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Biomedical subjects

J S Werner

Publications and source records attributed to J S Werner.

At least 19 recordsLinked to original sources
PubMed1995

Individual differences in contrast sensitivity functions: longitudinal study of 4-, 6- and 8-month-old human infants.

Contrast sensitivity functions (CSFs) of 25 infants were measured longitudinally at 4, 6 and 8 months of age using a preferential-looking method and the method of constant stimuli. Sine-wave gratings varied from 0.27 to 4.32 c/deg, contained eight unattenuated cycles (with edges tapered to uniform gray), and rose to the desired contrast in 2 sec. (1) The average CSF was described on log-log coordinates by a band-pass function. With development it increased in overall sensitivity to contrast, shifted its peak toward slightly higher spatial frequencies, and increased its high frequency cutoff. (2) Log sensitivity at the CSF peak was slightly higher for female than male infants at 6 months, consistent with the hypothesis that vernier acuity (which also may differ between the sexes at this age) is partly mediated by analyzers tuned to low frequencies. (3) Within age groups the individual differences were such that log sensitivities for neighboring spatial frequencies generally correlated more highly than distant frequencies. With development the correlations among distant frequencies below 1.0 c/deg increased. Monte Carlo simulations of a model that shifts spatial analyzers to higher frequencies with age reproduced these results but simulations of adultlike, unshifting analyzers did not. (4) Measures taken 2 months apart tended to correlate more highly than those taken 4 months apart, though some individual differences in the CSF peak remained stable over 4 months.

Aging↗
PubMed1995

Spectral efficiency measured by heterochromatic flicker photometry is similar in human infants and adults.

Spectral efficiency functions based on heterochromatic flicker photometry (HFP) were measured for three adults and 42 infants using a rapid visually-evoked potential (VEP) method. A 5 degrees-diameter, broadband standard (0.6 cd/m2) was presented in square-wave counterphase (15 Hz) with one of 13 monochromatic lights (420-660 nm; 20 nm steps). The intensity of the monochromatic light was continuously varied while extracting the phase-locked VEP amplitude of the fundamental component. HFP functions measured psychophysically by the method of adjustment were also obtained for the adults. Adult HFP functions from the two methods were found to be essentially the same. Both of these functions were compared to Vos'-modified 2 degrees V(lambda) function and the 10 degrees CIEV(lambda) function. The mean adult data were slightly better fit to the 2 degrees V(lambda) function than to the 10 degrees CIEV(lambda) function, although there was an elevation in sensitivity at 420 and 440 nm. Infant HFP functions were similar to Vos' modified V(lambda) except for an elevation in efficiency at short wavelengths. The mean infant HFP function agreed better with the 10 degrees CIEV(lambda) function than Vos'-modified V(lambda) function, but infant sensitivity was elevated by 0.4 log units at 420 nm compared to the 10 degrees CIE observer. The elevation found at short wavelengths for both adults and infants is attributed to individual and age-related variation in the density of the ocular media, and to reduced macular pigment screening resulting from use of a 5 degrees field size.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Contributions of neural pathways to age-related losses in chromatic discrimination.

Chromatic-discrimination thresholds were measured for light mixtures lying along individually determined tritan axes and an axis of constant short-wavelength-sensitive- (S-) cone stimulation for 30 color-normal observers (age range 22-77 years). The stimulus was a foveally viewed 2 degrees, circular bipartite field consisting of a standard and a test light. Heterochromatic flicker photometry was used to equate the retinal illuminance of the stimuli at 120 Td for all observers. All stimuli were presented in Maxwellian view. Age-related losses in chromatic discrimination depended on the level of cone stimulation. At relatively lower levels of S- and long-wavelength-sensitive (L-) cone stimulation, discrimination thresholds were elevated for older relative to younger observers. As the level of simulation increased for these two cone types, thresholds converged, on average, for all observers. Application of a model of chromatic discrimination mediated by an S-cone pathway suggests that there is no significant age-related change in Weber fractions and that age-related losses in chromatic discrimination are due, at least in part, to spontaneous neural noise arising in the pathway and/or neural changes that multiplicatively scale all incident light.

Adult↗
PubMed1994

Effect of cataract surgery on contrast sensitivity and glare in patients with 20/50 or better Snellen acuity.

The effect of cataract surgery was assessed in 103 patients whose visual acuity, as measured in dim light and with high contrast Snellen letters, was 20/50 or better. The patients desired cataract surgery. They complained of glare symptoms, had given up driving at night, or both. Contrast sensitivity was measured under simulated night conditions with a calibrated Vistech MCT 8000 device. No patient who had a contrast sensitivity of less than 27 at 6 cycles per degree (20/70 "equivalent acuity") had cataract surgery. The mean preoperative contrast sensitivity function showed abnormally low values for all frequencies (cycles/degree) tested. Postoperatively the values returned to normal. Of 99 patients who answered a postoperative questionnaire, 41 (41%) had been driving at night preoperatively and 80 (80%) were driving at night postoperatively. A control group of 24 noncataractous patients (48 eyes) was in the normal range of the test device used. These results support the view that the benefits of cataract surgery are not well predicted by Snellen acuity, even though functional vision may be significantly reduced.

