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Biomedical subjects

M Alpern

Publications and source records attributed to M Alpern.

At least 19 recordsLinked to original sources
PubMed1992

TMJ biocompatible orthodontic treatment.

The papers summarized here indicate that TMJ dysfunction remains a complicated problem, requiring a multidisciplinary team approach. Psychological stress is an important factor in diagnosis. New concepts of joint function must be considered. The functional anatomy of the TMJ from an arthroscopic perspective should be studied. New treatment methods, such as the polycentric hinge joint articulator, should be considered. And finally, orthodontic diagnosis and treatment conventions need to be modified, from obtaining a complete history, clinical examination, arriving at a diagnosis and obtaining informed consent for treatment that may include psychological counseling, splint therapy, simultaneous fixed orthodontics and splint therapy and possible TMJ arthroscopic surgery for nearly all orthodontic patients.

Arthroscopy↗
PubMed1990

Can computed tomography of the chest stage lung cancer? Yes and no.

To determine the accuracy of computed tomography (CT) of the chest in the staging of lung cancer, we studied 418 patients with primary pulmonary carcinoma between 1979 and 1986. Each had a preoperative scan performed before detailed operative staging. Each CT scan was analyzed for components of the current TNM staging system. Computed tomography sensitivity and specificity for mediastinal lymph node metastasis were 84.4% and 84.1%, with corresponding positive and negative predictive accuracies of 68.7% and 92.9%, respectively. When TNM stages were derived from CT scans, only 190 of 418 (45.4%) completely agreed with operative staging. An additional 53 of 418 (12.7%) predicted the correct stage, although components of the TNM system were incorrect. In 94 of 418 scans (22.5%) CT overestimated the stage, whereas in 81 (19.4%) CT downgraded the stage. Computed tomography suggested metastatic lesions in liver, lung, adrenal gland, bone, or abdominal lymph nodes in 40 of 373 scans (10.7%); only five of 40 (12.5%) had documented metastasis. In summary, CT of the chest cannot accurately stage primary lung carcinoma according to the TNM classification. Because the negative predictive accuracy for mediastinal lymph node metastasis remains high (92.9%), invasive staging can be deferred for definitive thoracotomy when no lymphadenopathy is evident on CT. The high negative predictive accuracy for scans of the chest and upper abdomen makes CT a useful tool for exclusion of metastatic disease.

Adenocarcinoma↗
PubMed1990

Do deviations from radiance-invariance of metameric matches contradict the three pigment theory of foveal trichromacy?

According to the pigment theory of matching, metameric matches result from the equation of the rates of photoisomerizations for each of the three classes of cone pigments excited by the two matched fields. If true, matches are radiance-invariant and additive. Tests of the theory in this paper show small but ubiquitous failures in radiance-invariance due to systematic rather than random errors in matching. A choice between two possible explanations for these systematic errors favors the view that in subjects who deliberately or intuitively search for the middle of the matching range, the errors are due to an asymmetry in the Weber fraction for color (Trezona) at low (but not high) levels of retinal illuminance.

Analysis of Variance↗
PubMed1990

The change in the neutral point of dichromats with change in the angle of incidence of monochromatic light on the retina.

The hypothesis was tested that the change in the perceived color of monochromatic light with change in its angle of incidence on the retina can be accounted for completely by prereceptor factors alone. This was evaluated by measuring the change in the match of a monochromatic light to a fixed (and normally incident) white light as the monochromatic beam changed its traverse through the eye from chief ray to "off-axis" retina incidence at the margin of the exit pupil. Two protanopes and four deuteranopes were tested. In each case, the wavelength of the chief ray at the match was consistently, reliably, and (statistically) significantly larger than that of the match with the "off-axis" beam. The result cannot be accounted for by prereceptor factors alone.

Color Perception↗
PubMed1987

The change in color matches with retinal angle of incidence of the colorimeter beams.

Differences between W.D.W. chromaticities of monochromatic lights obtained with all colorimeter beams incident on the retina "off-axis" and those found for lights striking the retina normally have been studied throughout the visible spectrum on 4 normal trichromats. The results are inconsistent with: (i) the assumption in Weale's theories of the Stiles-Crawford hue shift that the sets of absorption spectra of the visual pigments catching normally and obliquely incident photons are identical, and (ii) "self-screening" explanations for the change in color with angle of incidence on the retina. The color matching functions of a protanomalous trichromat are inconsistent with the hypothesis that the absorption spectra of the visual pigments catching normally incident photons in his retina are those catching obliquely incident photons in the normal retina.

Color Perception↗
PubMed1987

"Self-screening" of rhodopsin in rod outer segments.

Microspectrophotometry (MSP) shows rhodopsin highly concentrated (about 3.0 mmol/l) in rod outer segments (ROS). Calculation of the in vivo absorption spectrum of human rhodopsin from such data reveals a striking failure to agree with the action spectrum of human rod vision. Agreement is good between the spectral distribution of absorption coefficients and the action spectrum, but the "concentration-broadening" (or "self-screening") introduced by the high end on absorbance at this concentration results in a misfit among the largest in the 93 years comparisons of this kind have been made! To deal with this anomaly, it has been suggested that "concentration-broadening" is inappropriate for rhodopsin in rod vision. This proposal was tested by comparing rod action spectra of 15-day-old and adult rats, since the lengths of ROS increase by a factor of about two in maturation. Three lines of evidence are inconsistent with it. Although the conundrum remains unexplained, it cannot be dismissed by supposing "self-screening" inappropriate for night vision.

Aging↗
PubMed1987

A note on the action spectrum of human rod vision.

