Biomedical subjects

D H Krantz

Publications and source records attributed to D H Krantz.

10 recordsLinked to original sources

PubMed1995

The treatment of non-HIV-related conditions in newborns at risk for HIV: a survey of neonatologists.

OBJECTIVES: The purpose of this study was to examine attitudes of neonatologists about treatment of conditions unrelated to the human immunodeficiency virus (HIV) for critically ill newborns at risk for HIV. METHODS: Questionnaires were mailed to the 1508 members of the Section on Perinatal Medicine of the American Academy of Pediatrics; 63% completed the survey (n = 951). The survey included structured questions about treatment for hypothetical cases and open-ended questions eliciting reasons for decisions. RESULTS: Differences in recommendations for treatment by both maternal and infant HIV status were substantial and statistically reliable. For example, 98% of respondents recommended life-saving cardiac surgery for a neonate with no risk for HIV, but only 93% recommended such surgery for a child of an HIV-positive mother; only 50% recommended the same surgery for a newborn known to be infected. The corresponding figures for chronic dialysis were 91%, 61%, and 26%. Most expected diminished quality of life for both infected and uninfected children of HIV-positive mothers. CONCLUSIONS: Recommendations about life-sustaining treatment for non-HIV-related conditions varied by HIV status. These data on physician attitudes raise the possibility that infants labeled as HIV positive, whether infected or not, may suffer discrimination.

Adult↗

PubMed1983

Classical tritanopia.

1. A subject who has suffered from central serous chorio-retinopathy in his left eye noticed differences in the colour of a given light as perceived by each eye alone. Standard screening tests (colour order and colour matching) indicated a tritan defect in the left eye; the right eye was normal on these tests.2. The subject was dichromatic in his left eye, trichromatic in his right. The left-eye distimulus colour-matching functions, spectral luminosity, and wave-length discrimination functions were indistinguishable from corresponding data for congenital tritanopia. Comparable right-eye data were normal.3. Spectral dichromatic colour matches were invariant under changes of intensity and under addition of a common light to both halves of the field. (Grassmann's laws of linearity are satisfied.)4. Increment threshold versus intensity (t.v.i.) curves for a blue (481.9 nm) test on a yellow background yielded the normal three branches (for Pi(4)(mu), Pi(1)(mu) and Pi(3)(mu) respectively) in the trichromatic eye. In the dichromatic eye a single mechanism was found. It had the field sensitivity of Pi(4)(mu) whether measured with the blue, or with a violet (429.5 nm) test. No trace of Pi(3)(mu) or Pi(1)(mu) was ever discovered in the tritanopic eye. Both are normal in the trichromatic eye.5. The field sensitivities of Pi(4), Pi(5) and Pi(3) of the normal eye are well fitted by linear combinations of the spectral colour-matching functions of the trichromatic eye. Pi(4) and Pi(5) of the dichromatic eye are well fitted by linear combinations of the tritanopic matching functions.6. Colour matches made by the trichromatic eye do not match when viewed by the tritanopic eye, almost certainly because the ocular media of the two eyes have wave-length-dependent differences in absorption. For the largest difference (430 nm) the trichromatic eye transmits about 2.2 times more light than its fellow. When allowance is made for these differences, the field sensitivities of Pi(4) and Pi(5) of the two eyes do not differ. The field sensitivities of Pi(4) and Pi(5) of the normal eye, on the other hand, differ significantly from those of the average spectra obtained on four normal trichromats by Stiles, in a way that cannot be attributed to differences in transmittance of ocular media.7. It is concluded that classical (or acquired) tritanopia is not distinguishable in its manifestations from congenital tritanopia; furthermore, tritanopia can be regarded as a reduced form of normal trichromacy, once allowances are made for absorption of the ocular media and for variations among normal trichromats.8. Despite extensive search no evidence could be uncovered which might exclude the hypothesis that the colour vision in tritanopia depends exclusively upon absorption in only two foveal cone pigments, one long-wave-absorbing and one medium-wave-absorbing.

Adult↗

PubMed1983

Perception of colour in unilateral tritanopia.

The unilateral tritanope described in the previous paper (Alpern, Kitahara & Krantz, 1983) was able to match every narrow-band light presented to his tritanopic eye with lights from a tristimulus colorimeter viewed in the adjacent field by the normal eye. In two regions of the spectrum (called isochromes) physically identical lights appeared identical to the observer's two eyes. One isochrome was close to 'blue' for the normal eye, the other was in the long-wave spectral region seen by the normal eye predominantly as 'red'. Between these isochromes the normal eye required less than spectral purity to match, dropping to near zero purity at 560-570 nm. A mixture of the two isochromes that appeared purple to the normal eye appeared neutral to the tritanopic eye. Hence dichoptic matches grossly violate Grassmann's additivity law. For the normal eye colour naming conformed to typical normal results. For the tritanopic eye the results were coherent with those found by dichoptic matching: the spectrum was divided into two regions by the achromatic neutral band. To the short-wave side, only the colour names 'blue' and 'white' were ever used. To the long-wave side the predominant colour names were 'red' and 'white' with some 'yellow'. Spectral lights appeared neither 'red-blue' nor greenish. Surrounding the test with an annulus either 430 nm, 650 nm, or a mixture of these, fails to induce any greenish appearance, although the achromatic band shifted in the expected directions. It is concluded that there must be exactly three functionally independent, essentially non-linear central codes for colour perception, and that these codes are different from those suggested in existing theories of colour perception.

Adaptation, Physiological↗

PubMed1981

Visual pigment kinetics in abnormalities of the uvea-retinal epithelium interface in man.

In four patients with abnormalities of the interface between photoreceptors and their vascular supply, bleached visual pigments regenerated abnormally slowly, with double exponential time courses, although the time constant of the first exponential was abnormally fast. During therapy in one patient the slower exponential returned to normal early after treatment, whereas the fast component persisted even after clinically complete recovery. The results could be explained by the following hypothesis. In normal eyes, two pigment-regeneration routes exist, the more rapid (which depends on a short-lived intermediate) playing no role after a long full bleach. Uvea abnormalities cause slower regeneration in the normal main route and slower breakdown of the normally short-lived intermediate.

Adolescent↗

PubMed1980

The Poggendorff illusion: consider all the angles.

In the Poggendorff display, which consists of parallel lines interrupting a transversal, one of the two transversal segments was replaced by a dot lying along the parallel. The angle between the remaining transversal segment and the parallels was varied in 15 degree increments, as was the orientation of the transversal with respect to the subject. Subjects set the dot to appear collinear with the transversal. Judgmental errors can be partitioned into additive components, one linearly related to the size of the obtuse angle between transversal and parallels and the other a sinusoidal function of transversal and parallels and the other a sinusoidal function of transversal orientation (collinearity settings err toward the horizontal or vertical, whichever is closer), plus a meridional effect, an interaction term that magnifies the errors of a given obtuse angle as the transversal approaches an oblique orientation.

Discrimination Learning↗

PubMed1975