Aged↗
PubMed1992

Sites of age-related sensitivity loss in a short-wave cone pathway.

The age-related losses in the sensitivity of a short-wave (S) cone mechanism were determined by measuring the threshold-versus-radiance (t.v.r.) functions for nine older (mean age, 71.0 years) and six younger (mean age, 24.4 years) subjects. Measurements were obtained for a 250-ms, 1.03 degrees-diameter, 440-nm foveally viewed test light presented on 470-nm adapting fields and on a 570-nm auxiliary field. A comparison of t.v.r. functions revealed intensity-dependent sensitivity losses in the older group. By applying a quantitative model of an S-cone pathway to the t.v.r. data obtained from the older subjects, we found that the age-related changes in the ocular media and the receptor sensitivities can account for much but not all of the difference in the sensitivity of an S-cone mechanism demonstrated by eight of our nine older subjects.

Adolescent↗
PubMed1991

The invariance of unique white; a possible implication for normalizing cone action spectra.

The locus of unique white was measured for two observers over a wide range of stimulus intensities, using both direct matching and absolute judgements. Chromaticity coordinates of each observer's unique white were found to be invariant over a range of about 4 log units. This result is discussed in the context of the class of models that explain the intensity-evoked change in perceived color (Bezold-Brücke effect) on the basis of response compression in color channels. Invariance of unique white may be interpreted, then, as evidence for its non-polarizing effect on color channels, including the three classes of cones. On the basis of that assumption we have used unique white as criterion for normalizing cone action spectra. Assuming an equal-energy spectrum for the standard observer's unique-white stimulus, as we found to be consistent with literature data, we calculated the associated coefficients of the conversion formulae between CIE space and cone space (both for XYZ to LMS and LMS to XYZ) of the Vos-Walraven (1971 Vision Research, 11, 799-818) and Smith-Pokorny (1975 Vision Research, 15, 161-171) receptor fundamentals. The action spectra that thus result, intersect at the spectral neutral (achromatic) points of the three classes of dichromats.

Color Perception↗
PubMed1991

Children's sunglasses: caveat emptor.

Spectrophotometric measurements were obtained on 40 pairs of children's sunglasses. Some of these sunglasses provide excellent protection from the potentially damaging effects of ultraviolet radiation (UVR), whereas others fail to provide adequate protection for the crystalline lens and retina. Some labels were ambiguous and misleading with respect to whether the sunglass provided adequate absorption of UVR.

Child↗
PubMed1990

Light, vision, and aging.

Recent research on aging of chromatic and spatial vision processes is reviewed. Changes in these visual processes with advancing age are largely continuous. Age-related declines in visual performance may be explained in terms of reductions in the illuminance of the visual stimulus due to changes in the ocular media and losses of efficiency at a neural level. Thus, some prominent characteristics of the senescent visual system are similar to those of the younger visual system operating at a lower ambient light level. One important determinant of retinal aging may be the light history of the individual, i.e., cumulative exposure to high-energy photons from solar radiation may accelerate retinal aging. If these abstractions from the literature are valid, then it will become more important to control the light environment throughout the life span.

Aged↗
PubMed1990

Additivity of spatially induced blackness.

Tests of additivity of the postreceptoral pathways that mediate the perception of blackness were conducted under conditions of spatial contrast. Observers increased the radiance of a surrounding annulus until a broadband (white) test center appeared completely black. Additivity tests with heterochromatic flicker photometry (HFP) and direct brightness matching were also conducted for each observer. The results indicated that the luminance level of the annulus required to induce blackness did not change with variations in spectral composition. Results consistent with additivity were also obtained for HFP, but the results from brightness matching were not consistent with additivity. The data support the view that the perception of blackness is mediated by neural mechanisms that additively combine the input of middle- and long-wave photoreceptors.

Adult↗
PubMed1990

Loci of spectral unique hues throughout the life span.

Spectral unique hues (blue, green, and yellow) were determined for 50 observers ranging in age from 13 to 74 years. Each unique hue was measured at three luminance levels (0.5-log-unit steps). There were no significant changes in the spectral locations of red-green equilibrium hues (unique blue and yellow) as a function of luminance level or age. In contrast, significant shifts in unique green loci occurred as a function of both age and luminance. Unique green loci shifted toward shorter wavelengths with age. These results are consistent with the hypothesis that with advancing age there is a parallel decline in the input of all three cone types to the red-green chromatic channel and either a selective decline in short-wave-sensitive cone input to the yellow-blue chromatic channel or a change in the way in which cone signals are combined within the yellow-blue channel.

Adolescent↗
PubMed1990

Sexual assault evidence collection.

