, in 79 of 149 (53%) patients compared to 0–18 AIS, sized 2–12 mm, in 31 of 71 (44%) healthy persons. In patients, AIS were significantly more frequent in women than in men (χ² = 4.67, p > 0.05). Periventricular AIS were revealed in 70 (47%) patients and in 14 (20%) healthy persons. Subcortical AIS were present in 5 (3%) patients and in 18 (25%) healthy persons. Infratentorial AIS were present in only 3 (2%) patients. The sensitivity and specificity of previously proposed diagnostic MRI criteria for MS were unsatisfactory in our group of patients and have previously only been validated in definite MS. We therefore constructed and tested four new sets of criteria. The set with the best relation between sensitivity (e.g. 41%) and specificity (e.g. 93%) was the following: presence of two or more AIS, of which at least one is periventricular or infratentorial, combined with the absence of subcortical AIS. These criteria are recommended for patients with AMON and might be used in other patients with possible or probable MS.     

Diagnostic imaging of orofacial malformations

Summary Two-dimensional conventional X-rays and computer tomographic imaging systems contribute to the diagnosis and surgical planning of patients with orofacial malformations. The ability to reformat CT scans into three-dimensional osseous and soft tissue surface images has a significant impact on the diagnosis and management of orofacial malformations. Cephalometric evaluation with teleradiography provides precise insight into both the skeletal structures and the soft parts, enabling the radiologist to assess the relationship among the different parts in a given subject, at any given time and in relation to the normal.      

Human smooth pursuit during transient perturbations of predictable and unpredictable target movement

Summary The predictive component of human smooth pursuit was studied by perturbing sinusoidal target motion at unpredictable instants. The disturbances consisted of either a brief period of stabilization of the target on the fovea or a replacement of the sine by a ramp displacement for half a period. To minimize the effects of a possible change of the tracking strategy by the subject the transitions were masked and only the initial part of the response to the disturbance was analyzed. After stabilization on the fovea the eye oscillation continued at the frequency of the preceding target movement for about one half-cycle, whereupon the oscillation was rapidly damped. The mean unidirectional smooth eye acceleration was 70% of the mean unidirectional target acceleration prior to the stabilization. This suggests that during pursuit of a sinusoidal target movement about 75% of the oculomotor response is generated by predictive processes. When the sine was replaced by a ramp, starting at the velocity zero-crossing, the eye accelerated away from the target for ca. 180 ms irrespective of the frequency of prior tracking. In contrast, when the ramp started at the peak velocity of the sinusoidal target motion the eye accelerated away from the target for more than a quarter period. After foveal stabilization during pursuit of a pseudorandom stimulus, the eye continued to oscillate for less than one period at approximately the highest frequency present in the stimulus. The frequency characteristics of human smooth pursuit of predictable as well as unpredictable target motion were correctly simulated by a model, which derived its predictive properties from a lead element, tuned to the current frequency of the target motion.     

Multidimensional Chromatographic and Hyphenated Techniques for Hydrophilic Copolymers, 1

Summary: The chromatographic analysis of hydrophilic copolymers is complicated due to the fact that in most cases aqueous eluents must be used. In aqueous eluents different polar and ionic effects may disturb the selective interactions between the macromolecules and the stationary phase making it impossible to separate such copolymers with regard to chemical composition. Therefore, 2D chromatography combining a separation according to composition with a separation according to molar mass has been applied mostly to polymers that are soluble in organic solvents. The present contribution describes experimental approaches to analyze such hydrophilic copolymers by 2D‐chromatography. For a model polymer system resulting from the copolymerization of methacrylic acid and a poly(ethylene glycol) macromonomer, it is shown that different analytical techniques including SEC, LC‐CC, MALDI‐TOF MS and 2D chromatography can be used to analyze the different parameters of molecular heterogeneity of such copolymers.

2D separation of poly(MPEG‐MM 2), 1^st dimension: LC‐CC, 2^nd dimension: SEC.