Biomedical subjects

J S Werner

Publications and source records attributed to J S Werner.

At least 19 recordsLinked to original sources

PubMed2005

Night vision in the elderly: consequences for seeing through a "blue filtering" intraocular lens.

Relative scotopic spectral sensitivity depends only on the rhodopsin photopigment and ocular media absorption spectra. Rhodopsin is well characterised so the relative scotopic spectral sensitivity function can be calculated for intraocular lenses (IOLs) of known spectral density. In a recent perspective, Mainster and Sparrow concluded that an IOL with short wave absorbing chromophores would provide more retinal protection than conventional IOLs, but the practical consequences for scotopic vision are unclear. This paper uses published experiments to examine the implications for scotopic vision of the IOLs analysed by Mainster and Sparrow. A 14.6% reduction in scotopic sensitivity is expected for a SN60AT (AcrySof Natural) compared to a SA60AT (Conventional AcrySof) IOL under broadband illumination (equal quantum spectrum). This effect (0.07 log unit) is visually insignificant in relation to the approximately 4.0 log unit range of scotopic sensitivity. More importantly, it is expected that scotopic contrast sensitivity would be reduced by only approximately 0.01 log unit. It is thus improbable that a difference in scotopic vision between observers with the Natural and Conventional IOLs could be reliably detected using broadband stimuli.

Absorption↗

PubMed2001

Filling-in of the foveal blue scotoma.

The blue-blindness (tritanopia) of the human foveola normally goes unnoticed but can be directly visualized by having observers view a flickering, monochromatic, short-wavelength field. The blue scotoma appears as a tiny dark spot in central vision, the visibility of which depends upon the wavelength of the field and the temporal frequency of modulation. Comparisons of fading times as a function of flicker frequency for the blue scotoma, foveal afterimages and optically stabilized images indicate a common time course, consistent with the hypothesis that perceptual filling-in of the foveal blue scotoma reflects the operation of neural processes similar to those involved in fading and regeneration of stabilized images.

Afterimage↗

PubMed2001

Nurses' attitudes toward pain, pain assessment, and pain management practices in long-term care facilities.

This descriptive study was designed to identify attitudes regarding pain as well as pain assessment and management practices of nurses working with elderly residents in 10 long-term care facilities. Twenty-seven nurses from 10 facilities in the Midwest responded to a questionnaire. Findings indicate that more than half of the respondents reported that residents should be pain free; however, only 5 respondents defined pain free as no pain. Others defined it as being comfortable or able to perform activities of daily living. Nurses reported assessing the following aspects of pain more than three fourths of the time: onset, frequency, location, severity/intensity, facial expression, contortions, and medication effectiveness. Changes in weight, recreational activity, and concentration, as well as coping skills were assessed less than half of the time. When first learning residents were in pain, nurses reported doing further assessments, offering medication, giving emotional reassurance, and changing the resident's position. They reported substantial familiarity with basic nonpharmacologic practices but only asked residents to try these interventions (in addition to medication) an average of 38% of the time.

Adult↗

PubMed2001

Age-related changes in wavelength discrimination.

Wavelength discrimination functions (420 to 620-650 nm) were measured for four younger (mean 30.9 years) and four older (mean 72.5 years) observers. Stimuli consisted of individually determined isoluminant monochromatic lights (10 Td) presented in each half of a 2 degrees circular bipartite field with use of a Maxwellian-view optical system. A spatial two-alternative forced-choice method was used in combination with a staircase procedure to determine discrimination thresholds across the spectrum. Small but consistent elevations in discrimination thresholds were found for older compared with younger observers. Because the retinal illuminance of the stimuli was equated across all observers, these age-related losses in discrimination are attributable to neural changes. Analyses of these data reveal a significant change in Weber fraction across adulthood for a chromatically opponent pathway receiving primarily antagonistic signals from middle-wavelength-sensitive and long-wavelength-sensitive cones but not for a short-wavelength-sensitive cone pathway.

Adult↗

PubMed2000

Time course of early mesopic adaptation to luminance decrements and recovery of spatial resolution.

The time course of recovery of spatial resolution following adaptation to a uniform field was measured for test probes presented at lower illuminance than the adapting field. Six observers were tested in a Maxwellian-view system using 20 degrees adapting fields of 1.6-2.6 log photopic trolands. Test stimuli were 7 degrees, 250 ms Gabor patches (1 and 6 cpd) of mean retinal illuminance 2-3 log units lower than the adapting field. During the 9 s after adapting field offset, contrast thresholds for orientation discrimination followed an exponential-decay function and showed longer recovery times for larger illuminance decrements and higher spatial frequency.

Adult↗

PubMed2000

Spatial summation in human cone mechanisms from 0 degrees to 20 degrees in the superior retina.