The evidentiary exam following sexual assault provides crucial evidence that can be used by the prosecuting attorney to obtain a conviction in sexual assault cases. Evidence is collected for three purposes: to corroborate the use of force; to corroborate that recent sexual contact occurred; and to identify the perpetrator. Relatively few assailants (4%) go to jail for rape. To a great extent this is because of a lack of corroborating evidence and misinterpretation of this lack of evidence by police, courts, and jurors. This paper presents the results of a study to determine the likelihood of obtaining corroborating evidence of recent coitus along with an explanation of what negative results mean. Based on the results, recommendations are presented for sexual assault evidence collection in emergency departments.

Acid Phosphatase↗
PubMed1989

UV-absorbing intraocular lenses: safety, efficacy, and consequences for the cataract patient.

The crystalline lens absorbs most of the incident UV radiation between 300 and 400 nm and thereby protects the retina from a significant, potential source of photochemical damage. This protection is lost when the lens is removed by cataract surgery, but can be restored by the implantation of an intraocular lens (IOL) that has UV-absorbing chromophores incorporated into a polymethylmethacrylate (PMMA) substrate. Spectrophotometric data show that the various, commercially available, UV-absorbing IOLs are not equally effective in absorbing UV radiation; thus, a standard, quantitative metric for comparing their performance is proposed. Cytotoxicity and biocompatibility studies have failed to demonstrate that UV-absorbing IOLs are unsafe, even when damaged by Nd:YAG lasers used for photodiscission posterior capsulotomy. There are positive consequences for the pseudophakic patient with a UV-absorbing IOL, in that it may restore normal spectral sensitivity, reduce erythropsia and cystoid macular edema, and stabilize the blood-vitreous barrier.

Cataract Extraction↗
PubMed1989

Temporal induction of blackness--I. Color appearance.

Three color-normal observers described the appearance of colors under conditions of temporal induction. One of four inducing fields (unique blue, unique green, unique yellow, unique white) was foveally viewed for 5 sec followed immediately by a 400 msec reference stimulus of the same size (0.75 deg) and spatial location as the inducing field. The reference stimulus was 3 or 5 td and appeared achromatic to the observer when viewed without the inducing field. After presentation of this temporal sequence, the observers described the reference stimulus by assigning percentages to the terms red, green, yellow, blue, white and black. The range of inducing field intensities was -0.4-3.2 log td. Both chromatic and achromatic induction occurred at low illuminance levels of the inducing fields. As the illuminance of the inducing field increased, the reference stimulus gradually became blacker and the chromatic components less prominent. The minimum illuminance level at which the reference appeared 100% black was the same for the four different inducing fields.

Adult↗
PubMed1989

Temporal induction of blackness--II. Spectral efficiency and tests of additivity.

The perception of blackness was investigated by measuring spectral efficiency and field additivity under conditions of temporal induction. For both purposes, observers foveally viewed a 0.75 deg, inducing stimulus for 5 sec followed immediately (or 200 msec later) by a broadband (5500 K) reference stimulus of the same size and spatial location. For spectral efficiency measurements, the inducing field was a monochromatic light between 400 and 700 nm (10 nm steps), while the additivity studies involved various wavelength mixtures. The psychophysical task was to increase the radiance of the inducing field until the reference stimulus just turned completely black. For two observers the spectral efficiency function of temporally-induced blackness more closely resembled their heterochromatic flicker photometry (HFP) function than their direct brightness-matching function. Their brightness functions were characterized by an inflection at about 580 nm which is generally ascribed to subtractive cone interactions, but their blackness-induction and HFP functions did not show this inflection. The brightness function of the third observer did not show an inflection at 580 nm, thereby making it difficult to differentiate between her three spectral efficiency functions. Overall, the subtle differences between the various spectral efficiency functions made it difficult to determine whether blackness induction was more similar to HFP or brightness matching. The results from the additivity tests of blackness induction, HFP and direct brightness matching removed this ambiguity from the spectral efficiency findings. Blackness induction and HFP were shown to be additive, whereas the results from brightness matching showed clear additivity failures of the cancellation type. These data support the view that the perception of blackness is mediated by neural mechanisms that additively combine the inputs of middle- and long-wave photoreceptors.

Adult↗
PubMed1989

Loss of human photoreceptor sensitivity associated with chronic exposure to ultraviolet radiation.

The crystalline lens of the human eye absorbs most of the incident ultraviolet radiation (UVR), but when the lens is removed, this radiation can reach the photoreceptors. The consequences of UVR exposure on cone receptor sensitivity were determined from psychophysical measurements in patients who had undergone bilateral cataract extraction and implantation of intraocular lenses (IOLs). The IOL implanted in one eye contained chromophores that absorb incident UVR, whereas that implanted in the other eye transmitted UVR. Five years of exposure to ambient UVR was associated with a selective loss in sensitivity of the short-wave cone photoreceptors. These results are consistent with the hypothesis that chronic exposure to UVR may damage the human retina.

Aged↗