A template representing the spectral distribution of the absorption coefficients of human rhodopsin was fitted to each of 59 individual action spectra of human rod vision (from one of three populations) by an optimization routine. Curve-fitting parameters included peak wavenumber, optical density at this wavenumber and (for those from the population neither aphakic nor constrained to ages where the standard lens transmissivity curve is supposed valid), density of the latter at the wavenumber of peak lens absorption. The average peak wavenumber of each population differed significantly from that of the other two. Either the standard curve of lens absorption (even with peak lens density as a curve-fitting parameter) is inappropriate for correcting the normal spectrum or the rhodopsins in the retinas of these populations do not all have identical wave-numbers of peak absorbance.

Adolescent↗
PubMed1986

The Stiles-Crawford effect of the second kind (SCII): a review.

The background which led Stiles to the discovery that the color of a monochromatic ray of light varied with its angle of incidence on the retina, and the developments in the subject since 1937 when this discovery was reported are summarized. Stiles's original measurements of the 'hue shift' did not successfully quantify SCII in every part of the spectrum, since it provided only two degrees of freedom while the color changes sometimes require three. Nevertheless, they were the paradigm for most subsequent work for the next quarter of a century. Full quantification of the effect was first obtained by trichromatic matching on Stiles's NPL trichromator almost 25 years after the initial discovery. The phenomena were then also fully described quantitatively with an elaboration of Stiles's original theory ('self-screening' theory), on the assumption that the ordinary laws of additivity are valid for color matches of three primaries striking the retina at one angle of obliquity to a test incident at a different angle. More recent experiments suggest that this initial assumption may not be generally true and that 'self-screening' theory may not generally provide a satisfactory description of the color changes throughout the visible spectrum, even for measurements of the effect obtained under conditions in which the additivity assumption seems to be valid. However, the available data strongly imply that absorptions of photons obliquely incident on foveal cones depend upon spectra clearly different from those upon which absorptions of normally incident photons depend.

Color Perception↗
PubMed1985

Electroretinograms evoked by sinusoidal excitation of human cones.

The amplitude and phase of the fundamental Fourier component of the human electroretinogram (e.r.g.) were recorded with a synchronous detection method under conditions in which each of the three species of cones can be assumed most sensitive in turn. Weber-Fechner behaviour is well established at, or more distal in the retina than, the source of these voltages. Results over the frequency range 7-50 Hz exclude a diffusion model of human flicker perception. The e.r.g. phase vs. frequency plot found with a 'red' test differs from that obtained with a 'green'. The shapes of the e.r.g. field sensitivity action spectra agree with those of the subject's IIj(mu) (j = 3, 4 and 5) mechanisms of Stiles and with in situ measurements of the absorbance spectra of human cone pigments. Threshold phase with each test was independent of background wave-length but, consistent with the results in 3, the phase of the response to the 'red' test (25 Hz) differed significantly from that to the 'green'. If these differences resulted from the absorption of test photons of different colours at different points along the outer segment (independent of cone spectral sensitivity), they would be as clear on dichromats as on trichromats. Results on a protanope are inconsistent with this prediction. We infer that differences in phase are due to the different kinetics of different cone mechanisms and that the e.r.g.s studied here are evoked by exciting only the most sensitive cone mechanism, even though dark-adaptation studies prove that at e.r.g. threshold the test is well above psychophysical threshold for all three cone species. If the inference in 5 is correct, studies of sensitivity across the retina suggest that the spatial distribution of long-, middle- and short-wave-sensitive cones in the human retina differ remarkably.

Dark Adaptation↗
PubMed1979

Lack of uniformity in colour matching.

1. The fraction of red in a red--green mixture matched to yellow increased as the intensities of the match constituents were increased sufficiently to bleach appreciable chlorolabe and erythrolabe. 2. All changes in matching found for a given normal trichromat, (i) with increase in the intensities of the matching components, (ii) as a function of time after the onset of very intense components, (iii) with change in the pupil region through which light enters the eye, and (iv) with change in the region of the retina under test, are consistent with the assumption that matching depends upon the absorption of light in three kinds of (individually colour blind) cones, each with its own visual pigment, provided that the lambda max densities of the latter can vary in the range 0.25--1.0 (common logarithmic units) depending upon the subject. 3. Individual differences in matching among normal (as well as among both varieties of red--green anomalous) trichromats, on the other hand, suggest that the extinction spectra of the cone pigments sensitive to long and medium wave lengths may differ from one trichromat to the next.

Adolescent↗
PubMed1977

Cone pigments in human deutan colour vision defects.

1. The Nagel anomaloscope, neutral points and dichromatic matches to a spectral green light identified a population of seventy red-green dichromats. 2. The anomaloscope settings allow the calculation of the relative action spectrum of the match at the wave-length of the red (645 nm) and green (535 nm) primaries. The distribution of this ratio is bimodal; there are two clusters with a gap of about 0-75 long units between. Among the thirty-eight deuteranopes there are wide differences in anomaloscope matches; similar differences appear among the thirty-two protanopes. 3. Retinal densitometry of the foveas of fifteen of the deuteranopes is compared and contrasted with measurements on trichromats. In the former, only one photolabile pigment is found in the red-green region of the spectrum; normals always have two. The view of Rushton (1965a) that deuteranopes have erythrolabe but no measurable chlorolabe is confirmed for each member of this group. 4. Simple deuteranomalous show two red-green cone pigments. The difference spectra of extreme deuteranomalous are very similar to those found in deuteranopia. 5. Individual differnce in kinetics (photosensitivity, time constant of regeneration) and in the density and lambdamax of the difference spectrum of erythrolabe in deuteranopia are appreciable; the reasons for these differences are not clear.

Color Vision Defects↗