The maximum area of complete spatial summation (i.e., Ricco's area) for human short-wavelength-sensitive-(S-) and long-wavelength-sensitive- (L-) cone mechanisms was measured psychophysically at the fovea and at 1.5 degrees , 4 degrees , 8 degrees , and 20 degrees along the vertical meridian in the superior retina. Increment thresholds were measured for three observers by a temporal two-alternative forced-choice procedure. Test stimuli ranging from -0.36 to 4.61 log area (min2) were presented on concentric 12.3 degrees adapting and auxiliary fields, which isolated either an S- or an L-cone mechanism on the plateau of its respective threshold versus intensity function. Test flash durations were 50 and 10 ms for the S- and L-cone mechanisms, respectively. The data indicate that, from 0 degrees to 20 degrees, Ricco's area increases monotonically for the L-cone mechanism, is variable for the S-cone mechanism, and is larger for the S-cone mechanism than for the L-cone mechanism for essentially all retinal locations. This pattern of results most likely reflects differences in ganglion cell density and changes in neural convergence with retinal eccentricity.

Adult↗

PubMed2000

Senescence of foveal and parafoveal cone sensitivities and their relations to macular pigment density.

Foveal and parafoveal increment thresholds were measured for 50 observers (12-88 years of age) under conditions that isolated retinal mechanisms dominated by short- (S-), middle- (M-), or long- (L-) wave-sensitive cones. Thresholds were obtained on the plateau of the threshold-versus-intensity function of each isolated mechanism and were referred to the retina by using individual measurements of ocular media and macular pigment density. Age-related increases in foveal thresholds, specified at the retina, were found for all three cone mechanisms. Parallel sensitivity losses for each cone mechanism were also observed at 4 degrees and 8 degrees in the temporal retina. A significant positive correlation was found between foveal macular pigment density and the S-cone, but not the M- and L-cone, log sensitivity difference (0 degrees-8 degrees) specified at the retina. This relation is expected from the hypothesis that the macular pigment protects the photoreceptors from senescent losses in sensitivity. However, because this result is independent of age, it is interpreted as being due to local gain changes resulting from differential filtering of incident light by the macular pigment between the fovea and the parafovea.

Adolescent↗

PubMed1999

S-cone signals to temporal OFF-channels: asymmetrical connections to postreceptoral chromatic mechanisms.

Psychophysical tests of S-cone contributions to temporal ON- and OFF-channels were conducted. Detection thresholds for S-cone modulation were measured with two kinds of test stimuli presented on a CRT: a rapid-on sawtooth test and a rapid-off sawtooth test, assumed to be detected differentially by temporal ON- and OFF-channels, respectively. S-cone related ON- and OFF-temporal responses were separated by adapting for 5 min to 1 Hz monochromatic (420, 440, 450, 540, or 650 nm in separate sessions) sawtooth flicker presented in Maxwellian view. Circular test stimuli, with a sawtooth temporal profile and a Gaussian spatial taper, were presented for 1 s in one of four quadrants 1.0 degree from a central fixation point. A four-alternative forced-choice method combined with a double-staircase procedure was used to determine ON- and OFF-thresholds in the same session. Following adaptation, the threshold elevation was greater if the polarity of the test stimulus was the same as the polarity of the sawtooth adaptation flicker, consistent with separate ON- and OFF-responses from S-cones. This asymmetrical pattern was obtained, however, only when the adaptation stimuli appeared blue with a little redness. When the adaptation flicker had a clear reddish hue component, the threshold elevation did not depend on the polarity of the sawtooth test stimuli. These results are consistent with a model in which OFF-signals originating from S cones are maintained by a postreceptoral mechanism signaling redness, but not by a postreceptoral chromatic mechanism signaling blueness.

Adaptation, Ocular↗

PubMed1999

Senescent changes in scotopic contrast sensitivity.

Scotopic contrast sensitivity functions (CSFs) were measured for 50 observers between the ages of 20 and 88 years. Using a maximum-likelihood, 2-alternative, temporal forced-choice threshold-estimation algorithm, scotopic CSFs were measured at 7 spatial frequencies ranging from 0.2 to 3.0 cpd, with mean retinal illuminance equated for observers at -0.85 log scotopic Trolands. For each stimulus condition, eight cycles of a horizontal sinusoidal grating were presented within +/- 1 S.D. of a 2-D Gaussian-spatial envelope and within a 1-s Gaussian-temporal envelope. Stimuli were centered on the nasal retina along the horizontal meridian 6 degrees from the fovea. Scotopic CSFs were found to be low-pass. Statistically significant age-related declines in contrast sensitivities were found for spatial frequencies at or below 1.2 cpd. There was also a statistically significant decrease in the high frequency cut-off with age (P < 0.01). An explanation of these results in terms of optical factors is rejected, while the results are consistent with age-related changes in the magnocellular pathway.

