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Biomedical subjects

S Wittenberg

Publications and source records attributed to S Wittenberg.

At least 19 recordsLinked to original sources
PubMed2006

Insulin-like growth factor type-1 receptor down-regulation associated with dwarfism in Holstein calves.

Perturbations in endocrine functions can impact normal growth. Endocrine traits were studied in three dwarf calves exhibiting retarded but proportionate growth and four phenotypically normal half-siblings, sired by the same bull, and four unrelated control calves. Plasma 3,5,3'-triiodothyronine and thyroxine concentrations in dwarfs and half-siblings were in the physiological range and responded normally to injected thyroid-releasing hormone. Plasma glucagon concentrations were different (dwarfs, controls>half-siblings; P<0.05). Plasma growth hormone (GH), insulin-like growth factor-1 (IGF-1) and insulin concentrations in the three groups during an 8-h period were similar, but integrated GH concentrations (areas under concentration curves) were different (dwarfs>controls, P<0.02; half-siblings>controls, P=0.08). Responses of GH to xylazine and to a GH-releasing-factor analogue were similar in dwarfs and half-siblings. Relative gene expression of IGF-1, IGF-2, GH receptor (GHR), insulin receptor, IGF-1 type-1 and -2 receptors (IGF-1R, IGF-2R), and IGF binding proteins were measured in liver and anconeus muscle. GHR mRNA levels were different in liver (dwarfs<controls, P<0.002; dwarfs<half-siblings, P=0.06; half-siblings<controls, P=0.08) but not in muscle. IGF-1R mRNA abundance in liver in half-siblings and controls was 2.4- and 2.5-fold higher (P=0.003 and P=0.001, respectively) and in muscle tissue was 2.3- and 1.8-fold higher (P=0.01 and P=0.08, respectively) than in dwarfs. Hepatic IGF-1R protein levels (Western blots) in muscle were 2.5-fold higher (P<0.05) and in liver and muscle (quantitative immunohistochemistry) were higher (P<0.02 and P<0.07, respectively) in half-siblings than in dwarfs. The reduced presence of IGF-1R may have been the underlying cause of dwarfism in studied calves.

Animals↗
PubMed1993

Pinhole eyewear systems: a special report.

Multiple pinhole discs are being promoted as part of systems claimed capable of correcting refractive error. Attempts to mitigate refractive error utilize training attributable to the systems of Bates, Peppard, and Huxley. The pinhole discs provide an array of 0.9mm apertures separated by 3mm horizontally and vertically. Because of the small aperture size, some of the optical advantages of the pinhole are offset by diffraction effects. The discs can produce multiple images and the visual experience of individuals will be a function of the user's pupil size and refractive error. These are discussed both theoretically and based on the author's observations wearing the spectacles.

Equipment Design↗
PubMed1989

Clinical comparison of the TruVision Omni and four progressive addition lenses.

The TruVision Omni is a progressive addition lens (PAL) using a bipolar design and the Dirichlet principle to minimize optical aberrations. The design was evaluated by having each patient elect to keep one lens type after masked paired comparison of the TruVision Omni with one of four other PAL types: VIP, Varilux, New Super NoLine, and Gradal HS. The Omni was chosen most frequently in each case: 16 to 8, 17 to 6, 18 to 6, and 15 to 3, respectively. Thirty-seven percent reported that no adaptation was required with the Omni compared to 20% for the paired PAL. In terms of specific performances, Omni tended to rank highest for intermediate distance functions and freedom from distortion, average for distance functions, and slightly above average for near function. The data support the merit of Omni's design strategy.

Adult↗
PubMed1988

The Badal optometer paradox.

Badal's optometer is used to change the vergence of the accommodative stimulus without changing retinal image size. It has been accepted that this can be accomplished by putting the optometer's secondary focal point at either the eye's anterior nodal or anterior focal point. I show that there can be only one solution because the simultaneous truth of both solutions would lead to a paradox. The most precise solution is slightly different for the accommodated and the unaccommodated eye, but the nodal point provides the best general solution. For the accommodating eye there is a residual increase in image size with accommodation due to the anterior displacement of the nodal points. For the unaccommodated eye, the correct reference point is its entrance pupil. Use of the nodal point results in accommodation creating an anomalous, but slight, change in retinal image size.

Accommodation, Ocular↗
PubMed1986

Solar radiation and the eye: a review of knowledge relevant to eye care.