Adult↗

PubMed1999

Forever young: visual functions not affected or minimally affected by aging: a review.

Six visual functions, once developed to adult levels of performance, have been noted to exhibit little or no alteration with aging (also see Appendix, Note 1). Those selected for more substantial discussions in this article are: (a) the Stiles-Crawford effect of the first kind (SCE-I), also known as the "directional sensitivity of the retina"; (b) specific vernier acuity paradigms (including alignment of two lines one with the other, and two- and three-point vernier alignment tasks); and (c) color vision-related perceptual constancies. Each of these functions has rather different origins in the visual system. The SCE incorporates optical waveguide photoreceptor properties and has both physical and physiological origins; vernier acuity (one of the hyperacuities) is largely the result of neural data processing mechanisms; and the color vision-related effects have their origins in retinal neural processes. Descriptions of additional visual functions minimally affected by age are presented as well. This recent research raises many questions. How can these visual responses be so stable, when so many other visual responses show decrements with aging? What does it mean if anomalous responses within the more stable functions are encountered in individuals? Can these age-resistant functions be employed to help sustain other functions in aging individuals? Are such relatively invariant functions limited to the visual system? Because of the stability of the reported responses with aging, these same relationships can be used as test controls for other studies of aging, and as benchmarks to distinguish between "normal" aging and disease processes.

Aged↗

PubMed1999

Aging and the saturation of colors. 1. Colorimetric purity discrimination.

Colorimetric purity (Pc) discrimination functions were measured for 21 color-normal observers (11 younger and 10 older observers with mean ages of 30 and 74 years, respectively). On each two-alternative-forced-choice trial, observers saw two flashes of light, a broadband white light [CIE(x, y) = (0.33, 0.35)] and a mixture of broadband and monochromatic light (420-680 nm). The observer's task was to choose the flash that had a chromatic component. Foveally viewed, circular, 1.2 degrees-diameter stimuli were presented as 1.5-s flashes with 3-s interstimulus intervals in Maxwellian view. Stimuli [250 trolands (td) and 10 td] were equated on the basis of individual heterochromatic flicker photometry functions. Measured Pc discrimination sensitivity was lower in the older group than in the younger group at both light levels, and the performance difference between the age groups was approximately constant across the spectrum. The difference between discrimination at 10 and 250 td was relatively small for the younger group but larger for the older group, indicating a selective performance decrement for older observers at low light levels. The data were modeled as a sum of differential responses from S-cone and L/M-cone chromatic channels. The model and the data indicate similar age-related losses of sensitivity in the two channels, perhaps secondary to receptorial sensitivity losses.

Adult↗

PubMed1999

Aging and the saturation of colors. 2. Scaling of color appearance.

Saturation of two sets of stimuli was scaled by 21 color-normal observers (ten younger and 11 older observers, mean ages: 30 and 73 years). Circular fields, 1.2 degrees in diameter, were presented in Maxwellian view as 1.5-s flashes with 3-s interstimulus intervals. Stimuli were mixtures of broadband light [CIE(x, y) = (0.35, 0.39), 200 trolands (td)] and monochromatic light (420-700 nm, 50 td). Monochromatic lights were equated by the 1978 2 degrees fundamental observer's luminosity function in one set of stimuli [J. J. Vos, Color Res. Appl. 3, 125 (1978) and by each observer's heterochromatic flicker photometry function in the other set of stimuli. Comparing the two age groups reveals no sizable differences in saturation for either set of stimuli, neither supporting nor refuting neural compensation for age-related increases in ocular media density (OMD). Examining short-wavelength saturation as a continuous function of estimated OMD reveals a more complicated pattern of results, however, suggesting substantial compensation over a certain range of OMD values but incomplete compensation for observers with the highest OMD values.

Adult↗

PubMed1998

Effects of known variations in photopigments on L/M cone ratios estimated from luminous efficiency functions.

The extent to which known variations in photopigment lambda max and optical density may affect cone ratios estimated from the spectral luminous efficiency function (LEF) was examined. LEFs were generated using L- and M-cone fundamentals, one of which had been shifted in lambda max (+/- 1, 2, 4 or 6 nm) or varied in peak optical density (increased or decreased by 10, 25 or 50%). A curve-fitting program was then used to estimate the L/M cone ratios for the generated LEFs assuming standard L- and M-cone fundamentals. These modeling exercises indicate that L/M cone ratios estimated from LEFs are highly correlated with long-wave sensitivity and with known variations in L-cone lambda max. Variations in M-cone lambda max and photopigment optical density for both cone types are also correlated with L/M cone ratios, but have much less impact on the estimated ratios.

Algorithms↗

PubMed1998

M- and L-cones in early infancy: I. VEP responses to receptor-isolating stimuli at 4- and 8-weeks of age.