Solar radiation has been implicated, with a variety of evidence, as a causative agent in photokeratoconjunctivitis, pinguecula and pterygium, nodular band keratopathies, epidermoid carcinoma, cataract, solar retinopathy, and macular degeneration. Much of the support for claims relating to chronic conditions having serious consequences and significant prevalence in the United States rests on investigations using animals and short-time exposures at high intensities. The direct applicability of these studies to humans in natural environments is uncertain, but they have been relied on because one cannot deliberately induce significant trauma in humans. The use of animal data is made difficult by the need to convert animal thresholds to human equivalents, to equate laboratory cycles and magnitudes of exposure to those in the natural environment, and to quantify the impact of avoidance and protective mechanisms. Risk can be assessed adequately only by epidemiological studies, but their potential has been only partially realized because of poorly controlled confounding variables. Epidemiologic evidence suggests that corneal trauma from ultraviolet radiation (UVR) is a risk of prolonged exposure in regions containing much ultraviolet (UV) or in highly reflective environments. The impact of UV-B on cataractogenesis has been investigated inadequately and no evidence exists for retinal trauma arising from routine exposure in even the brightest surroundings. However, there can be no question that enough solar energy reaches the earth to harm the eye if unattenuated. Damage to vision as a result of direct solar viewing demonstrates that unequivocally. The lack of clear evidence of radiation damage occurring other than in regions of high reflectivity and/or low horizons suggests that in normal surroundings there is little or no risk to the eye, although more careful epidemiological investigation is required before all concern can be ruled out completely. The major improvement required is the quantification of individual exposure histories. This step is necessary if we are to make significant progress toward better understanding the practical impact of solar radiation on the eye.

Conjunctiva↗
PubMed1981

Brock's research in stereopsis.

While Frederick Brock's contributions to vision training are numerous, little of his work dealt specifically with stereopsis, mostly concentrating on its application to diagnosis and therapy of binocular dysfunction. He did demonstrate, qualitatively, how differences in the size or clarity of retinal images affect stereopsis. The theoretical basis of his work, as well as his published and unpublished contributions, are reviewed in the context of the author's personal experience with this singular person.

Depth Perception↗
PubMed1978

Evaluation of the pneuma-tonometer.

Intraocular pressure in 125 randomly selected patients visiting the eye clinic at the Massachusetts Institute of Technology for routine care was measured with a Goldmann applanation tonometer and a model 30R Pneuma-Tonometer. Pairs of reading were taken with each instrument when possible, and each trace of the Pneuma-Tonometer measurement was subsequently read blind and independently by two observers. The standard deviation of the differences between the two readers' values obtained on 416 traces was 0.44 mm Hg. The standard deviation of the differences between paired Pneuma-Tonometer readings on 186 eyes was 1.75 mm Hg. With data selected for cause the mean Pneuma-Tonometer reading was 0.40 mm Hg higher, the standard deviation of the differences between the instruments was 1.50 mm Hg, and the correlation coefficient was 0.88. Alternatives to the customary use of linear regression methods of assessing calibration are proposed.

Calibration↗
PubMed1977

A clinical evaluation of the non-contact tonometer.

Paired non-contact tonometer readings were taken on patients at the Boston City Hospital Eye Clinic before and after routine vision care that included Goldmann tonometry. The variability of NCT readings was determined and comparisons made between readings obtained with the NCT and Goldmann instruments. The regression equation relating the pre-Goldmann NCT findings (N1), to the Goldmann (G), was N1 = 1.01G + 1.97; and the equation relating the post-Goldmann NCT findings (N2), to the Goldman was N2 = .94G + 1.70. The N1 mean was 2.06 mm. higher than the mean G, while the N2 mean was .58 mm. higher than the mean G. The correlation coefficients and standard deviation of the differences for the two comparisons were, .88, 3.91, and .93, 3.07, respectively. The Goldmann findings therefore were seen to agree more closely with the NCT findings taken after them. The linear regression and correlation coefficients between the NCT and the Goldmann were generally in good agreement with those of prior studies, although the standard deviations of the differences between findings were larger in this study. This result is not surprising since no attempt was made to train Goldmann operators to criterion or to limit variability induced by differing observer criteria or by the use of only one Goldmann operator. The operators of the Goldmann tonometer had varying degrees of training as residents in ophthalmology. Interestingly, the agreement between pre-Goldmann NCT and post-Goldmann NCT findings was not good. This suggested that the taking of the Goldmann findings themselves may have had a significant effect on the tonometric readings and that the considerable time that frequently took place between the two sets of NCT readings could have affected the value. The standard deviation of the differences between pre- and post-Goldmann readings on the same patient was 3.27 as compared to that for paired readings which was 2.28. The data also showed a much better agreement between the NCT and the rechecked Goldmann findings than between the initial Goldmann findings and the rechecked Goldmann findings, indicating that where discrepancies existed, it was more likely that they were due to the Goldmann instrument.

Boston↗