A silent-substitution technique combined with measures of the visually-evoked potential (VEP) was used to determine whether M- and L-cones are functional in early infancy. Data were successfully collected from twenty six infants in response to three receptor-isolation conditions (rod, M- and L-cone isolation) and a luminance-modulation condition. The efficacy of the receptor-isolation conditions was first verified by measuring VEP responses from both dichromatic and color-normal adults to each of the receptor-isolation conditions. Both 4- and 8-week-old infants demonstrated VEP responses to the M- and L-cone isolating stimuli, though the amplitude of the the responses at 4-weeks were reduced compared to those at 8-weeks. These data suggest that the functioning of M- and L-cones can be differentiated as early as 4-weeks of age.

Adult↗

PubMed1998

M- and L-cones in early infancy: II. Action spectra at 8 weeks of age.

Field sensitivities were measured under conditions of M- and L-cone isolation for seven infants (8-12 weeks-old) and two adults, using silent-substitution and the visually evoked potential (VEP). The efficacy of the receptor-isolation conditions were first verified by measuring psychophysical and VEP-derived action spectra from two color-normal adults under conditions of M- and L-cone isolation. M- and L-cone action spectra obtained from the two methods were found to be similar to the Smith and Pokorny M- and L-cone fundamentals, respectively. The VEP-derived action spectra obtained from infants and adults were well fit by the Smith and Pokorny M- and L-cone fundamentals. These data, in conjunction with our previous study, confirm that M- and L-cones are operating by 8 weeks and possibly as early as 4 weeks of age.

Adult↗

PubMed1998

M- and L-cones in early infancy: III. Comparison of genotypic and phenotypic markers of color vision in infants and adults.

Genetic analyses were performed on five male children (approximately 3 years), two suspect color-normals and three suspects for congenital color vision deficiencies. These classifications were based on visually-evoked potential (VEP) responses to M- and L-cone-isolating stimuli obtained in a previous study when each subject was either 4- or 8-weeks old. The present analyses were performed in a blind study to characterize the genotypes of these subjects. Four male adults with various color vision phenotypes were also tested as a control. DNA was isolated using a non-invasive technique followed by polymerase chain reaction (PCR) amplification and restriction enzyme analysis to examine the genomic DNA of each subject. The genetic analyses confirmed the VEP identification of two color defective infants, and were consistent with the diagnosis of two other infants as color normal. A third infant was predicted by VEP analysis to have a protan defect, but he did not have a gene array typically found in protan observers.

Child, Preschool↗

PubMed1998

The area of complete scotopic spatial summation enlarges with age.

The maximal area of complete scotopic spatial summation (Ricco's area) was determined for 50 subjects ranging in age from 19 to 87 yr. Increment thresholds were measured for 10-ms, 520-nm circular test lights of varying diameters that were superimposed and concentric with a 10 degrees, 640-nm circular background. The test lights were imaged in Maxwellian view along the horizontal meridian, 6 degrees nasal from a foveal fixation point. The results demonstrate a statistically significant enlargement of Ricco's area with age. The average angular subtenses of Ricco's areas for the ten youngest (mean = 26 yr) and ten oldest (mean = 75 yr) observers were approximately 48 and 69 arc min, respectively. Model simulations based on a series of optical transfer functions of the eye and varying degrees of intraocular light scatter for younger and older observers show that preneural factors cannot account for these results. Therefore changes in neural mechanisms must be invoked to explain the enlargement in the size of Ricco's area under scotopic conditions.

Adult↗

PubMed1997

Sensitizing properties of spectral lights in 4-month-old human infants.

Previous studies of infant attention, learning, and memory have revealed that certain stimulus properties may increase an infant's arousal or excitation level, thereby increasing responsiveness and facilitating the encoding and processing of information. In a series of experiments aimed at identifying stimulus determinants of sensitization, we examined visual responses from 4-month-old infants to spectral lights. Habituation data were obtained from 92 full-term infants separated into one of five groups. Each group viewed either a broadband white light (correlated color temperature approximately 2800 K) or one of four different spectral lights (lambda d = 470, 510, 570, or 650 nm) approximately corresponding to the elemental hues blue, green, yellow and red, respectively, for adults with normal trichromatic vision. Stimuli were equated in luminous efficiency for a standard infant observer. Stimulus fixation was recorded for twelve 10-s presentations, each separated by 10-s interstimulus intervals (ISIs). The results show that mean fixation times to the red and green lights were significantly greater than those for the blue and white light. Mean fixation time for the yellow light was also reduced (significantly) compared to the red but not the green light. These results suggest that the chromatic properties of red and green spectral lights may be more sensitizing to infants than those of the blue, yellow, or white lights.

Adult↗